The digestion and absorption of dietary protein was measured in weanling pigs (5 wk of age). Diets containing corn and either dried skim milk (DSM), soybean meal (SBM) or corn gluten meal (CGM) were fed for 7 d, and the contents of the stomach and six segments of the small intestine were collected. Nitrogen digestibility increased linearly from the proximal duodenum to the distal ileum, and was highest for DSM, intermediate for SBM and lowest for CGM diets at the distal ileum. The content of free amino acids in digesta increased 8-fold (SBM and CGM) to 12-fold (DSM) between the stomach and the proximal duodenum and reached a maximum concentration in the distal jejunum. Digestion of DSM was more proximal than was that of SBM. Although there was some accumulation of small peptides in the duodenum with a subsequent decrease in the jejunum, the molecular weight profiles of the soluble proteins were relatively constant throughout the small intestine. Protein solubility and the rate of proteolysis in the stomach and upper small intestine were the primary factors that limited the digestion of SBM and CGM.

SummaryOne-hundred-ninety-two weanling pigs from two separate trials, (initial weight 6.0 and 5.6 kg) and 400 growing-finishing pigs (initial weight 17 kg) were fed normal and high lysine corn diets containing four levels of lysine in a 2 • 4 factorial arrangement. Crossbred (Large White • Landrace x Duroc) pigs were used in all experiments. The objectives of the experiments were to (1) compare normal and high lysine corn when fed at different lysine levels, (2) determine the lysine requirements for the three stages of growth and (3) evaluate the effect of protein level on the lysine requirement. All diets were balanced on a lysine basis. The results indicated that both weanling and growingfinishing pig performance and final carcass composition were similar for pigs fed normal or high lysine corn diets balanced on a lysine basis. Weanling pigs from 5 to 14 kg required at least 1.10% lysine. Based on changes in body weight gain and feed efficiency, the lysine requirement of growing pigs (17 to 54 kg) was .70%, and that of finishing pigs (54 to 101 kg) was .50%. However, based on lean tissue growth rate (as reflected by longissimus muscle area and percentage of lean in the carcass) the requirement was at least .

Protein digestion and absorption were measured in weanling pigs (5 wk of age) using a total digesta collection procedure. In the first experiment, the objective was to measure the fate of nitrogenous digesta as it passed from the stomach to the terminal ileum when pigs were either allowed ad libitum access to feed or were fed four equal meals per day. Pigs were fed a standard corn-soybean meal diet in this experiment. There were no differences in flow rate or retention time of dry matter or nitrogen, and no differences in apparent nitrogen digestibility between the two feeding regimens. More than 80% of the soluble protein in the stomach and 65% in the small intestine was between 2,000 and 15,000 molecular weight. The molecular weight profiles of the soluble proteins were relatively constant throughout the small intestine, indicating that the products of protein hydrolysis were absorbed rapidly. The objective of the second experiment was to compare protein digestion and absorption in pigs fed a corn-soybean meal diet with those fed a protein-free diet. The molecular weight profiles of soluble protein were similar for the two groups of pigs. The data indicate that most of the endogenous enzymes were hydrolyzed rapidly, since little soluble protein corresponding to the molecular weight of pancreatic enzymes was detected.

Fifteen newborn pigs (1.5 kg) were used to estimate CO2 "production" over a 5-h experiment. In each piglet, the average expired air CO2 irreversible loss rate measured over 15-min intervals was compared with an estimate of CO2 "produced" by a continuous infusion of NaH14CO3 into either the aortic artery (seven pigs) or the portal vein (eight pigs). The specific radioactivity (Bq/mumol) of the expired CO2 taken over consecutive 15-min intervals during the 5-h period was fitted to an exponential model to predict the specific radioactivity at steady state. This specific radioactivity was used to calculate the total CO2 irreversible loss rate and to correct for the difference in tracer infused in relation to tracer excreted at 5 h (76 to 78%). The estimated CO2 "produced" tended to be higher (P < 0.12) when the aortal rather than the portal infusion site was used [571 vs. 498 mumol/(min.kg0.75)]. The isotope dilution technique significantly (P < 0.05) overestimated the expired air CO2 regardless of whether the aortal [571 vs. 469 mumol/(min.kg0.75)] or portal [498 vs. 447 mumol/(min.kg0.75)] routes of infusion were used.

Two metabolism studies were conducted with 24 (Exp. 1) and 36 (Exp. 2) crossbred barrows (initial weight 35 kg) to determine the effect of corn type -normal corn (NC) and high-lysine corn (HLC) -and storage method -dry (D), high-moisture (HM) and reconstituted (RC) -on energy and N digestibility. Diets fed in Exp. 1 were: 1, NC-soybean meal formulated at .78% lysine (dry matter basis); 2, HLC-soybean meal containing the same amount of corn as diet 1 (.87% lysine); 3, HLC-soybean meal with the same lysine level as diet 1. In Exp. 1, dry matter, energy and N digestibilities were not different between corn types or lysine levels (P>.16). These results indicate that energy and N digestibility of HLC in typical diets for growing swine are similar to those for NC diets when both are balanced on a lysine basis. Also, replacing NC with HLC on an equal-weight basis did not affect energy and N digestibility. In Exp. 2 six diets balanced on an isonitrogenous and dry-matter basis were tested. Normal corn and HLC diets, which had been stored by three different methods (D, HM and RC) were arranged in a 2 X 3 factorial plan. There were no differences between corn types in dry matter, energy and N digestibilities. The HM and RC treatments had larger particle sizes than the dry corn diets. For diets balanced on an isonitrogenous basis, dry corn storage improved energy digestibility (P<.10). Reconstitution appeared to improve energy balance and N digestibility of HLC, while HM storage improved energy balance and N digestibility of NC