Breeding better sheep
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Transcript of Breeding better sheep
BREEDING “BETTER” SHEEP
SUSAN SCHOENIANSheep & Goat Specialist
Western Maryland Research & Education CenterUniversity of Maryland Extension
[email protected] – www.sheepandgoat.com
TODA
Y’S
TOPI
CS
• Defining “better”– Better for what?
• Nature vs. nurture– Genetics vs. environment
• Ways to genetically improve sheep– Crossbreeding– Selection
WHAT IS “BETTER”? (according to Google™)
• Something superior in quality, condition, or effect.
• From a position of superiority or authority.
• The superior one of two alternatives.
• Superior to another (of the same class or kind) in excellence, quality, desirability, or suitability.
THE U.S. SHEEP INDUSTRYAmerican Sheep Industry Association Survey, April 2010
6422
104
0.4
.
Commercial Seedstock Club lamb Lamb feeder Dairy
WHY DO YOU RAISE SHEEP?
• Commercial – Meat– Wool
• Seedstock (show)
• Club lambs
• Dairy production
COMMERCIAL MEAT PRODUCTION
Important
• Performance– Reproductive efficiency
• LBS. QUALITY LAMB WEANED
– Growth and carcass (sire)• Post-weaning ADG• Market suitability
• Fitness– Disease-resistant– Longevity– Easy-care
Less important (ewes)• Body conformation• Wool
WOOL PRODUCTION
Important
• Wool – Quality – Quantity
• Color• Character
Less important• Body conformation• Reproductive efficiency• Fitness
SEEDSTOCK (SHOW ANIMALS)
Important• Body conformation
– Frame size– Structural correctness– Muscling
• Whatever the current “fad” for your breed is.
Less important• Reproductive efficiency• Fitness• Wool production
CLUB LAMBS
Important• Type• Body conformation• Eye appeal (“X” factor)
Less important
• Reproductive efficiency• Fitness• Wool
DAIRYImportant• Milk production
– Quantity– Quality
• Udder conformation• Disposition
Less important
• Body conformation• Wool• Fitness
NATURE VS. NURTUREHeredity (genetics) vs. environment
GENOTYPE• The genetic make-up of an
individual.• The genes or alleles present
in an individual.• An individual’s genetic
information.
PHENOTYPE• Physical appearance of an
individual.• Observable or measurable
traits.• Genetics + environment
ENVIRONMENTAL FACTORS AFFECTING PHENOTYPE
• Nutrition• Health• Weather• Season• Management• Housing• Pasture management• Age
Genetics is permanent. The environment changes.
NATURE VS. NURTURE
Genotype• On-farm
– Adjusted weaning weights– Adjusted litter weights– Flock EPDs (expected progeny
difference).
• Across-flock– EPDs or EBVs– Differences in performance at Central
Ram Test Stations
• Individual genes– Fecundity gene– Myostatin gene– Scrapie-resistance
Phenotype
• What an animal looks like– Visual appraisal
• How an animal performs– Actual performance levels
THERE ARE TWO WAYS TO GENETICALLY “IMPROVE” SHEEP.
1) CROSSBREEDING• Mating individuals of
different breeds or types.
2) SELECTION
• Natural– “Survival of the fittest”
→ Artificial– Human intervention– Choosing which individuals
get to become parents.
CROSSBREEDING HAS TWO DISTINCT ADVANTAGES
1. Hybrid vigor (heterosis)
• Improved performance of offspring compared to the average of their parents.
1. Individual2. Maternal3. Paternal
• Effects are additive.
• Greatest for reproductive and fitness traits.
HETEROSIS IN THE CROSSBRED LAMB
HETEROSIS IN THE CROSSBRED EWE
CROSSBREEDING HAS TWO DISTINCT ADVANTAGES
2. Complementarity
• Improvement in performance of crossbred offspring resulting from the crossing of breeds of different, but complementary biological types.
• Strengths of sire breed offset weaknesses of dam breed and vice versa.
1. Suffolk x Katahdin2. Finn x Dorset3. Suffolk x Texel
SHEEP CROSSBREEDING PROGRAMS
• Should be a planned program to produce desired types of animals or fleeces.
• Should optimize performance of flock.
• Should use breeds in appropriate roles.
Does not imply indiscriminate mixing of breeds or types.
CROSSBREEDING SYSTEMS1. Terminal
• All offspring are marketed.Katahdin ewe x Suffolk ram = market lambs
2. Rotational• Dual-purpose rams are alternated
Dorset x Columbia = ewes + market lambs
3. Roto-terminal• Rotational (to produce ewe replacements);
terminal to produce market lambs.1) Dorset x Ramboullet = ewes2) D x R ewes x Suffolk ram = market lambs
4. Composite-terminal• New breed is formed (composite) and mated to
terminal ram for market lamb production.Polypay x Polypay = composite ewesComposite x Texel ram = market lambs
SELECTION• Select for one trait
– Can lead to problems
• Select for multiple traits– Progress will be slower for individual
traits, but it results in more balanced selection (and sheep).
