Grazing animal nutrition.pdf

7/27/2019 Grazing animal nutrition.pdf

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UNIVERSITY OF SASKATCHEWAN

DEPARTMENT OF ANIMAL & POULTRY SCIENCE

ANIMAL SCIENCE 410.3

GRAZING ANIMAL PRODUCTION

LECTURE MANUAL 1998

by

Dr. Roger D.H. Cohen


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BEEF CATTLE HERD MANAGEMENT

INTRODUCTION

Cattle have been valued as a source of food, clothing and power for as long as people havedomesticated animals. In today's societies, beef consumption is still a major indicator of the standardof living in a population.

The beef cattle of the world belong to two species: Bos taurus andBos indicus. Bos taurus cattleare largely European in origin and are adapted to temperate climates. Some breed representativesinclude Hereford, Angus, Shorthorn, Simmental, Charolais, Maine-Anjou and Limousin. Bosindicus cattle are Afro-Asian in origin and are adapted to tropical climates. The most importantbreed representatives are Brahman, Red Sindhi and Sahiwal.

Beef cattle were first introduced to North America from Spain by Christopher Columbus on hissecond voyage in 1493. Although British and European breeds of cattle were introduced to NorthAmerica in the early 17th century, there was little interest in selection and improvement of cattle

until the late 18th century. Cattle were initially required to graze the existing native rangelands withno provisions for supplementary feeding during winter, drought and other extreme climaticconditions. There was little or no correction of nutritional deficiencies in the forage. This methodof husbandry still exists today in many parts of the world.

The economic value of cattle in developed societies has increased greatly during the 20th century.For example, in Canada by 1988, beef production accounted for 55.2% of the farm receipts fromlivestock and 26.9% of the total farm receipts from all agricultural enterprises. Nevertheless, thebeef industry is still the least intensive of all agricultural industries.

Because of low fecundity and the great length of time taken for progeny to reach slaughter weight,the beef cow produces only about 70% of her body weight as slaughter weight per year. Thiscompares unfavorably with the sow who produces about 8 times her body weight and the hen who

produces about 100 times her body weight as slaughter weight per year. However, cattle consumeonly 17% of their feed as concentrates compared with 85% for swine and 94% for poultry and are,therefore, much less competitive with man for feed resources. Cattle derive their agriculturalimportance from the effective conversion of energy not useable by people (eg. grass and cropaftermath) into high quality protein and other essential nutrients for human consumption.

STRUCTURE OF THE BEEF INDUSTRY

The beef industry is divided into two enterprises, cow/calf and feeder. These may be conductedindependently, with transfer of ownership of calves at weaning to independent premises;simultaneously, with retention of calves on the original farm through to slaughter; or as an

integrated enterprise, with retention of ownership of the cattle, but transfer of them to someindependent premises at some time between weaning and slaughter.

THE COW / CALF ENTERPRISEThe cow/calf enterprise can be sub-divided into the production of purebred and commercial cattle.Purebred cattle are sources of germ plasm, most commonly bulls though occasionally heifers, forother purebred and commercial breeders. Purebred cattle are eligible for entry in a breedassociation registry and represent a product descended from a selected long line of ancestors ofsimilar type and breed. They are produced with the aim of improving efficiency of production,


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frame size and carcass quality. Calves which are not kept in the herd for replacement purposes arenot usually fed to slaughter but are fed to at least one, and frequently two years of age and sold asbreeding stock. The costs associated with feeding are usually greater than those of commercialcattle. Promotion and advertising of the product through the media or show ring is also an integraland expensive part of the purebred enterprise. Although showing beef cattle has declined inimportance in the purebred enterprise, it remains a popular way of advertising in the industry.

Performance testing of cattle has increased in popularity in the last 20-30 years because of itsability to provide proof of superiority. However, there is evidence that performance testing mayhave been used more as a marketing tool than as a means of improving productivity in the purebredindustry.

In the commercial cow/calf enterprise, calves are produced to be sold at weaning, carried throughto slaughter or to be reared as replacement heifers. Crossbred cows are frequently the basis of thecommercial herd and these cows are usually bred to bulls of a third breed (terminal sire). Forexample, popular crossbred cows are Hereford x Angus or Hereford x Simmental and Charolaisbulls are popular terminal sires but combinations of all breeds are in use in the industry.

Most beef calves are born in late winter or early spring to keep winter feeding costs at a minimumand to allow the cow to make maximum use of fresh spring/summer pasture growth for lactation.

Nevertheless, fall calving is practiced in some herds to reduce the incidence of neonatal calfdiarrhea or to take advantage of higher prices for calves sold in spring or to increase pastureutilization by the calf. However, both growth rate and weaning weight are usually reduced in fall-born compared with spring-born calves. Milk yield is also lower in fall compared to spring calvingcows, the advantage increasing in favor of spring calving cows if ambient temperatures during

winter fall to -5oC or below. In addition, fall-calving cows must be bred during winter but bullfertility is lower during winter than summer and bull libido is highest in spring. Furthermore,there is an increased requirement for feed in the winter if the calves are born in the fall because thenutritional requirements of the lactating cow are greater in winter than spring and summer. Theprovision of additional feed for fall-born calves is also important to ensure adequate nutritionthrough winter. All these requirements increase feed costs relative to spring-born calves.Many cow/calf operators sell their calves at weaning to operators in the feeder enterprise but

retention of ownership through to slaughter is becoming increasingly more common. Ownershipmay be retained by either feeding the calves from weaning to slaughter on the home farm or ranch,or moving the calves at some stage between weaning and slaughter to the premises of a feederenterprise operator. The latter is usually referred to as 'custom feeding'.

Plant breeders have been effective in providing varieties of crops that are more adapted to lowerrainfall, local temperatures and day-length, fewer frost-free days, and that are more resistant topests and diseases. This has resulted in a continual encroachment of profit motivated cashcropping into the traditional rangeland areas grazed by the cow/calf herd. The result has been adeclining number of farms and ranches, which depend on beef production as their major source ofincome. For example, in Canada there are approximately 80,000 cow/calf herds and the averagesize is less than 50 cows/herd. Fewer than 15% of Canadian herds derive their major source ofincome from beef cattle. In the United States, approximately 74% of farms and ranches have

fewer than 50 cows.

SASKATCHEWAN BEEF INDUSTRY PERSPECTIVE

In 1975 there were 1.3 million beef cows in Saskatchewan. By 1986 the number of cows had declinedto 761,000. This decline reflected high grain prices, high interest rates and government policy which


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favored grain production over livestock production. By 1994, the number had risen again to 1.2million reflecting lower grain prices, lower interest rates and changes in the grain transportation act.This is typical of the cattle cycle, which is accentuated more in Saskatchewan than the other provincesbecause of the importance of the grain industries. Atypically, cattle numbers have remained fairlyconstant since 1994, reflecting generally good seasonal conditions and continued low grain prices. Theaverage cow herd size in Saskatchewan is 55.

The majority of cattle in Saskatchewan are complementary to cash cropping. Frequently, the farm hassome land unsuitable for cropping but suitable for pasture and hay (i.e. saline, rocky, treed or light soilareas). Cattle are also a means of using crop aftermath (stubble, straw, chaff, etc.) or they fit somecrop/pasture rotation. Very few beef cows are kept in confinement (corrals, barns, etc.) year round,though most cows are held in confinement or semi-confinement (i.e. small paddocks near the home) forthe winter months to facilitate feeding and management, particularly at calving.

The profitability of a cow/calf operation depends primarily on:

1) High percentage of calf crop at weaning and heavy weaning weights of calves.2) Maximum utilization of pasture and cheap roughage.3) Low capital investment/cow in land, buildings and equipment.

4) A high pregnancy rate in the replacement heifers5) Low labor requirements.6) Low expenditure on supplementary feeds.7) Effective management.

ANNUAL CYCLE OF A COW-CALF OPERATION:

The average gestation length of a beef cow is 283 days and post-partum anestrus is about 40 days.This allows just 42 days for the cow to conceive if she is going to produce a calf within a 365 dayperiod (i.e. one calf /year). The annual cycle of a beef cow is shown in Figure 1. A high level ofreproductive performance is essential to an efficient cow/calf operation. The percentage calf crop isa measure of fertility, mothering ability and calf survival and has a direct bearing on production

costs and profitability. Although disease and genetics will influence reproductive performance, thegreatest benefits will be achieved from careful consideration of herd nutrition. The cow mustremain as a productive unit in the herd for as long as possible. This means she must breed at 12-15 months of age and produce her first calf by the time she is 2 years old. The heifer onlybecomes an economically productive unit when her first calf is sold. The nutritional managementof the replacement heifer herd has a major influence on her reproductive performance.

