Breeding better sheep
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  • 1. Breeding “better” sheep
    SUSAN SCHOENIANSheep & Goat SpecialistWestern Maryland Research & Education CenterUniversity of Maryland Extensionsschoen@umd.edu – www.sheepandgoat.com
  • 2. Defining “better”
    Better for what?
    Nature vs. nurture
    Genetics vs. environment
    Ways to genetically improve sheep
    Crossbreeding
    Selection
    Today’s topics
  • 3. 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.
  • 4. The U.S. Sheep IndustryAmerican Sheep Industry Association Survey, April 2010
  • 5. Why do you raise sheep?
    Commercial
    Meat
    Wool
    Seedstock (show)
    Club lambs
    Dairy production
  • 6. 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
  • 7. wool production
    Important
    Wool
    Quality
    Quantity
    Color
    Character
    Less important
    Body conformation
    Reproductive efficiency
    Fitness
  • 8. 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
  • 9. Club lambs
    Important
    Type
    Body conformation
    Eye appeal (“X” factor)
    Less important
    Reproductive efficiency
    Fitness
    Wool
  • 10. Dairy
    Important
    Milk production
    Quantity
    Quality
    Udder conformation
    Disposition
    Less important
    Body conformation
    Wool
    Fitness
  • 11. 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
  • 12. Environmental factors affecting phenotype
    Nutrition
    Health
    Weather
    Season
    Management
    Housing
    Pasture management
    Age
    Genetics is permanent. The environment changes.
  • 13. Nature vs. nurture
    Phenotype
    Genotype
    What an animal looks like
    Visual appraisal
    How an animal performs
    Actual performance levels
    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
  • 14. 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.
  • 15. Crossbreeding has two distinct advantages
    Hybrid vigor (heterosis)
    • Improved performance of offspring compared to the average of their parents.
    Individual
    Maternal
    Paternal
    • Effects are additive.
    • 16. Greatest for reproductive and fitness traits.
  • Heterosis in the crossbred lamb
  • 17. Heterosis in the crossbred ewe
  • 18. Crossbreeding has two distinct advantages
    Complementarity
    • Improvement in performance of crossbred offspring resulting from the crossing of breeds of different, but complementary biological types.
    • 19. Strengths of sire breed offset weaknesses of dam breed and vice versa.
    Suffolk x Katahdin
    Finn x Dorset
    Suffolk x Texel
  • 20. 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 systems
    Terminal
    • All offspring are marketed.Katahdin ewe x Suffolk ram = market lambs
    Rotational
    • Dual-purpose rams are alternatedDorset x Columbia = ewes + market lambs
    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
    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 standards
    Weaning wt ratio above 100%
    Twin or better
    Dewormed once as lamb
    Selection index
    Lbs. of lamb weaned
    Lbs. lamb + 3x lbs. wool
    Pedigree (family selection)
  • 21. 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.
  • 22. 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
  • 23. 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.
  • 24. Traits with low heritability, < 20%
  • 25. Traits with moderate heritability, 20-40%
  • 26. Traits with high heritability, > 40 %
  • 27. 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
  • 28. Tools for genetic improvement
    On-farm performance testing
    Carcass contests
    Central performance tests
    Across-flock genetic comparisons (EPDs)
  • 29. 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
  • 30. Contemporary groups
    Same breed or breed type
    Same environment
    Same management group
    Same feeding program
    Same season
  • 31. 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
  • 32. 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
  • 33. Thank you for your attention.Do you have any questions?