Predicting performance potential in young horses The racing success of a Thoroughbred horse is determined by a multitude of factors, many of which are impossible to evaluate. Thoroughbreds destined for the racetrack are often sold at weanling or yearling sales where buyers must rely on subjective methods, rather than performance history, to select future athletes. Despite careful analysis of pedigree and conformation by breeders, trainers, bloodstock agents, and owners, there have been no fail-proof methods for predicting potential success of young horses. The genetic make-up, or genotype, contributes to a horse's racing ability by influencing conformation, ultimate size, speed potential, and mental attributes including the "will to win." Environmental factors such as nutrition, exercise and conditioning are difficult to quantify, management during growth and development, as well as trainer variation, all influence the horse's potential for success.
The genetic makeup, or genotype, contributes to a horse's performance ability by determining ultimate size and influencing conformation and athletic potential. Growth rate is not predestined and is affected by factors such as the environment, nutrition, and management. Latest research shows that "bigger is better," as heavy and tall Thoroughbreds sold for the highest prices at yearling sales and when raced had the most earnings, graded stakes wins and grade-1 stakes wins (Pagan et al., 2005; Brown-Douglas and Pagan, 2006). Horses are therefore grown to be as large as possible at a young age, despite not achieving their mature weight and height until around four or five years of age. Unlike meat-producing animals, achieving maximal size in the least amount of time is undesirable in the horse as there are many career-ending developmental conditions such as osteochondritis dissecans (OCD) that occur in rapidly growing horses. Growing a foal too slowly, however, can prevent the animal from ever reaching its mature size. Optimal growth rate results in a desirable body size with the least amount of developmental problems, making the art of raising a successful athlete a sensitive balancing act. Kentucky Equine Research (KER) has studied Thoroughbred growth and development over the last 20 years. Body weight and height data have been collected from foals born and raised in the major Thoroughbred-producing countries of the world including the United States, England, Ireland, Australia, New Zealand, South Africa, and India. Using this database of over 15,000 Thoroughbred foals, KER has compiled detailed reference growth curves for breeders to use when monitoring their horses' growth. Using Gro-Trac, KER's innovative growth and ration management software, breeders can track and compare the growth rates of their horses to the average growth parameters of a chosen reference peer group. KER studies have also focused on the effects of nutrition and management on equine growth. This paper will review the major results of KER's growth and development research and discuss the various management factors that influence the growing horse from foal to athlete.
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