David L. Thomas Department of Animal Sciences University of Wisconsin-Madison Basics of Sheep Breeding for Commercial Flocks

Production (P) of a sheep is dependent upon: - The genes of the sheep (genotype, G) - The environment in which the sheep is raised (E), i.e. nutrition, health program, housing, temperature, humidity, parasite challenge, etc. Production = Genotype + Environment P = G + E =+

Production (P) of a sheep is dependent upon: Production = Genotype + Environment P = G + E Genotype = Breeding Value (BV) + Gene Combination Value (GCV) Therefore: Production = Breeding Value + Gene Combination Value + Environment P = BV + GCV + E

BV = breeding value = sum of the independent effects of each allele affecting the trait (+ or – deviation) Individual alleles, and therefore independent allele effects, are passed from parent to offspring, so a sheep’s BV is used to predict the performance of its progeny (i.e. EPD). The proportion of differences between sheep in performance that is due to the differences in their breeding values is heritability (h 2 ) of that trait. h 2 = BV variation / Performance variation

Heritabilities of Sheep Traits TraitHeritability Litter size born.10 Lb. lamb weaned per ewe day (weaning) wt day (postweaning) wt..20 Loin eye area.35 Fat thickness.30 % trimmed retail cuts.40 Fleece wt..35 Fleece length.55 Fleece fiber diameter.40 Milk yield.30 % milk fat.40 % milk protein.40

Visual Traits Characteristics that you can see, such as: Conformation Height Length Wool quality are highly heritable. If such traits are of great economic importance in your flock, select sheep that have the appearance you desire.

Selection for Conformation is Effective However, conformation is not highly correlated with performance for many production traits. U.S. Southdowns – Then and Now – In Changing Conformation

U.S. Shropshires: 1946 – st Place Fall Ram Lamb, 2005 IL State Fair Brockmann Family, IL

Production Traits Traits that result in improved lamb, wool, and/or milk production Litter size, lamb survival, milk production, weaning weight, postweaning gain, loin eye area, fat thickness, fleece weight, disease resistance, etc.

Production Traits 1.Initial selection on performance records – without looking at the animals. Select 10 – 15% more animals than needed. 2.Visual appraisal of only the animals selected on the basis of records. Cull the poorest 10 – 15% on visual appraisal. Steps in the selection of replacement ewes for production traits

Selection of Replacement Ewe Lambs UW Minimum record-keeping requirements: 1.Individual identification of ewes and lambs 2.Record birth date ID, dam, and sex of each lamb 3.Record number of lambs born and raised by each ewe and birth- rearing type of each lamb 4.Weigh lambs at weaning and record date of weaning

Adjust Litter Size for Age of Ewe Adjust litter size for age of the ewe. Select replacement ewe lambs from dams with high average adjusted litter size. Age of Ewe Multiplicative Adjustment Factors for Litter Size Age, yr.Adjustment

Example of Adjusted Litter Size EweAge Actual litter size Adj. litter size Ave. adj. litter size Age of Ewe Multiplicative Adjustment Factors for Litter Size Age, yr.Adjustment Even though both ewes produced 3 lambs in two years, Ewe 722 is expected to be genetically superior, and her ewe lambs should be considered as replacements.

Estimated Breeding Value (EBV) EweAge Actual litter size Adj. litter size Ave. adj. litter size Difference in EBV between 722 and 205 based on their first record: EBV = h 2 (1.48 – 1.00) =.10 (.48) =.048 lambs 722 is estimated to have a genetic superiority of.05 more lambs per litter than 205. Difference in EBV between 722 and 205 based on the average of their two records: EBV = h 2 average of 2 records (1.91 – 1.52) =.17 (.61) =.104 lambs 722 is estimated to have a genetic superiority of.10 more lambs per litter than 205 based on two records.

