The Estrous Cycle in Cattle
Transcript of The Estrous Cycle in Cattle
![Page 1: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/1.jpg)
The Estrous Cycle in Cattle
Physiology and Endocrinology
1
![Page 2: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/2.jpg)
Overview
• Estrous cycle• Synchronization and benefits• Selecting hefers
– RTS– Conditioning
• Products and prices• Summation
![Page 3: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/3.jpg)
Estrous Cycle
Length of the estrous cycle Average 21 days (range 18 to 24 days)
Estrus (standing heat) 12 to 18 hours (range 8 to 30 hours)
Ovulation Approximately 30 hours after the beginning of
standing heat (or 12 to 18 hours after the end of standing heat)
2
![Page 4: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/4.jpg)
Estrous Cycle
Major structures on the ovary are …
Follicle … a blister-like structure containing the egg (referred to as oocyte); produces hormone “estrogen” High amount of estrogen causes “standing heat” and
“ovulation”
Corpus luteum (referred to as “CL”) … looks like a hard yellow structure and produces hormone “progesterone” that is responsible for maintenance of pregnancy
3
![Page 5: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/5.jpg)
Follicle DevelopmentFollicular Wave
Recruitment
Growth
Selection
Dominance
Regression
Next Recruitment
Follicle development occurs as a wave-like pattern consisting of “Recruitment”, “Selection”, “Growth”, “Dominance”, and “Regression” phases Usually 2 to 4 follicular waves occur during the estrous cycle in cattle
4
![Page 6: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/6.jpg)
Follicle DevelopmentFollicle Stimulating Hormone (FSH)
Recruitment
Next Recruitment
FSH precedes recruitment of follicles (causes follicles to start growing) FSH is the same hormone used for superovulation and embryo transfer in cattle
5
Regression
FSH FSH
![Page 7: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/7.jpg)
Follicle DevelopmentLuteinizing Hormone (LH)
Growth
Selection
Dominance
LH promotes further follicle growth and maturation of egg
6
Regression
LH pulses
![Page 8: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/8.jpg)
Follicle Development and OvulationLuteinizing Hormone (LH) and Estrogen
Growth
Selection
Dominance
Estrus
LH Surge
Ovulation
Estrogen
LH stimulates follicle growth and a growing follicle produces high levels of estrogen High levels of estrogen, in turn, cause estrus and surge release of LH that triggers ovulation
7
![Page 9: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/9.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Length of the estrous cycle in cattle with 3 follicular waves is typically 20 to 24 days
Follicle Development During the Estrous Cycle
Example for 3 Follicular Waves8
Ovulation
Ovulation
![Page 10: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/10.jpg)
Day of the Estrous Cycle0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Length of the estrous cycle in cattle with 2 follicular waves is typically 18 to 20 days, slightly shorter than the estrous cycle with 3 follicular waves
9
Ovulation
Ovulation
Follicle Development During the Estrous Cycle
Example for 2 Follicular Waves
![Page 11: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/11.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
10
Ovulation
Ovulation
Endocrinology During the Estrous CycleFollicle Stimulating Hormone (FSH)
Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
FSH
![Page 12: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/12.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
11Endocrinology During the Estrous CycleLuteinizing Hormone (LH)
LH SurgeOvulation
Ovulation
LH Surge
LH pulses LH pulses
![Page 13: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/13.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
12
Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
Endocrinology During the Estrous CycleEstrogen
Ovulation
Ovulation
Estrogen
![Page 14: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/14.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
Growth
Regression
13Corpus Luteum (CL)Growth and Regression
Corpus luteum develops from the ovulated follicle and takes approximately 10 days to reach mature size
Ovulation
![Page 15: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/15.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Corpus luteum produces progesterone Progesterone is responsible for maintenance of pregnancy after conception occurs
14Corpus Luteum (CL)Progesterone
Growth
Regression
Progesterone
![Page 16: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/16.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Corpus Luteum (CL) RegressionProstaglandin F2 (PG)
Day of the Estrous Cycle Late in the estrous cycle, uterus produces PG which causes regression of corpus luteum PG is the same or similar hormone in “Lutalyse®”, “Estrumate®”, “ProstaMate®”, and “In Synch®”
Growth
Regression
15
PG
![Page 17: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/17.jpg)
Estru
s
Corpus Luteum (CL) MaintenanceWhen cow becomes pregnant …
Day of the Estrous Cycle
Presence of embryo blocks uterus to produce PG late in the estrous cycle which causes maintenance of corpus luteum and production of progesterone for pregnancy
PG
Maintenance
0 2 4 6 8 10 12 14 16 18 20 0
Embryo
Growth
16
![Page 18: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/18.jpg)
