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In-Breeding Impact Is Insignificant
Research by PhD student Kao Castle (supervised by Sydney University's Professor Frank Nicholas using data provided by the Australian Stud Book) has shown a relatively low rate of increase in thoroughbred in-breeding over the past 20 years: the co-efficient has risen from 12.9% to only 14.3%. In-breeding is the practice of breeding between relatives & the inbreeding co-efficient indicates the proportion of genes inherited from each parent that are identical by descent. Over generations in-breeding leads to a reduction in generic variability & increased sameness, which causes reduced health & fitness in the population, increased incidence of hereditary disease & decreases in reproductive performance. Michael Ford, Keeper Of The Australian Stud Book, commented: "The low increase rate suggests breeding practices over the last 20 years have not posed a threat to the generic well-being of the Australian thoroughbred." These practices include: use of shuttle stallions (averaging 64 each year); increased number of mares covered by a stallion (averaging 10 in 1986 & now 28); & more stallions covering over 100 mares (24 in 1997 & now 73). Castle believes the use of shuttle stallions has positively influenced the average in-breeding co-efficient, because breeders used overseas stock to diversify the generic background of their foals. She reported: "There is likely to be no significant effect on increasing the in-breeding co-efficient as long as breeders diversify with overseas born sires." The research also found that in 2000, 63% of all thoroughbred foals born in Australia had an overseas parent (compared with 56% in 1990). And between 1990-2005, foals born with at least 1 overseas parent "were on average less in-bred than their colonial equivalents".