Influence of Dietary Energy Intake on Bovine Pituitary and Luteal Function

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Abstract
Three experiments were conducted to measure the effect of dietary energy intake on pituitary and luteal function. Intact cows and heifers and spayed cows were administered injections of gonadotropin releasing hormone (GnRH) following a prolonged period of either dietary energy restriction (low energy) or adequate energy (high energy) intake to determine if energy intake influenced the pituitary responsiveness to GnRH. In addition to measuring luteinizing hormone (LH) release following GnRH, peripheral serum concentrations of progesterone, luteal progesterone content and the pituitary LH content of cows fed low and high energy levels were compared. Low energy increased the LH release after a GnRH injection in intact heifers but not in intact cows. Peripheral serum progesterone concentrations tended to be reduced in low energy heifers and cows. Low energy spayed cows released more LH in response to GnRH than adequate energy spayed cows. Therefore, an increase in the LH release after a GnRH injection was observed despite removal of ovarian steroids. Restricting energy intake increased the pituitary LH content of spayed cows but decreased the pituitary LH content of intact cows. The release of LH following five consecutive injections of GnRH declined nonlinearly after the first injection in both low and high energy fed heifers. Conclusions from these results were that dietary energy restriction may influence the LH release directly at the pituitary level as well as indirectly through effects on ovarian steroid production. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.