Progesterone regulates LH PulsesLuteinizing Hormone (LH)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
LH Surge
Progesterone regulates secretion pattern of LH pulses and hence, follicular development
17
Progesterone
LH pulses LH pulses
![Page 19: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/19.jpg)
Endocrinology of the Estrous Cycle
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
Estrogen
Progesterone PG
Relationships among estrogen, progesterone, and PG during the 21-day estrous cycle
18
![Page 20: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/20.jpg)
Physiology and Endocrinologyof the Estrous Cycle
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
19
Relationships among structural and hormonal changes during the 21-day estrous cycle (example shown for cattle having 3 follicular waves)
![Page 21: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/21.jpg)
Estrus Synchronization
20
![Page 22: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/22.jpg)
Effective Estrus Synchronization Programs
Shorten the AI breeding season Cows or heifers are in estrus during a
predictable interval that facilitates AI
Reduce time and labor required to detect estrus
Result in more cows and heifers becoming pregnant early during the breeding season Progestin-based programs can induce estrous
cyclicity in anestrous cows and prepubertal heifers (For example: MGA, or CIDR)*
21
* Progestins are progesterone-like compounds that act like progesterone
![Page 23: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/23.jpg)
Effective Estrus Synchronization Programs
Result in older and heavier calves at weaning
Will have beneficial effects on the next breeding season
More cows and heifers calve early More days postpartum at the next breeding
season Replacement heifers will be older
22
![Page 24: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/24.jpg)
Effective Estrus Synchronization Programs Consider what happens during a restricted breeding
season, based on the average 21-day estrous cycle:
If cows or heifers are cycling when an estrus synchronization treatment is implemented and they exhibit estrus during the synchronized period, they would have 3 opportunities to conceive during a 45-day period or 4 opportunities during a 65-day period
If cows or heifers are cycling but no estrus synchronization treatment is implemented, then they have only 2 (45-day) or 3 (65-day) opportunities to conceive
If cows or heifers are not cycling at the beginning of the breeding season, they have even less opportunity to conceive
23
![Page 25: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/25.jpg)
Points to Consider When UsingEstrus Synchronization
Estrus synchronization is never a substitute for:
Nutrition Herd health Proper management
Estrus synchronization should not be used as a crutch for poor management
When administered appropriately, estrus synchronization is an effective reproductive management tool that can be used to facilitate AI
24
![Page 26: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/26.jpg)
Determine which females would make the best candidates before beginning estrus synchronization
Successful application of estrus synchronization is easier to accomplish with heifers (no calves to work with)
Points to Consider When Using Estrus Synchronization
25
![Page 27: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/27.jpg)
Selecting Heifers for Estrus Synchronization
Heifers should be of adequate age (cycling or close to reaching puberty)
Heifers should be of adequate weight Developed to 65 % of projected mature
weight Do you know the mature weight of your
cows?
Utilize reproductive tract score (RTS) to assess reproductive maturity
37
![Page 28: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/28.jpg)
Timing of Puberty in Heifers
Target weight: Heifers reach puberty at approximately 65% of their mature body weight
Determine your desired weight at breeding, calculate the gain needed to meet that weight, and feed to meet it
38
![Page 29: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/29.jpg)
Management Considerations for Heifers
DO NOT use growth promoting implants in replacement heifers
Implants may disrupt or impair normal development of reproductive organs Developing uterus is especially sensitive to
growth promoting implants
39
![Page 30: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/30.jpg)
Management Considerations for Heifers
Reproductive Tract Scores (RTS) are determined by rectal palpation of the ovaries and uterus
The RTS should be performed approximately 6 to 8 weeks prior to breeding season and/or approximately 2 weeks prior to beginning an estrus synchronization treatment
40
![Page 31: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/31.jpg)
Reproductive Tract Scores (RTS)
RTS
1
2
3
4
5
Uterine hornsImmature
< 20 mm diameterNo tone
20-25 mm diameterNo tone
20-25 mm diameterSlight tone
30 mm diameterGood tone
> 30 mm diameter
Length
15
18
22
30
> 32
Height
10
12
15
16
20
Width
8
10
10
12
15
Ovarian Structures
No palpable follicles
8 mmfollicles
8-10 mmfollicles
> 10 mm follicles
CL possible
CL present
Ovarian Measurement (mm)
Adapted from Anderson et al., 1991
Description
Infantile
Prepubertal(more than 30
days to puberty)Peripubertal(within 30 days
to puberty)
Cycling(Follicular Phase)
Cycling(Luteal Phase)
41
![Page 32: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/32.jpg)
RTS Measurements
RTS12345
No. ofHeifers
61278
1103494728
Weight (lb)594a
620b
697c
733d
755d
