Changes in metabolic and reproductive characteristics associated with lactation and glucose infusion in the postpartum ewe.

This study examined mechanisms whereby the metabolic environment interacts with basic reproductive function. Ewes lambing during the breeding season were fed to maintain (MAINT, n = 10) or gain (GAIN, n = 11) body weight during the last 4 mo of gestation. From d 7 to 22 postpartum, ewes were infused iv with saline (n = 10) or glucose at a rate calculated to increase normal glucose entry rate by 75% (n = 11). Blood samples were collected daily to determine plasma concentrations of nutritive metabolites and insulin and at frequent intervals on d 14 and 21 to determine serum gonadotropin concentrations. Hypothalami and pituitaries were collected on d 22 to determine hormone content and receptor concentrations. Plasma concentrations of nutritive metabolites and insulin indicated that MAINT ewes mobilized more (P less than .01) body fat and protein reserves during gestation and early lactation than ewes in the GAIN group. Glucose infusion elevated plasma concentrations of glucose (P less than .05) and insulin (P less than .07) and reduced (P less than .05) fat and protein mobilization, even though it depressed feed intake (P less than .001), compared with saline infusion. Hypothalamic gonadotropin-releasing hormone (GnRH), pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) content and pituitary GnRH receptor concentration were similar between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)