Breeding better sheep

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.

1. Breeding “better” sheep SUSAN SCHOENIAN Sheep & Goat Specialist Western Maryland Research & Education Center University of Maryland Extension [email protected] – www.sheepandgoat.com

2. Today’s topics Defining “better” Better for what? Nature vs. nurture Genetics vs. environment Ways to genetically improve sheep Crossbreeding Selection

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 Industry American 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. nurture Heredity (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 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

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. Greatest for reproductive and fitness traits.

16. 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. Strengths of sire breed offset weaknesses of dam breed and vice versa. Suffolk x Katahdin Finn x Dorset Suffolk x Texel

19. 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.

20. Crossbreeding systems Terminal All offspring are marketed. Katahdin ewe x Suffolk ram = market lambs Rotational Dual-purpose rams are alternated Dorset x Columbia = ewes + market lambs Roto -terminal Rotational (to produce ewe replacements); terminal to produce market lambs. 1) Dorset x Ramboullet = ewes 2) 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 ewes Composite x Texel ram = market lambs

21. 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)

22. 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.

23. 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

24. 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.

25. Traits with low heritability, < 20% Trait Heritability Ewe fertility 5 Lamb survival 5 Scrotal hernia (swine) 7 to 1 5 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

26. 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 12 th 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

27. 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

28. 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

29. 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

30. Tools for genetic improvement On-farm performance testing Carcass contests Central performance tests Across-flock genetic comparisons (EPDs)

31. 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

32. Contemporary groups Same breed or breed type Same environment Same management group Same feeding program Same season

33. 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

34. 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

35. Thank you for your attention. Do you have any questions?