Pelvic Width (cm)10.9a
11.2a
11.4b
11.7c
11.7c
Pelvic Height (cm)13.9a
14.1a
14.5b
14.7c
14.7c
Pelvic Area (cm2)152a
158a
166b
172c
172c
Estrous Response
54 %a
66 %b
76 %c
83 %d
86 %d
Adapted from Patterson et al., 1999a
42
Note the relationship between increasing RTS, weight, and skeletal development determined by pelvic area Estrous response increased among heifers that were more reproductively mature at the beginning of estrus synchronization and/or breeding season
a, b, c, d = P < 0.05
![Page 33: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/33.jpg)
Relationship Between RTS and Pregnancy
RTS12345
No. ofHeifers
53762
345833982613
Pregnant31
610301430062331
Open22
152444392282
Pregnancy Rate58 %80 %87 %89 %89 %
Randle et al., 2001
43
Higher pregnancy rates at the end of the breeding season were achieved among heifers that were more reproductively mature at the beginning of estrus synchronization and/or breeding season
![Page 34: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/34.jpg)
Prepubertal Anestrus Timing of puberty is controlled by …
Age Weight Breed Season
Develop heifers to approximately 65% of mature weight by the breeding season
This will help them to attain puberty at the right time
53
Many factors involved
![Page 35: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/35.jpg)
55Nutritional Anestrus
Nutritionally stressed cattle will experience delays in return to estrus after calving
Can be “managed” through
Improvement in BODY CONDITION Proper feeding management
![Page 36: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/36.jpg)
56Postpartum AnestrusInduction of Estrous Cyclicity
Bull exposure Prepubertal heifers
Exposure of prepubertal heifers to sterile bulls (for example, vasectomized, epididyectomized … etc) for 60 to 80 days before the breeding season may hasten the onset of puberty (ranges from no effect to 70 days earlier)
This procedure also shortens the postpartum period in anestrous cows however my concentration is on heifers
Izard and Vandenbergh, 1982; Berardinelli et al., 1978;MacMillan et al., 1979; Roberson et al., 1991
Foote, 1974; MacMillan et al., 1979; Zalesky et al., 1984; Gifford et al., 1989
![Page 37: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/37.jpg)
Products Currently Utilized in Protocols to Synchronize Estrus
*** Price may vary depending on suppliers ***
Prostaglandin F2 (PG) Lutalyse®, Estrumate®, ProstaMate®, In Synch®
Approximate cost is $3.00/dose (range $2.50-$4.00) Gonadotropin-Releasing Hormone (GnRH)
Cystorelin®, Factrel®, Fertagyl®
Approximate cost is $5.00/dose (range $4.00-$6.00)
Melengestrol Acetate (MGA® Premix) Approximate cost ranges $0.14 - $0.40/day/head including
carrier 14 days ($2.00-$5.60/head) or 7 days ($1.00-$2.80/head)
EAZI-BREED™ CIDR® Cattle Insert (CIDR) Approximate cost is $8.00 (range $8.00-$10.00)
Syncro-Mate-B® (off the market)
28
![Page 38: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/38.jpg)
Prostaglandin F2 (PG)
60
![Page 39: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/39.jpg)
PG causes CL regression
No effect on anestrous cattle
No induction of estrous cyclicity … No Jump-start
Only effective during Days 6 (6 days after estrus) to 16 of the estrous cycle
Prostaglandin F2 (PG)
61
Lauderdale, 1972
![Page 40: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/40.jpg)
0 2 4 6 8 10 12 14 16 18 20 0
Day of the Estrous Cycle
PG regresses CL
NO NO
YES
Prostaglandin F2 (PG)
Estrus Estrus
62
![Page 41: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/41.jpg)
Modified from Stevenson et al., 2000
Hours following second PG injection
% o
f cow
s in
estru
s
0
10
20
30
40
50
0 < 24 36 48 60 72 84 96 108 120 > 120
PG
2 x PG
77Estrous ResponseDouble Injection PG Program
Example shown is 14-day interval for PG injections
![Page 42: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/42.jpg)
Advantages: Cost effective ($3.00 or $ 6.00) Easy to use Good fertility
Single or Double Injection PG Programs
$3.00 or $6.00 ($3.00/one dose)
74
![Page 43: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/43.jpg)
Disadvantages: No effect between days 0 to 4 or 16 to 21 of the
estrous cycle Improved effectiveness after day 10 of the
estrous cycle Require heifers and cows to have CL (cycling) Require extensive estrus detection (minimum
7 days) No induction of estrous cyclicity
(No Jump-start)
Single or Double Injection PG Programs
$3.00 or $6.00 ($3.00/one dose)
75
![Page 44: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/44.jpg)
Estrous response: Varies depending on the degree of estrous cyclicity
in the herd and the stage of the estrous cycle of an individual animal
Single injection of PG … up to 40 to 60 % Double injection of PG … up to 50 to 80 %
Timing of estrus: Before PG injection to 7 to 10 days after PG
injection Peak response ranges from 48 to 96 hours after PG
injection
Possible OutcomesSingle or Double Injection PG
Programs
76
![Page 45: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/45.jpg)
Melengestrol Acetate (MGA®)
98
MGA is a registered trademark of Pfizer Animal Health
![Page 46: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/46.jpg)
Orally active progestin, administered as a feed additive
Blocks estrus and ovulation Acts similar to progesterone from CL
MGA can induce estrous cyclicity in peripubertal (within 30 days to attain puberty) heifers and postpartum anestrous cows
Currently, MGA and CIDR are the only progestins commercially available in the U.S.
