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”
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.
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
Dual-purpose rams are alternatedDorset x Columbia = ewes + market lambs
Rotational (to produce ewe replacements); terminal to produce market lambs.1) Dorset x Ramboullet = ewes2) D x R ewes x Suffolk ram = market lambs
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.
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)
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?