METABOLIC STATUS AND INTERVAL TO FIRST OVULATION IN POSTPARTUM DAIRY-COWS

For 21 postpartum dairy cows studied during the period of negative ene rgy balance, the rate of muscle protein degradation, gluconeogenic cha nges, circulating large neutral AA, and plasma IGF-I were measured to investigate their possible association with the duration of anovulatio n and LH secretions. Cows that ovulated (n = 17) were energetically de ficient at first ovulation but were approaching a balanced state. The dynamic changes in energy balance, but not the mean energy balance or the extent of BW loss, were correlated with days to first ovulation. V ariations in energy balance were explained largely by variations in en ergy intake. Increased mobilization of body protein was indicated by h igher concentrations of 3-methylhistidine during the first 3 wk postpa rtum and was not correlated with duration of postpartum anovulation. P lasma aspartate transaminase decreased significantly, and the proporti on of Tyr to total large neutral AA significantly increased in the 12 d prior to first ovulation; both were correlated with LH secretion. Pl asma IGF-I did not correlate with days to first ovulation, but correla ted with LH pulse frequency. These findings indicate that decreased gl uconeogenesis from AA is associated with duration of recovery and that Tyr may participate in metabolic signaling to the hypothalamus-hypoph yseal axis controlling ovarian function in the postpartum dairy cow.