The beef cow reaches her maximum productive potential when she is 4-5 years old and shouldmaintain that level until at least 10 years of age. Failure to conceive at any time before 10 years ofage represents a major loss of productive potential. Heavy weaning weights of calves are directlyassociated with the nutrition of the calf and nursing cow. However, calf weaning-weight is alsoinfluenced by age at puberty in the dam and by the length of the post-partum anestrus period. For

example, calves which are conceived in the first and second estrus cycles of the breeding season(that is within the first 21 and 42 days respectively of exposure of heifers to bulls) growsignificantly faster from birth to weaning and weigh more at weaning than calves which areconceived later in the season. Furthermore, heifers that calve early at the first calving have higheraverage annual lifetime calf production than heifers that calve late at the first calving.


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Figure 1. The annual cycle of a cow/calf operation.

FEEDING THE BEEF COW

There are 3 phases of primary importance:

1) Weaning to calving (fall & winter)2) Calving to re-breeding (spring & early summer)3) Breeding to weaning (summer & early fall)

1. Weaning to calving

When calves are weaned in the fall, all cows should be pregnancy tested and only pregnant cowsshould be fed during the winter period. Generally, it is not economical to feed older cows for slaughterso these cows should be shipped immediately following pregnancy testing. However, in some cases,cows in poor condition will gain weight very and it may be economical to feed these cows good qualityroughage and grain for a short period (60-90 days) to take advantage of this rapid weight gain and highfeed conversion efficiency. Most often, it will be economical to feed young cows and heifers (i.e.cows less than 3 years.) for 30-90 days if they are open but in good condition as it may still be possibleto receive Canada A grades for these carcasses.

After weaning, the female herd should be split into 5 groups because different groups of animals in theherd will have different requirements. These groups are:

1) Mature cows in good condition - fed low to medium quality forage to maintain weight or, if fed high

Cow Cycle

Pregnant &

dry160 days

Post-partum

40 daysBreeding

42 days

Pregnant &

lactating

123 days


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quality forage, intake should be limited to maintain weight until about 6 weeks before calving.2) Mature cows in poor condition should be fed medium quality forage to gain 0.1 - 0.5 kg/dayotherwise these cows will be in poor condition for calving and likely not conceive the followingbreeding season.

3) Two-year-old cows (i.e., those that have just weaned their first calf) should be fed medium to high

quality forage as these cows are still growing themselves and have undergone the severe stress of a firstlactation. These cows should be fed to gain 0.3 - 0.6 kg/day.

4) Bred replacement heifers - these are still growing and should reach a frame size that will allow easycalving but should not be over-fat as this will cause dystocia. They require a medium to good qualityforage perhaps with some gain and should grow at about 0.5 kg/day.

5) Replacement heifer calves. These should be fed high quality forage and some grain (e.g. 8 kgbrome-alfalfa hay + 3 kg oats or 2 kg barley/day) to gain 0.6 - 0.8 kg/day in order to reach a targetbreeding weight of 320-350 kg at 14-15 months of age by spring.

Groups 3 and 4 or 2,3 and 4 can be fed as a single group if cattle numbers or facilities do not warrant 5groups. Cows should be on a rising plane of nutrition 3-4 weeks before calving and on high quality

forage after calving. This will mean increasing the quality of forage and/or providing some additionalgrain.

The condition of cows going into winter has a major effect on the amount and quality of feed that theywill need. Cows in thin condition in the fall must gain weight throughout winter or they may haveproblems calving and may have weak or moribund calves. The cow may produce little milk and sowean a light calf and she may not conceive when re-bred in spring. Cows in good condition in fall needonly enough feed to maintain their weight until calving.

The wintering period can be divided into the second and third trimesters of pregnancy.

Second Trimester

During the second trimester, nutrient requirements are the lowest for the whole reproductive cycle ofthe cow. Thus, depending upon their condition, they can be fed low quality forage or up to 75% strawand 25% grain and protein supplement, or other combinations of straw and good quality forage. If amedium-good quality forage is fed it may be necessary to limit feed to achieve the desired weightchange as defined earlier. It is during this period that the poorest quality stored feed should be fed.

Third Trimester

If cows are being fed to achieve their prescribed rate of gain for the second trimester it should not benecessary to alter the feeding program until 4-8 weeks before calving. However, if they are notachieving expected weight gains during the second trimester it may be necessary to increase the quality

or quantity of feed given during the first half of the third trimester because the nutrient requirements areincreased to meet the needs of the fetus, which is growing rapidly during the 6-9 month gestationperiod. It is during this period that cold weather will increase the energy requirement of the beef herd.

During the last 4-8 weeks of gestation, the amount of nutrients supplied should be increased by about15% either by increasing the amount or quality of the ration or both.

2. Calving to re-breeding

This is a particularly important time for the cow. Her requirements are high due to lactation and she


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must be on a high plane of nutrition to ensure:a) Adequate milk for the calfb) Quick return to estrusc) Good conception rate

Inadequate nutrition at this time will result in:

a) a greater number of days between calving and estrusb) a longer calving period next yearc) less likelihood of breeding every yeard) large differences in age between oldest and youngest calvese) large differences in weaning weight between oldest and youngest calvesf) less even calf crop and reduced incomeg) lighter replacement heifers resulting in reduced heifer conception rates.

The cow will be on pasture range for much of this period.

3. Breeding to Weaning

Cow nutrient requirements will begin to decline following breeding as she will have reached her lactationpeak and the calf will be getting increasingly more nutrients from dry feed (eg. pasture) and less frommilk. The decline in cow nutrient requirements is gradual to weaning. The cow will usually be on rangeor pasture for all of this period.

Feed Intake

Beef cattle will consume feed on a dry matter basis at the rate of 1-3% of their body weight. Feedconsumption will vary depending on the type of ration, the age and condition of the animal and the stageof its production cycle (i.e. eating to meet energy demands eg. for lactation). However 3% is the upperlimit, in most cases cattle have difficulty eating more than 2.5% of body weight.

Table 1. Approximate Consumption Estimates of Some Feeds on a 90% DM basis for a 550kg beef cow.

__________________________________________________________________

Feedstuff Approximate Maximum ConsumptionDMD % kg/d % of BW

___________________________________________________________________

Excellent quality hay 65 16.5 3Very good quality hay 60 13.75 2.5Medium Quality hay 55 11.0 2Poor hay, Barley straw 45 7.5 1.5Wheat straw 35 - 40 5.5 1Silage 60 - 65 13.75-16.5 2.5 - 3

__________________________________________________________________


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Minerals and Vitamins

Most winter feeding programs for cows require supplemented minerals. Cobalt iodized (blue) salt ortrace mineralized salt should be available on a free-choice basis. Rations based on hay should have 1:1Ca:P supplement available while rations based on cereal silage or straw and grain should have 2:1 Ca:Psupplement available. Other minerals to consider which are frequently deficient in prairie feeds are Cu,

Zn, Mn and Se. Cows should consume 20-30 gm/head/day and it may be necessary to feed mineralswith salt to ensure adequate intake. It is not usually economically feasible to process forage for cowsso minerals are best fed free choice rather than mixed with the feed or they can be fed in a grainsupplement.

A beef cow requires 40,000 IU of Vitamin A/day before calving and 70,000 IU Vitamin A/day aftecalving until she has access to green grass. Vitamin A is stored in the liver so it can be injected every 1-2months or fed daily.

Table 2. Mineral Requirements and Maximum Tolerable Levels for Beef Cattle_____________________________________________________________________

Maximum

Suggested TolerableMineral Value Rangea Levelb

_____________________________________________________________________

Calcium, % - See below 2Cobalt, ppm 0.10 0.07 to 0.11 5Copper, ppm 8 4 to 10 115Iodine, ppm 0.5 0.20 to 2.0 50Iron, ppm 50 50 to 100 1000Magnesium, % 0.10 0.05 to 0.25 0.40Manganese, ppm 40 20 to 50 1000Molybdenum, ppm - - 6

Phosphorus, % - See below 1Potassium, % 0.65 0.5 to 0.7 3Selenium, ppm 0.20 0.05 to 0.30 2

Sodium, % 0.08 0.06 to 0.10 10c

Chlorine, % - - -Sulfur, % 0.10 0.08 to 0.15 0.40Zinc, ppm 30 20 to 40 500____________________________________________________________________

aThe listing of a range in which requirements are likely to be met recognizes that requirements for most minerals are affected

by a variety of dietary and animal (body weight, sex, rate of gain) factors. Thus, it may be better to evaluate rations based on

a range of mineral requirements and for content of interfering substances than to meet a specific dietary value. For most

places in Saskatchewan, where cattle are watered from deep wells during the winter and the water has a high sulphate content

(>500 ppm), the requirements for Cu, Zn and Mn can be increased to 25, 70 and 90 ppm respectively.

bFrom NRC (1980).

c10% sodium chloride.

