Energy balance relationships with follicular development, ovulation and fertility in postpartum dairy cows

Increased capacity for milk production in dairy cows has been associated with a decline in fertility. Following parturition,. nutritional requirements increase rapidly with milk production and the resulting negative energy balance (NEBAL) extends for 10-12 weeks. NEBAL is strongly associated with the length of the postpartum anovulatory period through attenuation of LH pulse frequency and low levels of blood glucose, insulin and IGF-I that collectively limit oestrogen production by dominant follicles. Plasma concentrations of IGF-I and IGFBP-3 are higher in cows with an ovulatory vs. nonovulatory first dominant follicle. Evidence has accumulated that links the metabolic demands of high milk production and associated NEBAL with diminished quality of oocytes and capability for embryo development. Also NEBAL and body condition score (BCS) loss are related to reduced serum progesterone concentrations during the breeding period and to lower pregnancy rates. Overall, NEBAL is related to lower fertility in dairy cows both through effects exerted early in lactation and later during the breeding period. (C) 2003 Elsevier B.V. All rights reserved.