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Stimulation of Follicular Activity and Estrous Behavior in Anestrous Mares with Light and Temperature^{1, 2,}

University of Wisconsin, Madison 53706

Abstract

Two groups of pony mares were housed for 120 days beginning October 17 in controlled environment rooms in the University Biotron. Temperature and daily photoperiod were programmed to simulate outdoor conditions in southern Wisconsin for either October 17 to February 15 (control group, six mares) or March 1 to July 1 (treated group, seven mares). All mares were given a maintenance diet of a commercial feed. Ovarian follicular development was monitored by rectal palpation and the incidence of estrus was monitored daily by teasing with a stallion. After 63 days of treatment, there were more (P<.05) total palpable follicles (>10 mm diameter) in the treated mares. By day 60, diameter of the largest follicle was greater (P<.05) in treated mares. By day 69, all ovarian end points (diameter of largest follicle, total number of follicles, number of follicles >20 mm, and average follicle diameter) were significantly greater in treated mares than in controls. The changes for each ovarian end point in treated mares were best characterized by a significant cubic regression curve with a steep central portion (sigmoid curve). In treated mares, estrous behavior was shown in four of seven by the 94th day, and in seven of seven by the 112th day. None of the control mares exhibited estrus during the entire project. Two of seven treated mares ovulated by the project termination date; no control mares ovulated.

¹ Research supported by the College of Agriculture and Life Sciences and the Graduate School, University of Wisconsin, Madison and by Grant No. 2-T01-HD-00104-06 from the National Institutes of Health and Grant No. 630-0505A from the Ford Foundation.

² Florida Agricultural Experiment Station. Journal Series No. 5788.

³ Present address: Horse Research Center, Animal Science Department, University of Florida, Gainesville 32611.