EFFECT OF INCREASED POSTMILKING PROLACTIN CONCENTRATIONS ON LACTATION, PLASMA METABOLITES, AND PANCREATIC HORMONES IN LACTATING GOATS

Six lactating dairy goats were utilized in a replicated 3 x 3 Latin square design to examine the effect of increased post-milking prolactin concentrations on lactational performance. Thirty minutes after each milking, either placebo or pituitary-derived ovine prolactin at 2 mg/h or 4 mg/h was infused via jugular cannula for 2 h. Goats were housed in a controlled environment at 19-degrees-C and a cycle of 16 h light and 8 h dark. Mean plasma prolactin concentrations after milking were increased 100 and 180% for 2 and 4 mg/h prolactin infusion, respectively. Milk yield was slightly but significantly increased by 2 mg/h prolactin infusion compared with placebo and 4 mg/h prolactin infusion. However, milk composition and yields of milk components were not influenced by treatments. No differences in dry matter intake, digestibility of the diet, or N retention were observed. Circulating concentrations of glucose, nonesterified fatty acids, insulin, and glucagon were not altered.