P req. = 8-30 g/d depending on weight, age, sex, physiological condition, etc. OR 0.2 - 0.4%.

Ca req. = 10-45 g/d depending on above factors OR 0.2-0.6%.


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Table 3. Maximum Tolerance Levels of Certain Toxic Elementsa

_____________________________________________________________________

Element Maximum Tolerable Level, ppm_____________________________________________________________________Aluminum 1,000

Arsenic 50 (100 for organic forms)Bromine 200Cadmium 00.5Fluorine 20 to 100Lead 30Mercury 2Strontium 2,000_____________________________________________________________________aNRC (1980). Table 4, Mineral Requirements and Maximum Tolerable Levels for Beef Cattle.

Energy and Protein Nutrition of the Beef Cow

The energy and protein requirements of a beef cow increase as she moves through the second and thirdtrimesters of her pregnancy and they increase further during lactation (Table 4; Figure 1). Daily dry matteintake also increases through these times (Table 4) however this increased intake alone may not besufficient to meet requirements without an accompanying increase in feed quality. Table 5 presentapproximate energy and protein values of some feedstuffs commonly fed to beef cows and Table 4indicates the ability of three of these feeds (medium quality brome/alfalfa hay; barley straw; barley silageto meet these requirements for a 550 kg cow at thermoneutrality.

Table 4. Nutrient Requirements of a 550 kg cow at Thermoneutral Conditions_____________________________________________________________________

Production Daily Daily Requirements % in Diet DMICycle Gain ME TDN CP ME TDN CP(Mcals) (kg) (g) (Mcal/kg) (%) (%) (kg/d)

_____________________________________________________________________

2nd trimr 0 16.7 4.6 657 1.76 48.6 6.9 9.5

3rd trimr 0.4 19.5 5.4 790 1.91 52.8 7.8 10.2

Lactating1st 3-4 months5 kg milk/d 0 21.5 5.9 1001 2.03 56.1 9.5 10.610 kg milk/d 0 25.8 7.1 1299 2.38 65.8 12.0 10.9

_____________________________________________________________________


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Figure 2. Theoretical energy requirements of a mature 550 kg (1200 lb) beef cow.

Table 5. Energy and Protein Contents of Some Feeds (Hay Equiv. Basis)_____________________________________________________________________

Feed DMD ME TDN CP(%) (Mcals/kg) (%) (%)

_____________________________________________________________________

Excellent alfalfa hay 65 2.20 59 18.3Good alfalfa hay 60 2.18 57 15.9Med. Brome alfalfa hay 55 1.76 54 10.9Barley straw 45 1.45 40 3.9Barley silage 65 2.30 60 10.8Barley 90 3.30 75 12.0_____________________________________________________________________


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Table 6. Ability of Some Forages to Meet the Requirements of a 550 kg Cow at Thermoneutrality(Hay Equiv. Basis)

____________________________________________________________________

Estimated 2nd Trimester 3rd Trimester LactatingIntake Intake (kg/d) Intake(kg/d) (5 kg/d)

Forage (kg/d) to meet reqt. To meet reqt. Intake to meetfor for reqt. forEnergy Prot. Energy Prot. Energy Prot.

_____________________________________________________________________

Med. Brome/Alfalfa Hay 11 9.5 6 11 7.3 12.3 9.2

Barley Straw 8 11.5 16.8 13.4 20.3 14.8 25.7

Barley Silage 14 7.3 6.1 8.5 7.3 9.3 9.3_____________________________________________________________________

It can be seen from Table 6 that barley silage will probably provide sufficient energy and proteinthroughout the cycle for a cow producing 5 kg milk/day but additional energy (grain) would be requiredfor higher milk production. Brome/alfalfa hay would supply sufficient protein but insufficient energy for alactating cow producing 5 kg milk/day whereas barley straw would not provide sufficient energy oprotein for a 550 kg cow at any stage of its production cycle.

Tables 5 and 6 apply to temperatures within the thermoneutral zone (Figure 3). Although temperaturebelow the lower critical temperature (cold stress) may stimulate intake (Figure 4), they will also increasethe requirements for dietary energy required for the maintenance of normal body temperature. Thesincreased requirements may not always be able to be met by increased feed intake (Table 6).

Lower UpperCritical Critical

Temperature Temperature

Thermoneutral Zone

Optimum for performanceand growth

Cool Warm

Low HighEFFECTIVE AMBIENT TEMPERATURE

Figure 3. Relationship of temperature to thermal zones.


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-20 0 20 40

Figure 4. Effect of environmental temperature on feed intake in cattle.

Effect of Environment on Energy Nutrition

1) Effect of cold on digestibilityResting metabolic rate is a measure of the maintenance energy expenditure of animals. As the temperaturfalls below thermoneutrality (~20oC) resting metabolic rate increases in order to maintain normal bodytemperature (Figure 5). In addition, there is a depression in the digestibility of feed as temperature fall

below thermoneutrality (Figure 6). As a general rule there is a 1.8% depression in DMD/10oC below

20oC. This reduces the effective metabolizable energy content of the feed (Table 7).


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Figure 5. The effect of temperature on energy expenditure of beef cows.

Figure 6. Effect of physical form and temperature on the digestibility of two forages. (Long and pelletedbrome grass represented by open and filled triangles and chopped and pelleted timothy by openand filled circles respectively).

Table 7. Effect of temperature on feed ME content (Mcal/kg)___________________________________________________________________

Temperature Digestibility (% DM) at 20oC50 55 60_____________________________________________________________________

20oC 1.65 1.83 2.01

0oC 1.59 1.76 1.94

-30oC 1.50 1.67 1.83_____________________________________________________________________


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Using the information from figures 4, 5 and 6 and table 7, the ability of high and low energy rations tomeet the requirements of a beef cow during winter is illustrated in Figure 7.

Figure 7. The relationship between intake energy (IE), energy requirement (ER) and temperature in beecattle.

The feed intake requirements of a 550 kg cow in the third trimester of pregnancy (kg DM/d) are shown inTable 8 for feeds of 50, 55 and 60% DM digestibility at different temperatures.

Table 8. Feed requirements for a 550 kg cow in the 3rd trimester of pregnancy.____________________________________________________________________

Temperature Digestibility (% DM) at 20oC50 55 60

____________________________________________________________________

20oC 11.8 10.7 9.70oC 12.3 11.1 10.1

-30oC 13.0 11.7 10.7% increase from

20oC to -30oC 10.2 9.3 10.3_____________________________________________________________________

2) Wind and coat type and weight of cow

Cold stress is dependent on many factors. For example,Cold stress = f (temperature, wind, solar radiation, precipitation, coat type, cow weight .....)

There are tables indicating wind chill factors for cattle and Table 9 is an extract from such tables.


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Table 9. Wind Chill Factors for Cattle with Winter Coats____________________________________________________________________

Wind Speed Temperature (oC)(km/hr) -1 -12 -23____________________________________________________________________

Calm - 1 -12 -2316 - 7.7 -18.3 -29.432 -12.8 -23.3 -34.464 -38.9 -50 -61.1____________________________________________________________________

Thus if ambient temperature is -23oC and a wind is blowing at 32 km/hr, a cow experiences an effective

temperature of -34.4oC.

This emphasizes the importance of wind breaks since if the wind speed can be reduced to 16 km/hr she

experiences a reduction of 6 degrees to -29.4oC.

The term "Degrees of Coldness" is always positive and equivalent to a wind adjusted temperatureMaintenance energy costs are increased depending on the degree of coldness, coat type and weight orcondition of cow (Table 10).

Table 10. Percentage increase in ME costs/oC of coldness for cows in poor condition (360 kg)or good condition (550 kg) with different coat types.

