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.

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Breeding better sheep

  1. 1. Breeding “better” sheep<br />SUSAN SCHOENIANSheep & Goat SpecialistWestern Maryland Research & Education CenterUniversity of Maryland –<br />
  2. 2. Defining “better”<br />Better for what?<br />Nature vs. nurture<br />Genetics vs. environment<br />Ways to genetically improve sheep<br />Crossbreeding<br />Selection <br />Today’s topics<br />
  3. 3. What is “better”?(according to Google™)<br />Something superior in quality, condition, or effect.<br />From a position of superiority or authority.<br />The superior one of two alternatives.<br />Superior to another (of the same class or kind) in excellence, quality, desirability, or suitability.<br />
  4. 4. The U.S. Sheep IndustryAmerican Sheep Industry Association Survey, April 2010<br />
  5. 5. Why do you raise sheep?<br />Commercial <br />Meat<br />Wool<br />Seedstock (show)<br />Club lambs<br />Dairy production<br />
  6. 6. Commercial meat production<br />Important<br />Performance<br />Reproductive efficiency<br />LBS. QUALITY LAMB WEANED<br />Growth and carcass (sire)<br />Post-weaning ADG<br />Market suitability<br />Fitness<br />Disease-resistant<br />Longevity<br />Easy-care<br />Less important (ewes)<br />Body conformation<br />Wool<br />
  7. 7. wool production<br />Important<br />Wool <br />Quality <br />Quantity <br />Color<br />Character<br />Less important<br />Body conformation<br />Reproductive efficiency<br />Fitness<br />
  8. 8. Seedstock (show animals)<br />Important<br />Body conformation<br />Frame size<br />Structural correctness<br />Muscling<br />Whatever the current “fad” for your breed is.<br />Less important<br />Reproductive efficiency<br />Fitness<br />Wool production<br />
  9. 9. Club lambs<br />Important<br />Type<br />Body conformation<br />Eye appeal (“X” factor)<br />Less important<br />Reproductive efficiency<br />Fitness<br />Wool<br />
  10. 10. Dairy<br />Important<br />Milk production<br />Quantity<br />Quality<br />Udder conformation<br />Disposition<br />Less important<br />Body conformation<br />Wool<br />Fitness<br />
  11. 11. Nature vs. nurtureHeredity (genetics) vs. environment<br />GENOTYPE<br />The genetic make-up of an individual.<br />The genes or alleles present in an individual.<br />An individual’s genetic information.<br />PHENOTYPE<br />Physical appearance of an individual.<br />Observable or measurable traits.<br />Genetics + environment<br />
  12. 12. Environmental factors affecting phenotype<br />Nutrition<br />Health<br />Weather<br />Season<br />Management<br />Housing<br />Pasture management<br />Age<br />Genetics is permanent. The environment changes.<br />
  13. 13. Nature vs. nurture<br />Phenotype<br />Genotype<br />What an animal looks like<br />Visual appraisal<br />How an animal performs<br />Actual performance levels<br />On-farm <br />Adjusted weaning weights<br />Adjusted litter weights<br />Flock EPDs (expected progeny difference).<br />Across-flock<br />EPDs or EBVs<br />Differences in performance at Central Ram Test Stations<br />Individual genes<br />Fecundity gene<br />Myostatin gene<br />Scrapie-resistance<br />
  14. 14. There are two ways to genetically “improve” sheep.<br />1) CROSSBREEDING<br />Mating individuals of different breeds or types.<br />2) SELECTION<br />Natural<br />“Survival of the fittest”<br /><ul><li>Artificial</li></ul>Human intervention<br />Choosing which individuals get to become parents.<br />
  15. 15. Crossbreeding has two distinct advantages<br />Hybrid vigor (heterosis)<br /><ul><li>Improved performance of offspring compared to the average of their parents.</li></ul>Individual<br />Maternal<br />Paternal<br /><ul><li>Effects are additive.
  16. 16. Greatest for reproductive and fitness traits.</li></li></ul><li>Heterosis in the crossbred lamb<br />
  17. 17. Heterosis in the crossbred ewe<br />
  18. 18. Crossbreeding has two distinct advantages<br />Complementarity<br /><ul><li>Improvement in performance of crossbred offspring resulting from the crossing of breeds of different, but complementary biological types.
