Decreasing the Postcalving Anestrous Period in Suckled Beef Heifers

The interval from calving to first ovulation was reduced to less than 45 days in 2-year-old suckled heifers by feeding a high energy diet (ADG, 1.4-2.5 lb/day) during the postcalving period or by a single injection of exogenous gonadotropin (2,250 IU PMSG) on day 42 postcalving. A comparison of reproductive parameters for heifers on the high and low energy (maintenance) diets during the postcalving period indicated that a higher percentage of heifers on the high energy diet had ovulated by 46 days postcalving (100 vs 0 %) and that both basal plasma luteinizing hormone (LH) concentration and estrogen-mediated LH release was increased during the early postcalving period. Results of these experiments suggest that the level of endogenous gonadotropin secretion may determine the length of the postcalving anestrous period and that plasma LH may be a useful parameter in establishing nutrition requirements for the postpartum lactating cow