_____________________________________________________________________

Coat Type Cow weight (kg)360 550

_____________________________________________________________________

Heavy winter coat 1.25 1.1Light winter coat 2.0 1.8Wet winter coat 3.6 3.4_____________________________________________________________________

Thus, assuming a cow weighs 550 kg in the third trimester with a thermoneutral ME requirement of 19.5Mcals, the ME requirements can now be re-calculated. If the cow has a heavy winter coat (requiring an

increase of 1.1%/oC of coldness) and the temperature is -23oC with a 16 km/hr wind and no shelte

(29.4oC of coldness or -29.4oC temperature equivalent). The re-calculation is as follows:

At 20oC ME Requirement = 19.5 Mcal

at 29.4oC of coldness = 19.5 + [(29.4 x 1.1 x 19.5)/100]= 19.5 + 6.3= 25.8 Mcals

Similarly, if it is calm but other factors remain unchanged

ME Requirement = 19.5 + 4.9= 24.4 Mcals


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Therefore: A cow eating hay at 45% DMD containing 1.45 Mcals/kg ME at -30oC (Table 5) would requir25.8/1.45 kg DM = 17.8 kg DM at 16 km/hr windand 24.4/1.45 = 16.8 kg DM if calm

compared with 13.4 kg DM at thermoneutrality (20oC).

Alternatively, a 60% DMD hay containing 2.18 Mcals/kg ME would require 11.8 kg DM at -23oC and a16 km/hr wind OR 11.2 kg DM if calm.

A third trimester cow will not be able to eat more than about 2 - 2.5% of its body weight so for a 550kg cow maximum feed intake is about 11 - 13.75 kg DM.

Thus under these extreme cold conditions it would be necessary to feed high quality hay of about 55 - 60%DMD or some grain.

Table 11 provides an example of the benefits that can be obtained from adjusting feed levels for cowsduring winter. The data come from Nebraska where the winters are a bit milder than on the CanadianPrairies but there are no data of this sort from Canada.

Table 11. Effect of Adjusting Feed Levels for Cows during Cold_____________________________________________________________________

Ration adjusted Ration not adjustedfor coldness for coldness

_____________________________________________________________________

Wt. change last 135 days ofgestation (kg) 52 12Wt. change at weaning (kg) -48 -54Net Wt. change (kg) 4 -42

Daily milk prod. (kg) 9.2 7.9% cycling in 60 days frommean calving date 82 65

_____________________________________________________________________

Heifers and Calves

The principles used for feeding the cow herd can be applied in the same way for feeding the other majorgroups in the breeding herd i.e. bred heifers, replacement heifers and bulls. Over-feeding bulls can beworse than underfeeding as it may reduce libido and semen quality and hence calf crop. Rule of thumbindicates that: mature bulls require about 50% more feed than a mature dry cow and growing bulls (2 year

old) require slightly more than that.


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HOUSING

Beef cows do not require elaborate housing. Protection from the wind is the most important requirement(Figure 8). Cows should be bedded on straw on high, wind-protected mounds or in a shed with the openside facing south. Shelter can be provided by groves of trees or slatted fences 2.5 m high and 20%porosity (i.e. 20cm boards vertically placed with 5cm spaces between them). A porous fence is more

effective than a solid fence as the latter creates a vacuum, which increases turbulence and allows snowbuild up.

Figure 8. Example of shed and porosity fencing for wintering beef cows.

CALVING

A high level of reproductive performance, or fertility is essential to an efficient cow/calf operation.Percent calf crop is a measure of fertility, mothering ability and calf survival. Percent calf crop weanedand the weaning weight of the calves both have direct effects on production costs and returns (Tables 12and 13). These tables assume:

a) Cow costs = $365/yearb) Herd size = 100 cows

c) Calf weaning weight = 215 kgd) Calf price = $2.20/kg ($1.00/lb)NOTE: These assumptions are not necessarily correct as costs etc. will vary from farm to farm andrepresent only a simplified example.

Table 12. Economic implications of calving % on cost._____________________________________________________________________

Calf crop (%) Total kg of Gross Cost Net Incomecalf weaned Income per calf weaned

______________________________________________________________________($) ($) ($)

100 21,500 47,300 365 10890 19,350 42,570 406 6780 17,200 37,840 456 1770 15,050 33,110 521 -4860 12,900 28,380 608 -135

_______________________________________________________________________


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Table 13. Effect of % calf crop on average weight (kg) of calf weaned and gross economic return / cowbred.

Calf Crop(%)

Heavy Medium Light

100 250 204 182

90 225 184 16380 200 163 14570 175 143 127

Difference / cow bredBetween 100 and 70%@ $2.65/kg

198.75 161.65 145.75

Gross return / cow bredfor heavy, medium andlight calves @ 90%weaning and $2.65/kg

596.25 487.60 431.95

The most critical times when % calf crop is reduced are:

1) peri-partum (around calving)2) at breeding.

FACTORS AFFECTING LOSSES AT CALVING

1. Dystocia :

Dystocia is a greater problem in heifers than cows and can be caused by the following:

a) Calf is too large and/or cow is too small. Causes may be:

(i) Poor breeding management. For example use of a large framed bull on a small framed cow (i.e.Simmental x Angus) or use of a large framed bull on heifers (i.e. Simmental x heifers of any breed).Small framed cows should be bred to small-medium framed bulls (i.e. British Breeds) and heifersshould always be bred to small-medium framed bulls (i.e. Angus, Hereford, Shorthorn). The bullshould also have had a low weight at birth.(ii) Poor nutritional management. For example, cows which are overfed during pregnancy often havedifficulty calving because they become over-fat, muscular contractions are weak and ineffective sincefetal growth rate has been too high and the fetus has become too big and hence difficult to expel.

Proper management can reduce the incidence of dystocia and calf loss due to the above factors. The

overriding factor causing dystocia is too great a birth weight of the calf. The effect of the pelvic area ofthe dam is overemphasized.

b) Mal-presentation of the fetus. Pre-partum management will have little effect on this cause of dystociaalthough, over-fatness of cows may contribute to this problem because there may be an increasedincidence of calves failing to turn in- utero for a normal presentation. However, proper calvingmanagement can greatly reduce losses to mal-presentations. An understanding of the birth process isessential.


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There are three stages to parturition: (1) the preparatory stage (2) expulsion of the fetus and (3)expulsion of the placenta (afterbirth).

Heifers usually take longer to calve than cows. On the average, a cow will spend 2 to 4 hours preparingfor calving but heifers may spend up to 8 or 10 hours. However, once calving has begun, it generallydoes not take more than an hour for the calf to be expelled. Prior to birth, the uterus begins contracting,

the cow becomes restless and the fetus is slowly pushed against the cervix causing it to dilate evenfurther. Contractions occur about every 15 minutes and last from 15 to 30 seconds. During the laterstages of birth the contractions become more frequent, about every 3 minutes, and much stronger. Atthis time voluntary muscle contractions of the stomach also occur. The calf is expelled into the birthcanal.

The normal delivery position is head and front feet forward. However, as shown in the followingillustrations there are a number of abnormal presentations, which may have to be confronted. The bestadvice is, if a cow has not calved 2-3 hours after preparation has begun, call a veterinarian. Where this isnot practical because of distance or time, the only solution is to reposition the calf for either a front orrear delivery.

Following birth, uterine contractions continue and the placenta, or afterbirth, is expelled. This usually

happens within 12 hours. If the placenta is not expelled within this time it is referred to as retainedafterbirth and may require that the cow be cleaned. There is no real rule of thumb as to when a cowshould be cleaned. If the cow is active, alert and eating well she can be left to clean herself, even if ittakes two or three days. On the other hand, a cow that is listless and has a poor appetite should receivethe immediate attention of a veterinarian or, at the least proper antibiotic medication. The forced removalof the placenta can cause internal tears, which, in turn, can cause sterility. It is preferable to let the cowclean by herself if there is no threat of abnormal secondary infection.

Assistance should be given before a cow or heifer has been in the preparatory stage for 4-6 hours. After6 hours the calf is probably dead. Assistance can be given using calf chains or a mechanical calf-puller.Care should be taken to properly position the calf first. Normal calf presentation and 5 common mal-presentations are shown in Figure 9.

Figure 9. Examples of some common calf presentations.


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The following suggestions are made for dealing with these presentations:

9A If the calf is positioned correctly and dystocia is due to the large size of calf, the calf can be gentlypulled with the hands grasping both front legs, or using chains or a mechanical calf puller. Always besure to pull the calf at a 60o angle to the rear legs.

9B Push the calf back, carefully bend the legs at the joints and pull as for 9A.

9C This is a very difficult presentation to correct and probably will require caesarian section. Contactveterinarian. If this is not possible, try to push both rear legs well back and clear of the birth canal. Becareful not to tear the uterus wall then proceed as in 9A.

9D This is even more difficult to correct than 9C but if hind feet are not in the birth canal it may bepossible to push calf back and reposition the head between the front feet.