• Minimum standards1. Weaning wt ratio above 100%2. Twin or better3. Dewormed once as lamb
• Selection index– Lbs. of lamb weaned– Lbs. lamb + 3x lbs. wool
• Pedigree (family selection)
QUALITATIVE VS. QUANTITATIVE TRAITS
Qualitative• Controlled by few genes• Categorical scale• Distinct traits
Quantitative• Influenced by genetics and
environment• Controlled by many genes• Continuous traits• Most traits of economic
importance.
SELECTION: HERITABILITY
• Phenotypic variation due to genetic differences.
• Relationship between phenotype and genotype.
• Percent of phenotypic variation that is transferred to the next generation.
• Degree to which offspring resemble parents
Sire and offspring
SELECTION: HERITABLITY• Individual ewes and rams pass on traits to their offspring based on the heritability of those traits.
• Traits which respond well to crossbreeding (hybrid vigor) do not respond as well to selection and vice versa.
• Heritability is higher for wool traits, growth, and carcass traits, and lower for reproductive and fitness traits.
• Faster progress can be made for traits with high heritability, though lowly heritable traits should not be ignored, as they still have a genetic component.
TRAITS WITH LOW HERITABILITY, < 20%
Trait Heritability
Ewe fertility 5
Lamb survival 5
Scrotal hernia (swine) 7 to 15
Prolificacy 10
60-day weight 10
Dressing percent 10
Parasite resilience 10 to 20
Hock set (rear legs) 12
Foot / pastern angle 13
Rectal prolapse 14
Birth weight 15
90-day weight 15
Pre-weaning gain (0 to 60 days) 15
Entropion (inverted eyelid) 15
Udder depth 16
Udder attachment 17
Teat size 18
TRAITS WITH MODERATE HERITABILITY, 20-40%
Trait Heritability
120-day weight 20
Ewe productivity (lbs. weaned) 20
Teat placement 24
Udder shape 24
Age at puberty 25
Clean fleece weight 25
Milk yield 30
Milk fat percentage 30
Milk protein percentage 30
12th rib fat thickness 30
Femininity 32
Scrotal circumference 35
Grease fleece weight 35
Milk fat yield 35
Loin eye area 35
Mothering ability 39
Body length (beef) 39
TRAITS WITH HIGH HERITABILITY, > 40 %
Trait Heritability
Parasite resistance (fecal egg counts) 20 to 50
Mature body weight 40
Yield (wool) 40
Percent trimmed retail cuts 40
Fiber diameter 40
Muscling 42
Capacity 44
Gestation length 45
Weight of trimmed retail cuts 45
Crimp 45
Color 45
Milk protein yield 45
Staple length 55
Face cover 56
Tail length 39 to 82
WHAT ELSE DETERMINES GENETIC PROGRESS?
• Selection differential – Superiority of selected animals
• Large population• Few animals selected Genetic improvement is made primarily
through the sire
• General interval – Average age of parents when offspring
are born.• Short generation interval Replacements females have the “best”
genetics in the flock.
• Accuracy– Correlation between estimated and
true genetic merit of animal.• High heritability Many records or progeny
EVALUATION METHODS
Visual appraisal (subjective)• Body conformation• Udder conformation• Visual evaluation of wool• Live evaluation/handling• Show winnings
Performance (objective)• Birth records• Growth records• Fleece weights• Milk yields• Micron testing• Ultrasound• Actual carcass measurements
TOOLS FOR GENETIC IMPROVEMENT
• On-farm performance testing• Carcass contests• Central performance tests• Across-flock genetic comparisons (EPDs)
ON-FARM PERFORMANCE TESTING
• Weaning weights– Age– Sex– Type of birth and rearing– Age of dam.
• Post-weaning ADG
• Parasite resistance (fecal egg counts)
• Parasite resistance (FAMACHA© scores and Tx)
• Carcass characteristics
• Fleece characteristics
CONTEMPORARY GROUPS
• Same breed or breed type
• Same environment
• Same management group
• Same feeding program
• Same season
CENTRAL RAM PERFORMANCE TESTS
• Mostly for terminal sire and dual-purpose breeds.
– Virginia– West Virginia– Pennsylvania– Midwest– West
• Growth and feed efficiency• Ultrasound carcass• Fleece characteristics• Type scores• Scrapie and spider genotype
• EPDs Expected Progeny Differences
• National Sheep Improvement Association (NSIP) - www.nsip.org
– Submit data through breed associations
– Breed association determines which traits are important
– Not all breeds participate (minor breeds)
ACROSS-BREED PERFORMANCE EVALUATION
Thank you for your attention.
Do you have any questions?