Protein metabolism in the lactating sow

A series of experiments were conducted to examine factors affecting feed intake and protein metabolism in the lactating sow. The primiparous sow exhibits poor appetite during the initial phase of lactation in relation to her requirements for production. The early phase of lactation is associated with a high plasma tryptophan to branched-chain amino acid (BCAA) ratio. High plasma tryptophan to the branched chain amino acids is associated with increased tryptophan entry in the brain and serotonin secretion which in turn is involved in the depression of feed intake in other species. The effect of decreasing the ratio of tryptophan to the BCAA in the sow did not increase feed intake, but rather decreased it. The leaner genotype sows tended to respond to an increased dietary BCAA by minimizing body weight loss during lactation.Body composition during pregnancy was also examined as a factor affecting protein metabolism and feed intake during lactation. Body weight change, feed intake and protein degradation rates were affected by the gestation body weight gain. Gilts fed at a high energy level during pregnancy, 36% above recommended levels from NRC (1988), exhibited a reduced insulin response to feed intake during mid-gestation. During lactation, these gilts also demonstrated a low post-absorptive insulin concentration, insulin to glucagon molar ratio, and a high post-absorptive glucagon concentration. These factors were associated with a decreased feed intake throughout lactation, and an increased protein breakdown rate as measured by plasma three-methylhistidine kinetics.Another experiment confirmed that high-energy-fed gilts during gestation demonstrated a decreased responsiveness to insulin and a reduced tolerance to glucose prior to parturition, further confirming the altered protein metabolic activity in response to excess energy intake during pregnancy.A novel approach to quantify daily amino acids uptake by the lactating mammary gland was examined. A technique to cannulate the anterior venous system of the mammary gland was developed and daily amino acid extraction rates and uptakes were measured and estimated, respectively. Extraction rate for the first limiting amino acid, lysine, increased with advancing lactation. Valine was shown to be extracted at low rates due to its high arterial concentration. New amino acid requirement estimates are proposed, based on the mammary uptake approach.U of I OnlyETDs are only available to UIUC Users without author permissio