9E This is a comparatively easy delivery. The calf must be pulled backwards and in one single motion.As the calf passes through the pelvis, the diaphragm is constricted and this stimulates the calf to inhaleits first breath. It is therefore critical that this first inhalation occurs when the nose is clear of uterinefluids, otherwise the calf will drown.

9F This is a full breech birth and will require a caesarian section.

There are several variations to these positions. For example, 1 leg presenting, calf upside down, etc. Ifcalf is upside down it should be turned into a normal anterior or posterior presentation and pulled.Failure to turn the calf before pulling will almost certainly cause spinal injury and the calf may be unableto walk, or at best walk with difficulty.

General DO'S and DON'TS at calving

Do be gentle.Do be scrupulously clean. Wash your hands and arms and the cows genitalia before starting to work

and every time the cow defecates. The calf head and the birth passage are made of fragile living tissue.Do recognize your own limitations. If you cannot manage the problem stop before the cow is exhaustedand the genital passage swollen and inflamed. Call your vet.Do use uterine boluses if you have had your hand in the cow.Do make sure the calf gets sufficient colostrum in the first 2 hours after birth.

Don't be in a hurry to interfere.Don't attempt the job without plenty of water and soap.Don't use trucks, tractors or horses for pulling the calf.Don't pull on the calf unless there are three things in the birth canal: two front feet and a head, or twohind feet and a tail.Don't put off calling your veterinarian in the difficult cases.

2) Post-partum losses

a) Inclement weather - losses can be reduced by providing properly bedded open sheds (see Figure 8)or closed calf creeps (see Figure 10).


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Figure 10. Sheltered calf creeps can be mounted on skids and transported to spring pastures to preventcalf loss due to inclement weather.

b) Maternal behavior - particular attention should be paid to the cow and calf during the first two hourspost-partum to ensure that a strong bond has developed. The cows should have cleaned the calf and thecalf should have suckled within this time frame. If the calf has not suckled it should be force fedcolostrum, and if the cow has poor maternal behavior the cow and calf should be confined in a small

pen, indoors if necessary, until the bond has been firmly established.

Heifers with dystocia or poor maternal behavior at their first parturition can be given a second chancebut if this problem persists they should be culled after weaning their second calf.

c) Neonatal calf diarrhea. Calf scours caused by infectious agents such as bacteria (E. coli), viruses(Rota and Corona), and protozoa (Eimeria), and environmental factors (overcrowding, environmentalstress, etc.), are the most common cause of post-partum death of calves. Emphasis should be onprevention rather than cure. Cows should be vaccinated with a vaccine containingE. coli strains andRota and Corona viruses (so that antibodies will be passed on to the newborn calf in the colostrum) sixand three weeks before calving. Cows should be moved to clean pens just prior to calving and cowsand calves should not be crowded together after calving. Cows and calves can be treated with acoccidiostat such as Deccox if coccidiosis is a problem. Cows with calves should be moved to a largercorral or preferably to an adjacent pasture.

Length of the Calving Season

The length of the calving season is directly related to the length of the breeding season, which shouldbe no longer than 42 days if the bulls are turned out 40 days after the first cow calves. Age at weaninghas a direct effect on the weaning weight of the calf. Calves born early in the calving season areheavier than calves born late in the calving season because they are older and gain weight faster (Table14). They gain weight faster because they are better able to use the additional milk that cows willproduce during the flush of spring/early summer pasture growth and because the calves themselves aregrazing this high quality pasture in significant amounts. By the time late born calves are able toconsume large amounts of milk and pasture the quality of the pasture has declined and their weight

gains are therefore less.


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Table 14. Effect of calf age on weaning weight and average daily gain (ADG) to weaning of 8,744calves.

___________________________________________________________________________Weaning Weaning Born in the

No. of Weight Age A.D.G. 1st 2nd 3rdWeaning Wt. Calves (kg) (days) (kg) 20 days 20 days 20 days

___________________________________________________________________________

Top 1/3 2910 189 207 0.76 70% 24% 6%Middle 1/3 2916 173 195 0.64 42% 39% 19%Lower 1/3 2918 137 181 0.58 19% 33% 48%___________________________________________________________________________

Seventy percent of the calves in the heaviest weight group were born within the first 20 days of thecalving period compared to 19% of the calves in the lightest weight group. Calves weaned at 207 daysof age were on average 53 kg heavier than those weaned at 181 days of age. Early calving allows cowsand calves to make better use of high quality spring/early summer pasture and range.

The breeding and calving seasons should therefore be confined to six weeks. In Saskatchewan, the

calving season typically runs from March to the first half of April though many producers have movedto calving as early as mid-January in order to maximize the benefit of putting older calves on thespring/early summer pasture flush. However, these early calving herds require good calving facilities,frequently involving some indoor facilities in case of poor weather during calving. In addition, the costof feeding a lactating cow during winter will increase in comparison to a cow calving in spring. Aconcentrated calving season also shortens the period of supervision and does not interfere with springpreparations for crop and forage production.

Heifers should be bred to calve 3-4 weeks before the cow herd. This is because heifers have a longerpost-partum anestrus period than cows and this allows them a longer period to come into estrus for thenext breeding season when they will be bred with the rest of the cow herd. It also allows a more evencalf weight at weaning because heifers do not produce as much milk as cows and therefore usuallywean smaller calves. The extra time between calving and weaning for calves born to heifers which are

bred before the cows allows these calves more time on pasture to compensate for the lower milkproduction of heifers. Greater calving supervision is necessary for heifers and an earlier calving seasonallows for special supervision of calving heifers. Finally, early calving allows both cows and calves tomake maximum use of the high quality spring-early summer forage on range and pasture.

BREEDING THE FEMALE HERD

Cows and heifers should be on a rising plane of nutrition at the start of the breeding season. This isusually accomplished by placing cows on fresh spring pasture or range. Table 15 shows the differencein pregnancy rate for cows gaining or losing weight between calving and breeding.

Table 15. Effect of weight changes after calving on pregnancy rate.___________________________________________________________________________

Period Percent Cows Pregnant Cows notCalving to After 1st After Breeding showingBreeding Service 20 days 90 days heat (%)

Losing weight 43 29 72 14Gaining weight 60 57 82 0___________________________________________________________________________


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The age of the female beef animal will also affect the length of the post-partum anestrus period. Fewer2-3 year-old animals will return to estrus within 70 days of calving compared with those which are 5years or older. Thus it is important to breed the heifers 2-3 weeks before the cows if they are to be bredwith the cows following the birth of their first calf.

Breeding the Cows

Breeding most commonly commences in mid-June and finishes at the end of July. The length of thecalving interval is a direct reflection of the length of the breeding interval. Cow herds which areallowed long breeding periods will calve over a long period of time while those with a restrictedbreeding period will calve in a more concentrated time period.

A cow has a gestation period of about 283 days which leaves her a maximum of 82 days after calvingto return to estrus before being re-bred. During this time she is also nursing a newborn calf.Attempting to breed a cow within 40 days of calving will meet with limited success because at this timeshe will be in anestrus. Therefore the breeding period should be restricted to 42-45 days with the bullsbeing introduced to the herd 4o days after the first cow has calved. This allows for a short calvingperiod, in which labor can be concentrated and more attention paid to calving management. It also

allows calving to be completed before spring breaking and seeding commences. Table 16 shows acomparisonof data taken from cows bred for 45 days or 90 days.

Table 16. Comparison between 45- and 90- day breeding periods in two 50-cow herds___________________________________________________________________________

Breeding Period45 Days 90 Days

___________________________________________________________________________

Number of Cows Calving 50 42

Calving Interval (days) 46 94Average Calf Age at Weaning (days) 265 223Average Calf Weight at Weaning (kg) 185 154___________________________________________________________________________

The body condition of the cow will also influence her ability to conceive (Table 17).

Table 17. Effect of body condition of cows on percentage showing estrus at different intervals post-calving.

___________________________________________________________________________

Days After Calving40 60 80 90

___________________________________________________________________________

Thin 19 46 62 66Moderate 21 61 88 92Good 31 91 98 100___________________________________________________________________________


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There are only 82 days between calving day and conception day if the cow is to calve every 365 daysso it is essential that the cow is in good body condition after calving in order to produce a calf each year(365 days).

Body condition scoring of cows is an important management procedure to ensure maximumreproductive performance in the cow herd. The following notes are taken from the Alberta Beef Herd

Management Guide and are reproduced in their entirety.


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Breeding the Heifers

Continuous reproductive performance in the beef herd largely depends on the individual reproductivecapabilities of the replacement heifer. Replacement heifers must: 1) reach puberty early and cycle

normally, 2) conceive early in the breeding season, 3) give birth to healthy calves without difficulty and4) demonstrate mothering ability by weaning a calf.

