nineteenhorse - GENETICS OF HORSES ANS 3384 WHY ARENT...

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Unformatted text preview: GENETICS OF HORSES ANS 3384 WHY ARENT HORSES GETTING FASTER? Human sprinters are periodically breaking their world record times at a number of distances Genetic improvement is clearly occurring in all food animal species Record times for the triple crown and other important races have not been broken for many years (Secretariat was a long time ago) Genetic Progress per Year Accuracy of Selection Intensity of Selection Genetic Variability Generation Interval Genetic Variability If no genetic variability remains in the population, no response to selection will occur A lack of genetic variability would be shown in very low levels of heritability It could be caused by high levels of inbreeding Inbreeding is avoided today, BUT .. Founding Thoroughbred Sires Founding Sire % of Genes Today GODOLPHIN ARABIAN 14.6% DARLEY ARABIAN 7.5% CURWEN BAY BARB 5.6% BYERLY TURK 4.8% The top 10 ancestors contribute over 50% of the genes in todays population of Thoroughbreds and there were only about 80 foundation animals. Two sons of the Godolphin Arabian born in England Pedigree of GULCH, which shows no inbreeding Pedigree of A. P. INDY, with several common ancestors Also, fertility is quite low in Thoroughbreds Only 40 to 50% of matings result in a live foal But, after 13 years of age, fertility of mares does decline And, breeding is likely occurring too early in the season as horses are long- day breeders But, heritability seems not to be the problem h 2 for speed ranges from .20 to as high as .50 h 2 for conformation traits ranges from .20 to .40 and wither height is higher yet at over .50 But h 2 for reproductive traits is very low What about intensity of selection? In England, about the top 50% of the mares are used for breeding And only the top 6% of the stallions are used as sires Thus, it would seem that there is sufficient intensity of selection Effect of No AI in Thoroughbreds Greater numbers of males must be utilized as sires This reduces intensity of selection But it also could reduce potential inbreeding It may reduce the possibility of rapidly spreading a genetic defect Improvements in reproductive management have led to over 100 mares being served per season What about Accuracy of Selection?...
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This note was uploaded on 07/16/2011 for the course ANS 3384 taught by Professor Olson during the Spring '09 term at University of Florida.

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nineteenhorse - GENETICS OF HORSES ANS 3384 WHY ARENT...

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