SERIAL MEASUREMENT OF PERIPHERAL ESTROGEN AND PROGESTERONE CONCENTRATIONS IN ESTROUS MARES TO DETERMINE OPTIMUM MATING TIME AND DIAGNOSE OVULATION

Rapid enzyme-based immunoassays were used to measure concentrations of oestradiol-17 beta and progesterone in daily blood samples recovered throughout oestrus and for a few days after ovulation from 34 Thorough bred and 8 pony type maiden, barren and foaling mares, The first decte ctable fall in oestradiol-17 beta levels occurred in 88% of the mares within the interval -72 to 0 h with respect to ovulation and in 65% of mares within the interval of -48 to 0 h. The results indicated that s erial daily hormone assays of this type could, in a high proportion of animals, predict a correct time for a single mating and diagnose the occurrence of ovulation in Thoroughbred mares at stud in the absence o f the present management system which includes repeated veterinary exa minations of the ovaries, However, the absolute need for serial daily sampling from all mares to produce interpretable hormone profiles, and the cost of this sampling and the hormone assays, make the method imp ractical at the present time.