Puberty

The onset of puberty in the heifer is influenced by age, weight and breed. Figure 11 shows the effectof liveweight on estrus in Hereford heifers. Note that estrus incidence increased from about 20 to 80%as liveweight increased from 220 to 250 kg. It should be noted that these data come from Australiabecause there are no comparable data from North America. Because most cattle in Australia are finishedat pasture they have a smaller frame size than cattle of the same breed in Canada where feedlot finishingpredominates. Therefore, heifers in Australia are lighter at puberty than their counterparts in Canada.

Figure 11. The relationship between liveweight and incidence of estrus in Hereford heifers.

Most well managed heifers will reach puberty at 14 to 15 months of age, but there are breeddifferences. For example, Angus and Angus-Hereford cross heifers may reach puberty by 10-12months of age, Herefords may take a little longer (12-13 months) and the larger European breeds suchas Charolais, Simmental etc. may take 12-14 months. However all breeds should be cycling and readyto breed by 15 months. Puberty is also affected by weight-breed interactions (Table 18).


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Table 18. Weight at which 14 to 15 month old heifers show first heat___________________________________________________________________________

Liveweight at first heat(kg)Proportionin heat Angus Hereford Charolais A x H S x B L x B

___________________________________________________________________________

50% 250 270 320 250 295 29565-70% 270 295 330 270 320 32085-90% 295 320 340 295 340 340___________________________________________________________________________

B = Different British BreedsA = AngusH = HerefordS = SimmentalL = Limousin

To be of any value in the cow herd, heifers must conceive early in the breeding season. Becauseheifers take longer than cows to clean and return to a normal physiological state after calving, theyshould be bred 3 to 4 weeks earlier than the cow herd. This will allow them time to cycle with the cowherd during their second breeding (Table 19).

Table 19. Percentage of beef females cycling within a given time after calving___________________________________________________________

Average Number of Days Cows in Heat during the First 20 Days of Breedingbetween Calving and Breeding

__ 5years&older__ ________ 2-3 years___ _____

70 95% 79%50 88% 64%30 70% 32%10 29% 10%

____________________________________________________________

Concentrating the breeding interval is a simple and effective method of increasing weaning weights andreproductive performance. Reproduction is a repeatable characteristic. Heifers that breed and calveearly in their first year will continue to calve and breed early as mature cows. Conversely, heifers thatcalve late will continue to be late calvers. Because of the short time interval between calving and

breeding it is almost impossible to advance the breeding period of an individual cow unless she isallowed to skip a year and this is not an economical proposition.

Data from research in this department indicate that prostaglandin-PGF2 (Lutalyse) can be used tosignificantly reduce the breeding interval in heifers. In that experiment, 116 heifers were exposed to

bulls for 30 days. Half of them were treated with PGF2 and half were not treated. 84% of the treatedheifers conceived within the first 14 days of the breeding season compared with only 56% of the non-treated heifers. Of the heifers that became pregnant in the 30 day breeding period, 94% of the treatedheifers conceived in the first 14 days compared with only 66% of the non-treated heifers. This means it


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is possible to breed heifers before going on to summer pasture and, if chin-ball markers or heat mountdetectors are used on the bulls, all non-bred heifers can be culled before going to pasture. This meansthat valuable pasture is used only for pregnant animals and non-pregnant animals can be fed in a feedlotand finished before the end of summer. It also means that the same bulls could be used for both theheifer and cow herds (provided that the bull is suitable for breeding the heifers) since the heifers will befinished breeding before the cow start breeding. This reduces the total number of bulls required for the

herd.

Not all heifers that are exposed to bulls will conceive so that more heifers than are required forreplacements should be exposed to breeding. If replacement heifers are selected at weaning on an age ofcalf and dam adjusted basis and fed to gain 0.7 kg/day, they should reach their target weight forbreeding (Table 18) at 15 months. The number of extra heifers can then be kept to a minimum. Theformula for calculating the adjusted weaning weight of calves is as follows:

Adjusted weaning weight = {[(ww bw) / aoc] * acf * csf} + bw

Where ww = weaning weight of calf bw = birth weight of calf

aoc = age of calf at weaningacf = age of cow factor (Table 20)csf = calf sex factor (1.0 for males and 1.05 for female calves)

Table 20. Adjustment factors designed to equate performance of all calves to a level equal to thatexpected from a mature dam.

Age of Dam (years) 2 3 4 5 6 7

Age of Cow Factor 1.18 1.09 1.04 1.02 1.01 1.00

Heifers should be bred to young performance tested bulls which had a relatively low birth weightbecause this trait is highly heritable. This practice tends to reduce calving difficulties and increases therate of genetic improvement in a herd. Young bulls are lighter than mature bulls and the chances ofinjury at the time of breeding are reduced. If heifers are being bred by means of artificial inseminationthe sire should be proven for ease of calving. Whatever the breeding scheme, the reproductive tract ofheifers should always be examined to ensure that it is functioning normally prior to breeding.

Bull to Cow Ratios

The number of cows that a bull can successfully service during the breeding season depends on the

nature of the breeding pasture, the physical condition of the bull and the amount of time allowed forbreeding.A bull may be able to successfully impregnate up to 50 cows or more where the breeding isconfined to small pastures. However, under open range conditions, where the terrain is rough and thecows distributed over a relatively large area, the same bull may breed only half this number of cows.As a general rule of thumb, the bull-cow ratio should be 1:25 on relatively open range and 1:20 onrough or heavily forested ranges. Yearling bulls should be allotted around 20 cows per bull on goodopen range and 10 to 15 cows on rough range.

On ranges where accessibility is not a problem, bulls can be rotated through the breeding herd. Bulls


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that dominate the breeding, or bulls which spend all their time intimidating and fighting other bulls canbe removed for short periods. This practice also accommodates efficient use of yearling bulls byallowing for rest periods.

Confinement Breeding

This refers to the breeding of cow and/or heifers in corrals or small breeding pastures at home beforegoing on range. The advantages are:

1) Can use a restricted breeding period more effectively (e.g. synchronization of estrus).2) Require fewer bulls.3) Can use Artificial Insemination.4) Reduces problems of bulls on range, i.e. broken fences, death from poisonous plants, etc.5) Reduces the possibility of cows being bred by a neighbor's bull.6) Can identify non-breeders using chin-ball markers or heat mount detectors.

The disadvantages include:

1) Higher cost of feeding.

2) Requires an early calving (mid to late winter) if cows are to be bred before going on to summerpasture. This may increase calving mortality as the risk of inclement weather during calving is high.

Fall Calving

This refers to breeding in the winter to calve in the fall.

Advantages of fall calving

1) Calf can be weaned in the spring and placed on lush spring pasture. Good gains on pasture can putthe animal in the feedlot as a short keep animal the following fall.

2) Fall weather may be more reliable than spring weather.

3) More convenient timing in terms of labor commitments (i.e. harvest is over so 100% of time can bedevoted to calving).

4) Can use AI more readily because cows are usually in confined areas at breeding time.

5) May alleviate a calf scours problem. Scours are more prevalent in the winter/spring than fall.

Disadvantages of fall calving

1) Feeding of conserved feeds occurs when the cow has its peak requirements for quality and quantityof feed due to lactation so feed must be abundant and high quality, hence expensive.

2) Breeding occurs during the winter when bulls are the least active reproductively.

3) Confined calves generally don't grow as well as free ranging calves probably due to additional stressof clinical and sub-clinical disease and a reduced milk production of cows during winter as comparedwith spring/summer. Thus ADG and weaning weight of fall calves are normally less than in springcalves.

4) Calves must be creep-fed during the winter to avoid competing with the cows for feed.


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Standing heat lasts for about 18 hours. With heifers, this may be a few hours less. The best time tobreed a cow is four to six hours prior to ovulation. This occurs about ten to twelve hours after standingheat. Sperm must mature in the reproductive tract of a cow for four to six hours before they are capableof fertilizing an egg. The egg will remain viable for six to eight hours. Cows should therefore be bredat the end of standing heat and not later than twelve hours after standing heat.

Pregnancy Testing

All female cattle should be pregnancy tested in the fall by a veterinarian. Some producers also becomevery proficient in the technique of pregnancy testing by rectal palpation. It is usually not an economicproposition to carry open cows for 18 months before they produce another calf. The economic benefitsof selling an open cow in fall compared with feeding her through winter and selling her in spring whenshe fails to calve are shown in Table 21. The benefits, which are net of costs, increase with increasingherd size and decreasing pregnancy rates. The data in Table 10 are the results of a 10-year study inSaskatchewan.

