Reproductive performance of Thoroughbred mares in the Waikato region of New Zealand: 1. Descriptive analyses

Abstract

AIM: To describe the reproductive performance of a population of Thoroughbred mares on stud farms in the Waikato region of New Zealand. METHODS: A prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during three consecutive breeding seasons (2006–2008). A total of 1,482 individual mares contributed 2007 mare years and 3,402 oestrous cycles over the three breeding seasons. Mares were served by 87 individual stallions. RESULTS: The mean first-cycle pregnancy rate (FCPR) was 53.6%, the end-of-season pregnancy rate (SPR) was 85.3% and the foaling rate was 80.2%. There were significant differences amongst farms for FCPR (range 47.3–68.2%; p<0.01), SPR (range 81.4–92.6%; p<0.001) and foaling rate (range 77.8–90.1%; p<0.001). There were significant differences amongst stallions in their FCPR (range 38–74%; p<0.001) and SPR (range 72–97%; p<0.001).The proportion of pregnancies lost between day 14–16 and day 42 of gestation was 5.5% and the proportion of pregnancies lost between day 42 and term was 3.0%. Mares older than 14 years of age and barren mares had the highest pregnancy loss rates. Of all pregnancies diagnosed at 14–16 days, 12.9% were multiple pregnancies. The length of the breeding season was relatively short with 87.3% of services occurring in the 91-day period between 1 September and 30 November. CONCLUSIONS: The reproductive performance of Thoroughbred mares in the Waikato region of New Zealand was similar to that reported from other major Thoroughbred breeding countries. Although the per-cycle pregnancy rates in this study were lower than those reported in some studies, the foaling rate was similar to previous reports and this was achieved during a relatively short breeding season.