Quantification of equine reproductive loss A survey on the New Zealand Thoroughbred broodmare

Abstract

To describe the biological risk factors for reproductive losses within the New Zealand commercial Thoroughbred horse breeding industry reproductive data of 1270 mares for the 2001/02 to 2008/09 breeding seasons were obtained from online databases and collated for analysis. Data were examined using Chi square tests, logistic regression and Kaplan Meier survival analysis. The effects of mare age, parity and status on the rates of pregnancy losses were analysed. The overall pregnancy rate and foaling rate was 83.9% and 80.5% respectively. Mare age and status significantly affected the incidence of misses and slips. Old mares (13-18) showed more slips and an increasing risk for missing. This risk does not increase in mares older than 12 years. Mares with a dead foal the previous year had a major decrease in pregnancy rate, while mares that were not served and maiden mares showed the highest pregnancy rates. No prospective value of having a miss or a slip one year is observed, so a missing or slipping mare is not likely to miss or slip more than foaling mares during the rest of their careers. Embryonic loss in New Zealand Thoroughbred broodmares can be caused by a wide range of factors, directly or indirectly. More integrated research is needed to specify the risks. Stud masters must be aware of the risks and make sure that mares that gave birth to a dead foal are carefully examined. Older mares need to be inspected thoroughly to minimise embryonic loss.