Participation of Victorian Thoroughbreds in the racing industry: a whole‐of‐population benchmark

Abstract

The proportion of Thoroughbred (TB) horses that commence training and eventually race, is an important industry-level indicator of how successful it is at producing horses suitable for racing. It is also of interest to the wider community and is central to the issue of whether there is overbreeding in the Australian TB industry. This study investigated the training and racing records for the 2005 and 2010 Victorian TB foal crops to determine the proportion of TBs that train and race, and the age of entering training and first race start. Subsets of the foal crop were also examined to determine if premier yearling sale cohorts would produce selection bias. The Australian Stud Book (ASB) registered 7662 TB horses born in Victoria in 2005 (n = 4116) and 2010 (n = 3546). Of these, 5614 (73%) entered training and 4868 (64%) started in at least one race. Fourteen percent (n = 1045) of the study cohort had their first race start as 2-year-olds and 35% (n = 2644) had their first start as 3-year-olds. A higher proportion of TB horses that attended premier yearling sales entered training (93%) and raced (84%). This study established a baseline for training and racing milestones, such as the proportion and age that horses commenced training, and age of first start using population-level data. It also established that the use of subsets of the population can introduce selection bias.

Inbreeding depression and the probability of racing in the Thoroughbred horse

“…Race records (up to the end of the 2020 racing season) were retrieved for n = 6128 of these horses that were born in Europe (EUR) and Australia and New Zealand (ANZ) prior to and including 2015, and were therefore at least five years old. Among horses that race, the majority have their first start before they are five years old [ 22 ], and the median age of retirement from racing has been reported as five years old [ 19 ]. Horses were assigned as ‘raced’ ( n = 3038, EUR, n = 2282 ANZ) if they had at least one start before five years old or ‘unraced’ ( n = 606 EUR, n = 202 ANZ) if they had no recorded race start before five years old.…”

“…The number of races that an individual horse participates in and a horse's career duration are considered key indicators of animal health [ 25 ]. At a population level, it has been proposed that the success of the Thoroughbred industry may be measured by the proportion of horses born that commence racing [ 22 ].…”

“…In Thoroughbreds, a lower-than-expected mutational load has led to the hypothesis that existing selection processes are effective in purging deleterious mutations [7]. This may be facilitated by the unusually large census population size relative to the effective population size [5]; for instance, although racing is the breeding goal, a high proportion (35-50%) of foals born never race [18][19][20][21][22] and a small proportion enter the breeding population (less than 5% of males and 50% of females). While this selection may purge large-effect mutations it is expected that even at low frequencies, segregation of deleterious alleles within a population with a low effective population size will have consequences for some aspects of population viability [8] and inbreeding depression is likely to be persistent even with ongoing purging [15].…”

Factors associated with racing performance and career duration for Victorian‐born Thoroughbreds

“…Previous research investigating TBs born in Victoria in 2005 and 2010, found the proportion of horses that raced from the 2010 foal crop was 3% less than those born in 2005. 21 While that percentage is relatively small, combined with a 13% reduction in the number of TBs born means there are less horses participating in the number of races expected each week by the general public. 21 The reduced number of horses entering racing may lead to a number of flow-on effects for the industry as a whole, but it may also require changes to the management of horses in its care.…”

“…21 While that percentage is relatively small, combined with a 13% reduction in the number of TBs born means there are less horses participating in the number of races expected each week by the general public. 21 The reduced number of horses entering racing may lead to a number of flow-on effects for the industry as a whole, but it may also require changes to the management of horses in its care. Benchmarking individual horse performance at the population level will allow the industry to document trends over time.…”