The effect of dioestrus on the racing performance of Greyhounds.

The degree of performance change during the dioestrus of racing Greyhounds has long been the subject of debate. Assessments have previously been on a qualitative basis. The analyses in this paper are unique and produce a quantitative assessment of the change in performance during dioestrus. By accessing a large dataset, race form and oestrous data were analysed using a longitudinal observational study design. The performance changes in dioestrus were modelled with a series of multilevel linear regressions revealing a pattern such that the performance loss varied from 0.031 to 0.733 s (90% confidence interval) between 41 and 56 days since oestrus over 450 m, returning to the baseline (anoestral) performance level after about 80-100 days. The changes in performance formed a temporal match with the changes in serum progesterone concentration noted by other workers. Whilst serum hormone concentrations were not measured, it is suggested that the performance changes are linked with the changes in serum progesterone concentrations rather than prolactin. It is therefore proposed that a minimum time off of 70 days could be set, which would capture the majority of females with a genuine change in performance, and with a caution regarding the use of entire female Greyhounds for performance studies.