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The Estrual Cycle of the Mare^*

A Preliminary Report

Missouri Agricultural Experiment Station, Montana Agricultural Experiment Station, and the United States Department of Agriculture, Cooperating

Abstract

Increased interest in the measurement and control of fertility and the correction of sterility has emphasized the importance of an understanding of the behavioral and physiological events of the estrual cycle. This study was undertaken with the hope that it might contribute to the knowledge already available concerning the estrual cycle of the mare.

Materials and Methods: Data on estrus, ovulation and related phenomena in the mare were obtained at the United States Range Livestock Experiment Station, Miles City, Montana, between April 20 and July 10, 1937 and April 20 and July 15, 1938. The findings are the results of observations on 45 draft (chiefly grade Belgian) and 35 light (chiefly grade Thoroughbred) mares. All mares were teased once daily by active, healthy, vigorous stallions, and the reactions of the mares recorded as described by McKenzie and Andrews (1937). The ovaries of all mares were palpated per rectum once daily estrus, and those of selected mares were examined at 5–7 day intervals during interestrus.

^* Contribution from the Department of Animal Husbandry, Missouri Agricultural Experiment Station, Journal Series No. 624.

^** The authors wish to express their appreciation to Dr. E. B. Osborn, Mr. J. R. Quesenberry, Mr. Frank King, and other members of the staff at the U. S. Range Livestock Experiment Station for the cooperation which they have given in making this study possible.