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Energy Intake Regulates Ovarian Function in Beef Cattle¹

Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater 74078

^2. Correspondence: phone: 405-744-6077; fax: 405-744-7390; E-mail: rpw{at}okway.okstate.edu.

Abstract

Nutrient intake and body energy reserves are major regulators of reproductive performance of beef cows. Reduced body weight causes cessation of estrous cycles, and inadequate body energy stores at parturition prolong the postpartum anestrous interval. Nutritionally induced reduction in follicular growth is a result of decreased secretion of GnRH and LH. During anestrus, ovarian follicular waves are recurrent, but inadequate estradiol is secreted by the dominant follicle to cause estrus and ovulation. Realimentation of nutritionally induced anovulatory cows results in larger dominant follicles and ovulation occurs when body energy stores are adequate. Increased follicular growth rate is associated with increased concentrations of LH, estradiol, and IGF-I in plasma. When nutritionally induced anovulatory cows are realimented, ovulation and a corpus luteum with shorter than normal function occurs, usually without estrus, before the first normal estrous cycle. In addition, exogenous GnRH infusion induces ovulation in nutritionally induced anestrous cows. We conclude that prolonged restriction of nutrient intake reduces secretion of LH and IGF-I, less estradiol is produced by the dominant follicle, and ovulation ceases. Realimentation of anestrous animals alters metabolic signals, resulting in pulsatile LH secretion, increased size of the dominant follicle, and ovulation.

^1. Approved for publication by the director, Oklahoma Agric. Exp. Sta. The authors are grateful to L. J. Spicer and C. A. Lents for their comments on this manuscript.