PSII-19 Stallion exposure fails to alter circulating LH concentrations or hasten ovulation in seasonally anestrous mares

Abstract

Abstract Introduction of males to seasonally anestrous females has been shown to increase LH concentrations and hasten the first ovulation in ewes and does. Investigation of the male effect in mares has not been well-studied. The objective of this study was to determine if direct or indirect exposure to a stallion would result in a similar increase in LH and hasten first ovulation in anestrous mares. In late February, mares were stratified by parity and age and randomly assigned to 3 treatments (n = 7 per treatment): DXP (direct exposure; mares housed adjacent to stallion and allowed direct contact for 2 h on 3 d/wk by placing the stallion into a cage in the center of a tease pen), IXP (indirect exposure; mares housed adjacent to stallion but not allowed direct contact), and CON (control; mares housed away from stallion and not allowed direct or indirect exposure). During the first, third, and fifth days of treatment, blood was collected hourly for 8 h beginning just before treatment initiation for later analysis of LH. Concentrations of LH were analyzed for repeated measures and time from the first day of treatment to ovulation was analyzed using one-way ANOVA. The interval from treatment initiation to first ovulation did not differ (P > 0.05) among treatments: 36.3±6.7, 36.9±6.7, and 48.3±4.2 d for DXP, IXP, and CON, respectively. Although treatments did not affect (P > 0.05) LH concentration, a significant day effect (P < 0.05) was detected with LH concentrations being greater on the fifth treatment day compared with the first and third days. Results signify that stallion exposure to anestrous mares failed to elicit the same effects that have been observed in short-day breeders, thus indicating that stallion exposure may not be beneficial in the management of anestrous mares.