Metabolic status and interval to first ovulation in postpartum dairy cows.

For 21 postpartum dairy cows studied during the period of negative energy balance, the rate of muscle protein degradation, gluconeogenic changes, circulating large neutral AA, and plasma IGF-I were measured to investigate their possible association with the duration of anovulation and LH secretions. Cows that ovulated (n = 17) were energetically deficient 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. Variations in energy balance were explained largely by variations in energy intake. Increased mobilization of body protein was indicated by higher concentrations of 3-methylhistidine during the first 3 wk postpartum and was not correlated with duration of postpartum anovulation. Plasma aspartate transaminase decreased significantly, and the proportion of Tyr to total large neutral AA significantly increased in the 12 d prior to first ovulation; both were correlated with LH secretion. Plasma IGF-I did not correlate with days to first ovulation, but correlated with LH pulse frequency. These findings indicate that decreased gluconeogenesis from AA is associated with duration of recovery and that Tyr may participate in metabolic signaling to the hypothalamus-hypophyseal axis controlling ovarian function in the postpartum dairy cow.