Genetic Selection of HorsesIntroductionWhat traits do horse breeders select for?Difficult to Measure TraitsGENETIC RELATIONSHIP TO OFFSPRINGBreeding SystemsSlide 7OutbreedingSlide 9Slide 10Effect of inbreedingPerformance Trait SelectionPerformance TestingProgeny testingSib or family selectionLimitations of stallion indexesHeritability EstimateHeritability EstimateSelection processTwo basic types of genetic actionTwo basic types of genetic actionType of QualitativeTypes of QualitativeHorse GTG IdiogramParentage TestingSlide 26Qualitative exampleSlide 28Qualitative example Color related allele - partial dominanceQualitative example “LETHAL WHITE IN OVERO PAINT HORSES”Quantitative exampleWHAT’S NEW?Glycogen Branching Enzyme Deficiency (GBED)Slide 34Polysaccharide Storage Myopathy (PSSM)PSSMExertional RhabdomyolysisHyperelastosis Cutis (HC/HERDA)Genetic Selection of HorsesIntroduction•Genetics are not as utilized in the horse industry as in livestock species who select for size, length, weight, efficiency of or maximal production of livestock •Horse breeders look more at pedigree, eye catching traits, and subjective criteriaWhat traits do horse breeders select for? •Soundness•Conformation•Reproduction•Athletic ability–Speed –Style (Hunter etc.)•Color pattern•Disposition/manners•PerformanceDifficult to Measure Traits •Conformation•Disposition•Athletic ability•IntelligenceGENETIC RELATIONSHIP TO OFFSPRINGRELATIONSHIP % RELATIONSHIPDIRECT Sire or Dam 50.0 Grand sire or dam 25.0 Great grand sire or dam 12.5COLLATERAL Full-sib 50.0 3/4 Brother or sister 37.5 Half-sib 25.0 First cousin 12.5Breeding Systems•Crossbreeding - breeding different breeds together–major heterosis - variable results–breed registry book:•closed - AHR and Half-Arabian•open - ApHC and APHA to QH–AQHA, ApHC, APHA to TBBreeding Systems•Outbreeding - mating crosses of horses less related than the average within a breed–variability large–heterozygosity increases–increases genetic “pool”Native DancerRaise A NativeLines of PowerRaise YouBold RulerExotic Garden POLITICAL WHITThe Garden ClubMatsadoonDoonesbury Political ParodyVaguely NiceRobertoUrakawa Miss DevereuxOutbreedingBreeding Systems•Inbreeding - –breeding horses more related than the breed average•increases homozygosity•increases the predominance of recessive diseases•uniformity of offspring increases•Linebreeding - increases the relationship to some admired ancestor–relationships within a pedigree are additiveThree BarsZippo Pat BarsLeo PatI InspireBig Step Teeny StepTeeny BrownCK Zippos Bar BeeZippo Pat Bars Zippo Bar PineDollie PineZip Bar BeeDouble Bar Leo Money Bee HoneyChetterette BarEffect of inbreeding•Uncover undesirable recessive genes•Reduced vigor•Reduction in growth rate•Increased mortality in offspring•Reduced immune response of foalsPerformance Trait Selection•How do we measure performance traits–# of wins/placings in shows–dollars earned–points earned/horses beaten–race placings - speedPerformance Testing •100 day test in warmbloods at stallion testing center•Train and compete horses before breedingProgeny testing •Train and compete offspring•Only breed those animals with superior performance offspringSib or family selection •Relies on performance of collateral relatives•Performance data in the pedigree•Often seen in sales catalog pages and reference stallions•Look for black type1st damBRAVE RAJ, by Rajab. 6 wins in 9 starts at 2, $933,650, champion 2-year-old filly in U.S., Breeders' Cup Juvenile Fillies S. [G1], Del Mar Debutante S. [G2], Sorrento S. [G3], Florida Stallion/My Dear Girl S. [LR] (CRC, $240,000), Florida Stallion/Susan's Girl S. [LR] (CRC, $45,000), 2nd Junior Miss S. [L] (DMR, $10,000). Dam of 14 foals, 11 to race, 10 winners-- BRAVO BULL (c. by Holy Bull). Black type winner, see below. RUSSIAN TANGO (f. by Nijinsky II). 4 wins at 3 and 4, $92,390, The Very One H. [L] (GP, $30,000). Dam of-- EUROSILVER (c. by Unbridled's Song). 4 wins, 2 to 4, 2005, $622,310, Lane's End Breeders' Futurity [G2] (KEE, $248,000), Skip Away H. [G3] (GP, $60,000), 2nd Stephen Foster H. [G1] (CD, $165,600), Swale S. [G3] (GP, $30,000), Perryville S. [L] (KEE, $22,520).Limitations of stallion indexes•Average of all offspring is unknown–only superior animals compete•Mare contributions hard to quantify–stallion managers screen superiority•Points, $$’s, and purse size influences •Miles and resources give advantage–Honor roll vs world championHeritability Estimate •Definition –Percentage of a horse's expressed trait (phenotype) that is due to genetics–Due to genetics indicates the probability of trait being passed on from one generation to the next–Specifically, ability to select horses to mate based on superior performance for the trait and to predict the improvement in the offspringTrait Due to Genetics (%)Due to Environment (%)Height at withers 45-50 50-55Body weight 25-30 70-75Body length 35-40 60-65Pulling Power 20-30 70-80Running speed 35-40 60-65Walking speed 40-45 55-60Trotting speed 35-45 55-65Temperament 25-30 70-75Heritability EstimateSelection process •Greater progress when keeping # of selected traits to a minimum•Low heritabilty est. traits: increase success by controlling environment and management regimesTwo basic types of genetic action •Qualitative –Particular trait is influenced by a single pair of genes (or maybe 2 or 3 pairs)Two basic types of genetic action •Quantitative –Trait that is influenced by numerous different genes–Effects of many genes are added together to produce trait –Each gene only has small effect of trait–Most traits are quantitativeType of Qualitative •Dominance: ability of gene to mask or cover up its recessive allele –Only one dominant gene is required to display a particular trait–Two recessive genes are required for a recessive trait to be exhibitedTypes of Qualitative•Co-dominance –Gene action results in an intermediate state between two parents example: blood type–Each blood type is different, known, and indicates genotypeHorse GTG Idiogram•E. caballus–64 chromosomes•E. assinus–62 chromosomes•Odd hybrids are sterile–Mule–Hinny –zorseParentage Testing•Blood type group - AB on RBC surface–electrophoresis of 8 proteins - very specific –used to detect NI (neonatal isoerthyyhtolysis) - like Rh factor in humans