  19. 19. Strengths of sire breed offset weaknesses of dam breed and vice versa.</li></ul>Suffolk x Katahdin<br />Finn x Dorset<br />Suffolk x Texel<br />
  20. 20. Sheep Crossbreeding programs<br />Should be a planned program to produce desired types of animals or fleeces.<br />Should optimize performance of flock.<br />Should use breeds in appropriate roles.<br /><ul><li>Does not imply indiscriminate mixing of breeds or types.</li></li></ul><li>Crossbreeding systems<br />Terminal<br /><ul><li>All offspring are marketed.Katahdin ewe x Suffolk ram = market lambs</li></ul>Rotational<br /><ul><li>Dual-purpose rams are alternatedDorset x Columbia = ewes + market lambs</li></ul>Roto-terminal<br /><ul><li>Rotational (to produce ewe replacements); terminal to produce market lambs.1) Dorset x Ramboullet = ewes2) D x R ewes x Suffolk ram = market lambs</li></ul>Composite-terminal<br /><ul><li>New breed is formed (composite) and mated to terminal ram for market lamb production.Polypay x Polypay = composite ewesComposite x Texel ram = market lambs</li></li></ul><li>Selection<br />Select for one trait<br />Can lead to problems<br />Select for multiple traits<br />Progress will be slower for individual traits, but it results in more balanced selection (and sheep). <br />Minimum standards<br />Weaning wt ratio above 100%<br />Twin or better<br />Dewormed once as lamb<br />Selection index<br />Lbs. of lamb weaned<br />Lbs. lamb + 3x lbs. wool<br />Pedigree (family selection)<br />
  21. 21. Qualitative vs. quantitative traits<br />Qualitative<br />Controlled by few genes<br />Categorical scale<br />Distinct traits<br />Quantitative<br />Influenced by genetics and environment<br />Controlled by many genes<br />Continuous traits<br />Most traits of economic importance.<br />
  22. 22. Selection: Heritability<br />Phenotypic variation due to genetic differences.<br />Relationship between phenotype and genotype.<br />Percent of phenotypic variation that is transferred to the next generation.<br />Degree to which offspring resemble parents<br />Sire and offspring<br />
  23. 23. Selection: heritablity<br />Individual ewes and rams pass on traits to their offspring based on the heritability of those traits.<br />Traits which respond well to crossbreeding (hybrid vigor) do not respond as well to selection and vice versa.<br />Heritability is higher for wool traits, growth, and carcass traits, and lower for reproductive and fitness traits.<br />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.<br />
  24. 24. Traits with low heritability, < 20%<br />
  25. 25. Traits with moderate heritability, 20-40%<br />
  26. 26. Traits with high heritability, > 40 %<br />
  27. 27. What else determines genetic progress?<br />Selection differential <br />Superiority of selected animals<br />Large population <br />Few animals selected<br /><ul><li>Genetic improvement is made primarily through the sire</li></ul>General interval <br />Average age of parents when offspring are born.<br />Short generation interval<br /><ul><li>Replacements females have the “best” genetics in the flock.</li></ul>Accuracy<br />Correlation between estimated and true genetic merit of animal.<br />High heritability<br /><ul><li>Many records or progeny </li></li></ul><li>Evaluation methods<br />Visual appraisal (subjective)<br />Body conformation<br />Udder conformation<br />Visual evaluation of wool<br />Live evaluation/handling<br />Show winnings<br />Performance (objective)<br />Birth records<br />Growth records<br />Fleece weights<br />Milk yields<br />Micron testing<br />Ultrasound<br />Actual carcass measurements<br />
  28. 28. Tools for genetic improvement<br />On-farm performance testing<br />Carcass contests<br />Central performance tests<br />Across-flock genetic comparisons (EPDs)<br />
  29. 29. On-farm performance testing<br />Weaning weights<br />Age<br />Sex<br />Type of birth and rearing<br />Age of dam.<br />Post-weaning ADG<br />Parasite resistance (fecal egg counts)<br />Parasite resistance (FAMACHA© scores and Tx)<br />Carcass characteristics<br />Fleece characteristics<br />
  30. 30. Contemporary groups<br />Same breed or breed type<br />Same environment<br />Same management group<br />Same feeding program<br />Same season<br />
  31. 31. Central ram performance tests<br />Mostly for terminal sire and dual-purpose breeds.<br />Virginia<br />West Virginia<br />Pennsylvania<br />Midwest<br />West<br />Growth and feed efficiency<br />Ultrasound carcass<br />Fleece characteristics<br />Type scores<br />Scrapie and spider genotype<br />
  32. 32. EPDs Expected Progeny Differences<br />National Sheep Improvement Association (NSIP) -<br />Submit data through breed associations<br />Breed association determines which traits are important<br />Not all breeds participate (minor breeds)<br />Across-breed performance evaluation<br />
  33. 33. Thank you for your attention.Do you have any questions?<br />