Table 21. Economic Benefit of Pregnancy Testing ($)

__________________________________________________________________

40 Head Herd 100 Head HerdPregnancy Rate (%)

93 80 93 80

Per open cow ($) 21.36 46.93 41.74 54.06Per cow ($) 1.50 9.39 2.92 10.81Per herd ($) 59.82 375.42 292.15 1018.15

MANAGEMENT OF BULLS

A bull has two functions in a breeding herd: (i) to impregnate cows and heifers and (ii) to pass on hisgenes to his progeny. Therefore he must be fertile, have high libido, be free from any physical defectswhich might prevent him from breeding and have whatever genetic traits are seen as desirable in theparticular herd. Puberty in bulls is influenced by the same three factors that influence puberty inheifers, i.e. age, weight and breed.

Sperm Production

The production of large volumes of high quality sperm is dependent on normal scrotal and testiculardevelopment. For best sperm production the testicles need to be maintained at a temperature slightlylower than body temperature. The scrotum must be shaped to allow the testicles to move closer to thebody during cold environmental temperatures and further away from the body during hot temperatures.The following diagrams Figure 12) illustrate the three more common scrotal shapes found in bulls.


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Figure 12. Different shapes of the scrotum in bulls.

The middle bull has a full, well suspended scrotum with a well developed neck which willaccommodate easy movement of the testicles. The shape of the scrotum of the bull on the left is muchstraighter and does not allow for the same degree of testicular temperature regulation as the neckedscrotum. The bull on the right has a very tight scrotum. Generally, bulls with this type of scrotum, arenot good semen producers. The testicles cannot descend low enough to offset increasing temperatures

and sperm production is suppressed.

The volume of semen produced is related to the growth and development of the testes. Every bullshould be examined for testicular development. The testicles should be large, firm and even in size.Testicles which are soft and mushy or small and hard indicate that the animal may have had an infectionor injury. The cord suspending the testicles should be firm and the epididymis should be soft andpliable. The sheath area should be firm but pliable and free from infection and hair rings.

Scrotal circumference is a good indication of testicle size and volume of sperm production but averagescrotal circumference (measured by drawing both testicles into the scrotum and measuring with a metaltape) varies with breed (Table 22). However, the greater the scrotal circumference, the greater thenumber of sertoli cells and hence spermatozoa.

Table 22. The effect of breed on scrotal circumference (cm) in bulls.__________________________________________________________________________

Age AgeBreed 1 year 2 years___________________________________________________________________________

Simmental 35.9 38.7Aberdeen Angus 33.8 37.1Maine Anjou 33.6 36Charolais 32.9 36.3Horned Hereford 32.8 36.1Shorthorns 32.4 34.9Polled Hereford 32.2 35.6

Blonde 30.6 35.6Limousin 30.3 32.1___________________________________________________________________________

Studies have shown that scrotal circumference (SC) in 2 year old bulls can vary from 19 to 47 cm. Of444 bulls tested in one experiment, all bulls with SC < 30 cm had poor quality semen compared withonly 4% of bulls with SC > 30 cm. Scrotal circumference and sperm production are highly correlatedand bulls with large testicles can be successfully bred to more cows than bulls with small testicles(Table 23).


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Table 23. Heifers which conceived at first service when bred at two bull:heifer ratios to bulls withvarious scrotal circumferences.___________________________________________________________________________Bull Scrotal Bull:Heifer Ratio

Circumference 1:60 1:75

(cm) % Pregnant___________________________________________________________________________27 22 1030 44 4331 55 -32 68 4633 71 5834 72 -35 83 6136 62 5237 74 5338 - 63

_________________________________________________________________________________

Scrotal circumference is highly heritable and is positively correlated with growth rate and live weight.Feeding between 6-13 months is also very important. Testicular growth is very rapid around pubertyand poorly fed bulls achieve slow testicular growth and have smaller testicles at maturity than bullswhich are well fed around puberty.

The following diagram (Figure 13) illustrates the correct method of measuring scrotal circumference.

Figure 13. Correct measurement of scrotal circumference in a bull.

The breeding soundness evaluation involves the measurement of scrotal circumference (40% ofevaluation), and the drawing of a semen sample for evaluation of sperm morphology (40%) andmotility (20%). The evaluation system is shown in Table 24.


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Structural soundness

The structural soundness of a bull is most important. The bull carries a lot of weight on its legs and ifthey are not sound he will be less active in seeking and mounting cows in heat. When he mounts, hisweight is carried on his rear legs. The following diagrams (Figure 14) show desirable and undesirablecharacteristics of front and rear legs.

Figure 14. Desirable and undesirable characteristics of the feet and legs of bulls.

Bull Selection Criteria

The selection of a herd bull is very important because a good bull will be expensive but he will pass hisgenes to his progeny. There will always be preferences based on breed and other characteristics such ashorned or polled, color and markings. However, the following criteria are applicable to all bulls:

i) Low birth weight relative to the breed averageii) High average daily gain relative to the breed averageiii) Good breeding Soundness Evaluationiv) Sound feet and legsv) Good libidovi) Good behavior (sexual and non sexualvii) Good conformationFeeding Young Bulls

The factors that influence puberty in bulls are the same as those for heifers. It is important that younggrowing bulls be well fed but not overfed. Too much concentrate (grain) in the ration can permanentlydamage the fertility of a bull. In an experiment at the Agriculture Research Station, Lethbridge, bullswere fed a high or a medium energy ration. The high energy ration (HE) consisted of 80% concentrate


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than steers. Stress causes the animal to deplete is reserves of muscle glycogen and this decreases theamount of lactic acid formed in the muscle post-mortem. Bright red meat has a pH 5.9 because of the lack ofglycogen at slaughter and hence post-mortem lactic acid.

The younger the animal at castration, the less stress it experiences. However, if the calf is 6-9 months at

castration the stress is short term and rarely affects weight gains. On the other hand animals castrated atan early age do not benefit from the higher growth rate of entire animals. This can be corrected with theuse of anabolic implants (see section on Implanting). There are several methods of castration.

a) Surgical castration - Requires a sharp knife and preferably an emasculator which will crush and cutthe cord with little bleeding. The scrotum should be cleaned with disinfectant and the instrumentswashed with disinfectant between each castration. The incision should be large and allow adequatedrainage. The use of an antibiotic powder or spray and insecticide spray will reduce the risk ofinfection. Healing should be complete in 3-4 days. Calves should not be castrated on hot days whenbleeding will be increased, on dry, dusty days or when there are a lot of flies when the risk ofinfections will increase.

b) Bloodless castration - The advantages of bloodless castration are a reduction in the risk of infection

from flies, dust, etc. and it can therefore be performed at any time. There are several methods.

(i) Burdizzo - this is a large emasculator which crushes the cord by external application requiringno incision. One testicle is crushed at a time and the testes degenerate and atrophy due to lack of bloodsupply. Improper application will lead to stags.

(ii) Elastrator rings - these are tight rubber rings placed over the scrotum above the testicles whichcuts off the blood supply and the scrotum degenerates and sloughs off. It is important to trap bothtesticles and if the blood supply is not completely cut off, the scrotum will swell and become painful.This method can only be used in young calves.

Other methods of bloodless castration have been tried but with limited success. These include

(iii) Chemical castration - In 1984 a product, CHEMCAST, was released on the Canadian market.The product has been withdrawn by the manufacturers although research in this department during1984 and 1985 indicated that the product was 90% efficacious if used properly. The chemical waslactic acid and was injected into each testicle. The testicles swell to about twice normal size and thendegenerate and atrophy. Care had to be taken to inject directly into the testicle. Widespread misuseprompted the withdrawal of the product from the Canadian market. Chemcast is still registered inCanada and USA for use in calves up to 70 kg liveweight but research in this department indicated thatgood efficacy was possible in calves up to 200 kg provided the dose rate was increased in proportion tothe weight of the calf.

