Inhibition of ovulation in the postpartum cow and the lactating sow

Increased genetic selection and 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 8-10 weeks of early lactation. NEBAL delays the timing of first ovulation through attenuation of LH pulse frequency and low levels of blood glucose, insulin and IGF-I that collectively limit oestrogen production by dominant follicles. NEBAL results in mobilization of adipose tissue and loss of body condition score (BCS), which is strongly associated with the length of the postpartum anovulatory period. Failure of ovulation of the first wave dominant follicle is associated with elevated nonesterified fatty acids and ketones in plasma and greater accumulation of triglycerides in the liver during the first 3 weeks of lactation. NEBAL is related to lower fertility in dairy cows both through inhibition of ovulation in early lactation and effects exerted later during the breeding period. Management strategies to minimize the inhibitory effects of NEBAL on first ovulation should begin during the prepartum transition period and include maintaining moderate BCS and energy intake through parturition. Modern sows have been improved genetically for higher productivity including ovulation rate, litter size and milk production. Peak milk yield is achieved within 10 days after farrowing with consequent massive mobilization of body fat and protein mass. Conservation of body protein mass (< 12% loss) during the first lactation minimizes the weaning to estrus interval by advancing ovarian follicular development toward ovulation. The lysine requirement in early lactation is extraordinary. Plasma insulin and IGF-I concentrations seem unrelated to the observed differences in ovarian follicular development. Overall, NEBAL inhibits ovulation in both high producing cows and sows, but there are species differences in response to protein losses and hormonal interactions. (c) 2005 Elsevier B.V. All rights reserved.