Reproductive performance of Thoroughbred mares in the Waikato region of New Zealand: 2. Multivariable analyses and sources of variation at the mare, stallion and stud farm level.

Abstract AIM: The objective of this study was to utilise multivariable statistical methods appropriate for clustered data to identify mare-related explanatory variables that significantly affected the reproductive performance of Thoroughbred mares in the Waikato region of New Zealand. In addition, we aimed to determine the relative contribution of the mare, stallion and stud farm to reproductive performance. 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. Reproductive performance was measured using three parameters; (a) first-cycle pregnancy rate (FCPR), (b) end-of-season pregnancy rate (SPR), and (c) the start-of-mating to conception interval. RESULTS: When controlled for the effects of serving stallion, stud farm and year of study the only significant mare-related va...