Selection of Replacement Rams Most commercial flocks purchase their rams Since fewer rams are selected than ewes, rams should have higher genetic values than ewes Most of the genetic improvement in flocks is the result of ram selection rather than ewe selection Select rams from flocks that are serious about genetic improvement for production traits The most accurate estimate of genetic merit is the Expected Progeny Difference (EPD) EPDs are calculated by the National Sheep Improvement Program (NSIP)

Suffolk Genetic Trend and Performance Performance of NSIP Suffolks in 2008 TraitAverage 60-day weaning weight, lb63.2 Postweaning average daily gain, lb/d day postweaning weight, lb116.3 Litter size1.88

Almost all commercial flocks should be utilizing crossbreeding

Crossbreeding – Why? Paternal male x Maternal female Maternal male x Paternal female 1.Breed complementarity – Utilize the strong points of two or more breeds in a crossbreeding system to maximize performance. Good example: Suffolk ram x Polypay ewe Poor example: Polypay ram x Hampshire ewe 2.Hybrid vigor or heterosis – increased performance of crossbreds compared to the purebreds that make up the cross.

Hybrid Vigor Example – 60-day Weaning Weight Suffolk x Suffolk lambs = 60 lb. Polypay x Polypay lambs = 50 lb. Polypay x Suffolk and Suffolk x Polypay lambs = 58 lb. Average of purebred Suffolk and Polypay lambs = ( ) / 2 = 55 lb. Hybrid vigor = 58 – 55 = 3 lb. % HV = ((crossbred – purebred) / purebred) x 100 = ((58 – 55) / 55) x 100 = (3 / 55) x 100 =.05 x 100 = 5 %

% Individual HV for Sheep (purebred rams mated to purebred ewes to produce crossbred lambs) Trait% Ind. HV Ewe fertility 2.6 % Ewe litter size 2.8 % Lamb survival to weaning 9.8 % Lamb birth weight 3.2 % Lamb weaning weight 5.0 % Lamb postweaning gain 6.6 % Lambs reared / ewe exposed 15.2 % Weight of lamb weaned / ewe exposed 17.8 % Fleece weight 5.0 % Carcass traits ~ 0.0 %

Maternal and Paternal Hybrid Vigor Maternal HV - increased performance of an individual due to its dam being crossbred (or from a mating utilizing a crossbred dam) Paternal HV - increased performance of an individual due to its sire being crossbred (or from a mating utilizing a crossbred sire)

Estimates of Hybrid Vigor TraitInd., %Mat., % Conception rate Litter size Lamb survival Lamb weaning wt Lamb wt. wn./ewe mated Post-weaning wt Carcass traits

Estimates of Hybrid Vigor TraitInd., %Mat., %Pat., % Conception rate (30.0 if fall mating) Litter size Lamb survival Lamb weaning wt Lamb wt. wn./ewe mated Post-weaning wt Carcass traits

Cross rams x Cross ewes = 4-breed cross lambs Pure rams x Pure ewes = Pure lambs Trait % Ind. HV % Mat. HV % Pat. HV Lb. lamb weaned / ewe mated 18 % 3 % % Pure rams x Pure ewes = 2-breed cross lambs+ 18 % + 39 % Pure rams x Cross ewes = 3-breed cross lambs Individual HV = 18% Maternal HV = 18% Paternal HV = 3%

Crossbreeding Systems Performance of three breeds of sheep Breed Fertility, % Prolificacy, no. Lamb survival, % Lamb wean. wt., lb. Wt. wean. per ewe, lb. Finnsheep Dorset Hampshire Average

Crossbreeding Systems 100 ewe flock All ewe replacements are produced within the flock All rams are purebred and purchased. No pure Finnsheep ewes are used.

3-Breed Terminal Crossbreeding System Hampshire rams x 55 FinnxDorset ewes Finnsheep rams x 25 Dorset ewes Dorset rams x 20 Dorset ewes Market Lambs Male lambs and a few cull ewe lambs All Hampshire-sired lambs Advantages: Good breed complementarity Disadvantage: Too many purebred ewes – reduced maternal hybrid vigor 87 lb. lamb weaned per ewe exposed

3-Breed Rotational Crossbreeding System Dorset rams x H(FD) ewes Hampshire rams x FxD ewes Finnsheep rams x Dorset ewesMarket Lambs Advantages: All ewes (after start) and all lambs are crossbred – good use of individual and maternal hybrid vigor (86% of maximum) Disadvantage: Poor breed complementarity 85 lb. lamb weaned per ewe exposed Finnsheep rams x D(HFD) ewes Hampshire rams x F(DHF) ewes Male lambs and cull ewe lambs (system continues to rotate sire breed)

