BREEDING “BETTER” SHEEP

SUSAN SCHOENIANSheep & Goat Specialist

Western Maryland Research & Education CenterUniversity of Maryland Extension

sschoen@umd.edu – www.sheepandgoat.com

TODA

Y’S

TOPI

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• 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

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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?