(iv) Immuno-castration involving immunization of an animal against producing its owngonadtrophic releasing hormone (GnRH) has receiving considerable research attention but the efficacy

of this method has been disappointing.Branding

The brand identifies ownership of the cattle and must be registered with Provincial Government BranchInspectors. It is still the only legal identification of ownership. There are several methods of branding:

a) Fire branding - The iron is heated in a fire or electrically and placed on the skin. Care must be takennot to burn too deep but to scar the skin with a burn welt that prevents hair re-growth. Moderatepressure is required for successful branding. Fire branding damages the hide and this cost the


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Canadian beef industry $3.56/head or a total of $9.6 million in 1996. Other forms of branding havetherefore been tried in an attempt to reduce this loss.

b) Cryogenic branding - The branding iron is cooled in liquid nitrogen and the brand causes themelanocytes to produce colourless hair. This method therefore cannot be used on white cattle (i.e.Charolais). The advantage is that it does not damage the hide but needs skill and a source of liquid

nitrogen which is expensive. For these reasons it is not widely used in the industry.

c) Electronic branding - Implantation of a small electronic CHIP in the ear (or brisket) containing IDinformation is being investigated as a means of ownership identification but current problems includerejection of the implant and risk of removal of the implant.

Vaccinations

The prevention of production losses through death or reduced weight gains in the calf as a result ofdisease is critical to the profitability of a cow/calf operation. There are a number of diseases that can beprevented through the appropriate use of vaccines.

1) Clostridial diseases (Blackleg, tetanus, malignant edema, enterotoxemia, septicemia, gangrene). All

calves should be vaccinated at 6-8 weeks of age and again 6-8 weeks later. Various combinationvaccines are available which provide protection against up to 8 Clostridia spp.

2) Infectious Bovine Rhinotracheitis (IBR) and Parainfluenza (PI3). These are viral diseases related tothe herpes virus that become life threatening in association with Pasterella spp. Causing respiratorydistress, pneumonia and death, particularly in cattle shipped to a feedlot (shipping fever). There is acombined vaccine for this disease complex which can be administered intra-nasally and should begiven 2-4 weeks before weaning because stress caused by weaning is a contributing factor in theoutbreak of respiratory disease.

3) ITEME (infectious thromboembolic meningoencephalitis) is a disease caused by Hemophilussomnus which can be prevented with the use of a vaccine. The disease is more common in feedlotcattle, particularly in association with shipping fever and is characterized by Fever, depression,

ataxia(muscular incoordination), blindness and coma. Death can occur quickly, with 1 hour to severaldays.

Preconditioning

Preconditioning is a program designed to reduce the stress inflicted on an animal that is weaned andshipped directly to a feedlot. In this situation severe stress is caused by weaning, crowding of animalstogether, transport to sale, exposure to infective agents at auction sales, transport to the feedlot andadjustment to new feeds, feeders, waterers, confinement and so on.

Preconditioning requires that animals be identified, dehorned, castrated, immunized for clostridia, IBR,PI3 and ITEME, weaned and on feed and treated for warbles. A veterinary certificate accompanies pre-

conditioned cattle. For its success, the program depends upona) the issuing of a certificate as formal documentation

b) the holding of special pre-conditioned calf sales

c) the willingness of buyers to pay about $0.10/kg premium to cover costs

The advantages are:


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i) The cow/calf operator sells a better calf and builds a reputation which attracts premium prices.

ii) The feedlot operator loses fewer calves from shipping fever.

Survey results from Alberta indicated that the average premium paid was $0.11/kg for steers and $0.09for heifers. The average cost of preconditioning was $49.49/calf, ADG during the preconditioning

period was 0.89 kg/d and the average return NET of costs was $54.23/calf. However the program wasnever very popular in Saskatchewan and preconditioned calf sales were abandoned some years ago butthe program still exists in Alberta.

7. Backgrounding

In the cow/calf sector, this usually refers to the holding over of calves after weaning and feeding themduring their first winter to gain 0.2-0.3 kg/day. These calves are then placed on pasture in springwhere they make rapid compensatory growth and are usually removed from pasture in mid-summer andfinished on a high grain diet as short keep animals (60-80 days). In the feedlot sector, backgroundingusually refers to the feeding of calves for the first few months after entering the feedlot on a high forageration to gain 1-1.5 kg/d.

8. Implanting

At present, Ralgro and Synovex C are registered for use in suckling steers and heifers. Compudose isregistered for use in steers only. Calves can be implanted at birth and, in experiments in this departmentheifer calves implanted at birth and 100 days later weighed 23 kg heavier than unimplanted calves atweaning, but there was no advantage to implanting bull calves. The advantages of implanting malecalves increase with early castration. Ralgro is not registered for use in calves being kept for breeding.The effects on bulls are clear. For example research in this department indicated that testicles from bullcalves castrated at 5 months of age weighed 9l g for unimplanted calves compared with only 29 g forimplanted calves. The effects of implantating heifers at birth are also clear. Resarch also in thisdepartment has consistently shown that conception rates in heifers implanted at birth is only 40-45%.However, implanting at 60 days has shown no detrimental effects but a `safe' age between birth and 60days has not been demonstrated. Meanwhile, however, it is recommended that heifers not be implanted

if they are to be kept as replacements after weaning.

Parasites

(i) Warble grubs - these are the larvae of the gad fly which cause economic loss by damage to the hideand decrease weight gains during migration. Migrating larvae bore through the hide on the animal'sback causing abscesses and secondary infections. They can be controlled by annual applications ofsystemic insecticides (Ivomec, Spotton, Neguvon, Cyclectim) which kill the migrating larvae. Controlshould not be attempted after the end of November as at this time larvae may be migrating in the spinalcanal and their death there can cause inflammation of the spinal cord resulting in inco-ordination of thehind quarters.

(ii) Lice - These are readily controlled by the same systemic insecticides that control warbles.These occur through the winter.

(iii) Flies - Flies can be a major problem for cattle on pasture and can result in considerable weightloss due to irritation and loss of grazing time. They can also cause blood loss in the order of 300ml/day. Weight loss can also lead to reproductive loss. There are three main fly problems:

1) Face flies - these may be associated with the transmission of pink-eye.

2) Horn files - these feed by sucking blood from cattle and there-by causing irritation and loss of


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grazing time. They are the most prevalent fly in Southern Saskatchewan.

3) Black flies - these are also a biting fly and reduce productivity by reducing grazing time, weightgains and reproductive rates. They are most prevalent in Northern Saskatchewan.

One estimate has suggested that the above flies are responsible for 6.5 x 106 kg of weight loss in

cattle in Canada (Haufe 1981). In Saskatchewan in 1979, black flies were estimated to be responsiblefor a $2.9 million loss to the beef industry.

Control can be achieved by spraying cattle with an insecticide (e.g. Malathion), using oilersimpregnated with with insecticide in diesel fuel or spraying water with larvicide for black fly control orby applying insecticide impregnated ear tags (Bovaid, Debantic, Permectrin, etc.) to cattle. The lattermethod has received most support and attention since 1981 but some recent reports suggest that someimmunity may be building up in the fly population.

Younger cattle are most seriously affected by fly irritation so earlier breeding and calving will helpreduce losses as bigger calves cope better.

Weaning

Proper weaning procedures can reduce the stress of weaning resulting in less disease and the preventionof weight loss at weaning. The following is a recommended check list for weaning:

1. Keep pre-weaning handling stress to a minimum2. Get medical supplies in advance3. Give all vaccinations and boosters prior to weaning if possible or time first vaccination so that booste

is given at weaning4. Treat for grubs and lice before weaning5. Castrate and dehorn at least 3 weeks before weaning6. Provide creep feed at least 2 weeks before weaning7. Wean according to weather not date - wean at least 3 weeks before cold weather to reduce pos

weaning respiratory problems

8. Put all cows and calves in weaning pen 2-3 days before weaning then remove cows not calves9. Move cows far enough from calves to minimize disturbance10.Provide high quality feed (hay, minerals & vitamins in a grain carrier) and good water11. Allow adequate bunker space for all calves to feed together (18-22 ins/calf)12.Observe calves twice daily for signs of sickness13.Separate sick calves14.Make feed changes gradually15. Remove stale feed from bunkers

An alternative to 8 and 9 is to wean with fence-line contact between the cows and calves. In anexperiment comparing fence-line weaning with remote weaning, calves that were fence-line weaned had

an ADG of 1.66 kg/d compared to 0.74 kg/d for remote weaned calves but only for the first 3 days.This effect diminished gradually and there was no difference in the overall ADG of the of the 2 groupsin the 28 day post-weaning period. It should also be noted that in that experiment, item 8 above was notpracticed and the remote group was separated when the calves were placed in the weaning pen.


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MANAGEMENT RECORDS

Keeping good records is essential to good management. All cows and calves should be indentified andear tagged and, if possible, weighed and condition scored at birth and weaning. There are a number ofrecord-keeping software programs available through the various breed societies, government agenciesand agricultural software developers. Advanced computer users can develop their own record keeping

systems using database software packages such as FileMaker, FoxBase etc.

Grazing animal nutrition.pdf

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