3-Breed Roto-Terminal Crossbreeding System F rams x DF ewes D rams x FD ewes F rams x D ewes Market Lambs Advantages: 1) All ewes (after start) and all lambs are crossbred – good use of individual and maternal hybrid vigor (67% of Mat HV, 67% & 100% Ind HV) 2) Good breed complementarity Disadvantage: ? 95 lb. lamb weaned per ewe exposed D rams x FD ewes Hamp-sired lambs, F- and D- sired male lambs, some F- and D- sired ewe lambs Rotation (25-35 ewes) Terminal (65-75 ewes) FD ewes x Hamp rams DF ewes x Hamp rams FD ewes x Hamp rams (system continues)

Final Comments on Crossbreeding 1.Good crossbreds result from good purebreds. 2.Don’t expect hybrid vigor to compensate for poor or inappropriate genetics. 3.Limit the number of breeds to those that have high levels of performance. 4.Hybrid vigor is maximized when no breeds are in common in the sire and dam. 5.More hybrid vigor is obtained when less related breeds are crossed. 6.An organized crossbreeding system is needed to take best advantage of hybrid vigor and breed complementarity.

Performance Years breed selection – without genetic improvement over time in the purebreds breed selection + selection in the purebreds + crossbreeding breed selection + selection in the purebreds Where the commercial sheep industry should be!! Where the purebred sheep industry should be!! Effective Utilization of Genetics in the U.S. Sheep Industry

Adjustment of Lamb Weaning Weight for Age at Weighing LambBirth wt., lb. Weaning age, days Actual wn. wt., lb. 60-day weaning wt d WW = (((actual WW – actual BW) / actual wean age, days) x 60) + actual BW

Adjustment of Lamb Weaning Weight for Age of Dam, Sex of Lamb, and Type of Birth-Rearing of Lamb Multiplicative Adjustments for Lamb Weaning Weight ItemClassAdj. Factor Age of dam, yr Sex of lamb Ram.91 Wether.97 Ewe1.00 Type of birth-rearing of lamb Single - Single 1.00 Single - Twin 1.17 Twin - Single 1.11 Twin - Twin 1.21 Triplet+ - Single 1.19 Triplet+ - Twin 1.29 Triplet+ - Triplet+ 1.36

Final Adjustment of Lamb Weaning Weight for Age at Weighing, Age of Dam, Sex of Lamb, and Type of Birth-Rearing of Lamb Lamb 60-day WW, lb. (Age of dam, yr.) Adj. (Sex) Adj. (Type B-R) Adj. Final 60-d adj. WW, lb (3) x 1.00 (Ewe) (Tw – Tw) x (8) x 1.05 (Ewe) x 1.00 (Tr – Tw) x Adj. 60-d WW = 60-d WW x Age of Dam Adj. x Sex of Lamb Adj. x Type of Birth-Rearing of Lamb Adj. Lamb 9038 is estimated to be genetically superior over lamb 9005 for weaning weight and should be selected.

Maximize HV HV is maximized when there are no breeds in common between the sire and dam. Hampshire ram x Polypay ewe = Hamp x Polypay cross lambs = ½ H, ½ P lambs (100% maximum HV I ) (Polypay x Hampshire) ram x (Polypay x Suffolk) ewe = (P x H) x (P x S) lambs = ½ P, ¼ H, ¼ S lambs (75% maximum HV I ) Hampshire ram x (Hampshire x Polypay) ewe = H x (H x P) lambs = ¾ H, ¼ P lambs (50% maximum HV I ) Hampshire ram x Hampshire ewe = Hampshire lambs (no HV I )

Comparison of Sheep Crossbreeding Systems (lb. of lamb weaned per ewe exposed) System No. lambs weaned Lb. lamb weaned Advantage over purebreeding in lb. lamb weaned Purebreeding, A x A47623, breed terminal, C x A53629,08022 % 2-breed rotation, A-B59231,78034 % 3-breed terminal, C x (A x B)62035,60850 % 3-breed roto-terminal, C x A-B61234,72846 % 400 ewes in each flock, all replacement females produced in the flock, number of lambs weaned and pounds of lamb weaned do not include the ewe lambs kept for replacements.