Nutritional- and suckling-mediated anovulation in beef cows 1

Nutrient intake, body energy reserves, and suckling are major regulators of reproductive performance of beef cows. Inadequate body energy reserves at parturition increase the interval to first estrus and ovulation, and postpartum nutrient intake can influence the duration of the interval in cows with thin to moderate body condition score. Suckling can increase the postpartum anestrous interval in thin cows, but has little effect on mature cows with adequate body energy reserves. The purpose of this review is to evaluate signals by which nutrient intake and body energy reserves may regulate ovarian function in postpartum beef cows. Nutritional restriction causes decreased secretion of GnRH and LH, reduces follicular growth, and decreases concentrations of estradiol in plasma. In addition to direct and indirect effects of decreased energy intake on the hypothalamus and pituitary, nutrition may influence ovarian function. Metabolic signals that communicate the adequacy of body energy reserves and nutrient intake may stimulate changes several weeks before ovulation occurs, have a permissive role, be regulated by binding proteins or receptors, or interact with stimulatory or inhibitory factors produced by adipose tissue. Metabolic signals may also have autocrine and/or paracrine effects. Adequate body energy stores and sufficient plasma concentrations of metabolic signals are prerequisites for ovulation in postpartum cows. Complex interactions between hormones, metabolic compounds, and other factors control follicular maturation, estrus, and ovulation in postpartum beef cows.