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Reproductive Efficiency on Fourteen Horse Farms¹

Virginia Polytechnic Institute, Research Division Blacksburg

Abstract

Reproductive efficiency was estimated from breeding records involving 1,876 mare-years on 14 farms and six breeds for the period 1960–64. Conception, foaling and weaning efficiency means were 80.1%, 73.8% and 70.8%, respectively. Individual service data on 1,027 mare-years indicated mean breeding frequency ratios of 1.71 period/mare-year, 2.75 services/mare-year and 1.61 services/period. Considerable variation in efficiency between years and farms was noted. Lactating, barren and maiden mares averaged 79.5%, 72.5% and 78.6% conception, respectively. The conception rate varied seasonally, being very low in January and February, rising to a peak in May and declining gradually there after. The conception efficiency of young mares fluctuated until age 7, reached a peak of 89.6% at age 9, remained on a plateau above 70% until age 15, and declined thereafter. On each of four Thoroughbred farms, an unexplained sharp decline was noted for the sixth year. The incidences of complete anestrus and twinning were low, 0.60% and 1.1%, respectively.

¹ Published with approval of the Director. Agricultural and Life Sciences.