ENERGY-BALANCE AND PULSATILE-LH SECRETION IN EARLY POSTPARTUM DAIRY-CATTLE

The relationships between energy balance (EB), pulsatile LH secretion and circulating levels of insulin and various energy metabolites were assessed in ten lactating Holstein cows. Cows were blood sampled every 12 min via indwelling jugular catheters for 8 hr twice weekly beginning in the first week postpartum (PP) through first ovulation (1stOV). Days to negative EB nadir and days to 1stOV were highly correlated (P < .02). LH pulse frequency (P < .01), LH baseline (P < .05) and mean LH (P < .1) increased, while LH pulse amplitude tended to decrease when comparing the frequent sampling series immediately before and after the negative EB nadir. Plasma levels of non-esterified fatty acids (NEFA, r = -.40, P < .01), insulin (r = .38, P < .01), glucose (r = .31, P < .01) and beta-hydroxybutyrate (r = .19, P < .06) were correlated with EB. For within animal comparisons, NEFA was significantly correlated (r = -.44 to -.89, P < .05) with EB in 8 of 10 cows, but no other correlations were significant. Additionally, none of the metabolites nor insulin were significant in multiple regression models for 1stOV. Therefore, it appears that pulsatile LH secretion is suppressed until the negative EB nadir is reached, at which time LH pulse frequency increases stimulating 1stOV. Since NEFA and EB are directly related, NEFA may serve as a peripheral signal of EB to the central nervous system. © 1990.