Breeding better sheep
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This PowerPoint is from a seminar originally presented at the 2010 Maryland Sheep & Wool Festival by Susan Schoenian, Sheep & Goat Specialist for University of Maryland Extension.

This PowerPoint is from a seminar originally presented at the 2010 Maryland Sheep & Wool Festival by Susan Schoenian, Sheep & Goat Specialist for University of Maryland Extension.

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    Breeding better sheep Breeding better sheep Presentation Transcript

    • Breeding “better” sheep
      SUSAN SCHOENIANSheep & Goat SpecialistWestern Maryland Research & Education CenterUniversity of Maryland Extensionsschoen@umd.edu – www.sheepandgoat.com
    • Defining “better”
      Better for what?
      Nature vs. nurture
      Genetics vs. environment
      Ways to genetically improve sheep
      Crossbreeding
      Selection
      Today’s topics
    • 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
    • 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
    • Dairy
      Important
      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
      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
    • 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
      Hybrid vigor (heterosis)
      • Improved performance of offspring compared to the average of their parents.
      Individual
      Maternal
      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
      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.
      Suffolk x Katahdin
      Finn x Dorset
      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 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)
    • 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%
    • Traits with moderate heritability, 20-40%
    • Traits with high heritability, > 40 %
    • 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?