Glucogenic and hormonal responses to abomasal casein and ruminal volatile fatty acid infusions in lactating goats

To determine responses to abomasal protein infusion and ruminal acetate: propionate ratios, four lactating Toggenburg goats fed hourly a 70% roughage and 30% concentrate diet were used in a Latin-square design with a factorial arrangement of treatments. Either acetate or propionate was infused ruminally and casein or saline infused abomasally. Estimated net energy and volume of the infusates were similar for all treatments. To examine the effects of treatments on glucose metabolism, 2-carbon-14 propionate was infused ruminally and 6-hydrogen-3 glucose was infused intravenously for 9 and 5 h, respectively. Although glucose concentration in plasma was higher and propionate turnover greater with propionate treatment, percentage of glucose derived from propionate, amount of propionate coverted to glucose, and glucose turnover remained unchanged. No differences in glucose metabolism due to the abomasal casein infusion were evident. To determine the effects of treatment on insulin, glucagon, growth hormone, and prolactin in plasma, samples were collected at 10-min intervals for 3 h at 0400 and 1600 h. No diurnal variation or consistent peaks were observed for any of the hormones nor were treatment effects on plasma concentrations of insulin, growth hormone, or prolactin evident. Glucagon concentration was higher with casein treatment; however, no relationship existed between glucagon in plasma and glucogenic parameters measured.