Influence of nutrition, body condition, and metabolic status on reproduction in female beef cattle: A review.

Nutrition is of fundamental importance in reproductive function of female beef cattle. Nutrition determines live weight (LW) and body condition score (BCs) and both were found more than 50 years ago to underpin fertility in pubertal heifers and postpartum cows. In heifers, LW at weaning and average daily gain (ADG) after weaning determines age and LW at puberty, and subsequent lifetime fertility. In cows, BCS at parturition is the most important factor that determines the period to re-conception postpartum. Nutrition establishes systemic metabolic homeostasis. Metabolic hormones such as leptin, IGF1 and Ghrelin act as signaling factors that regulate activity of GnRH neurons in the hypothalamus. The release of GnRH and function of the reproductive endocrine system is determined by the balance of positive signals (IGF1, leptin) and negative signals (Ghrelin) at GnRH neurons. Nutritional factors also directly influence ovarian follicles, oocytes and embryos. Saturated fatty acids (FAs) are detrimental to oocytes and embryos whilst unsaturated FAs may be beneficial. The ratio of FAs (saturated, monounsaturated, polyunsaturated) is likely the key to optimal reproductive function. Nutrition controls the levels of metabolic hormones (leptin, IGF1, Ghrelin) and metabolic factors (FAs) and both have major roles in reproduction in female beef cattle.