Analysis of Variation in Some Factors Affecting Multiple Ovulations in Holstein Cattle

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Abstract
SUMMARY A total of 790 parities (728 noncystic and 62 cystic) covering 3,549 ovula- tions was analyzed for effects of sire-line, system of mating, parity, cystic con- dition, and individuality of the cow on the incidence of multiple ovulations. Sire-line had no significant influence. Frequency of multiple ovulations increased in association with the cystic condition and with increasing parity. Outbreds had a significantly higher incidence of multiple ovulations than inbreds. A highly significant repeatability (0.07) within a cow also was noted. The effects of both environmental and genetic factors on the rate of twinning in cattle have been studied (1-7, 10, 11), but little attention has been given to the influence of these factors on the incidence of multiple ovulations. Kidder et al. (8) made a preliminary examination of the influences of sire-line, parity, and interval since calving on multiple ovulations, but failed to find them to be significant. The purpose of the present study was to analyze the variation in the rate of multiple ovulations on more ex- tensive data collected later on the same herd as studied by Kidder et al. (8). EXPERIMENTAL PROCEDURE