Melengestrol Acetate (MGA)99
Patterson et al., 1989
![Page 47: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/47.jpg)
Mix with grain source (example: cracked or ground corn) For example: MGA with ground corn ($0.15/day/head) Top dressing does not work well
If cattle are on lush pasture, remove salt from pasture and include salt in MGA carrier
0.5 oz. Salt per cow and MGA in carrier ($0.30/day/head)
Pellet form (very palatable) For example: MFA Cattle Charge® with MGA ($0.40/day/head)
Intake ConsiderationsWhat type of carrier to use?
100
![Page 48: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/48.jpg)
Need to provide adequate bunk space (18 inches per heifer, and 24 inches per cow)
Make sure cattle come to bunk before start of feeding MGA If cattle are not used to bunk feeding, 1-2
weeks of warm-up bunk feeding is recommended
MGA should be fed one time per day at approximately the same time every day
Separate heifers from cows for MGA feeding Late-term pregnant cows should not be fed
MGA
Intake Considerations101
![Page 49: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/49.jpg)
• MGA can be combined with PG to improve results
![Page 50: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/50.jpg)
Distribution of Estrus
MGA-PG
(for AI)
MGA only(for Natural service)
% ofherd in estrus
Adding the PG injection to the MGA program results in a much tighter synchronization of estrus
3-5 days
7-10 days
106
Adapted from Patterson et al., 2000
![Page 51: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/51.jpg)
Management ConsiderationsWhy Not Introduce Bulls Right After MGA
Withdrawal?
0 5 10 15 20 25 30
Days after MGA feeding
% ofherd in estrus
If bulls were introduced to the herd right after MGA withdrawal, they may be overworked during the less fertile estrous period after MGA withdrawal, but before cows express fertile estrus
Less fertile estrus after
MGA7-10 days
107
2nd estrus for anestrous cows after
short estrous cycle (more
fertile)
2nd estrus for most of cows (more fertile)
Suggested timing of introducing bulls
(see page 104 and 105)
![Page 52: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/52.jpg)
Advantages: Easy to use Shortens the next calving season
(ideal way to start AI program in the following year)
MGA can induce estrous cyclicity in postpartum anestrous cows (Jump-start)
Does not require cattle to be handled
Natural Service with MGA Program
$2.00–$5.60 (MGA cost)
109
![Page 53: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/53.jpg)
Disadvantages: Must have adequate bull-power
At least 1:15 to 20 bull:female ratio for 2-year or older bulls
Yearling bulls … consider decreasing the bull:female ratio
Resulting calves may be of inferior quality and provide less genetic improvement for the herd compared to AI calves (depends on the genetic quality of the clean-up bulls)
Natural Service with MGA Program
$2.00–$5.60 (MGA cost)
110
![Page 54: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/54.jpg)
Summation
• Lots of programs– Many combinations of programs
• Many prices• The numbers definitely show results
– Earlier calving season– More time to return to Estrus– Increased opportunity to become pregnant
• However due to expense and labor intensity this is not for everyone
![Page 55: The Estrous Cycle in Cattle](https://reader034.fdocuments.net/reader034/viewer/2022042707/5867771a1a28abb4408bb910/html5/thumbnails/55.jpg)
Bibliography
• “Guide to Estrus Synchronization
of Beef Cattle” CDFreddie N. Kojima, Ph.D.and David J.
Patterson, Ph.D.Department of Animal Sciences University of Missouri Columbia, MO 65211