Responses of Barrows Consuming a Diet Formulated on an Ideal Protein Basis at Different Feeding Levels

1998 University of Nebraska-Lincolnd Extension Swine Report. An experiment was carried out to evaluate the performance, nutrient digestibilities and plasma metabolites of barrows fed with a corn-soybean meal diet (CONTROL) or a diet formulated on an ideal protein basis (IDEAL; supplemented with crystalline lysine, threonine, tryptophan and methionine). Each diet was offered either on an ad libitum basis or at a feeding level of 90 or 80 percent of ad libitum feed intake. Averaged for the entire experimental period, barrows fed the CONTROL diet gained seven percent faster (P < .05) and were five percent more efficient (P < .01) than barrows fed the IDEAL diet. As the level of feed intake decreased, there was a decrease in daily gain (P < .01), but feed efficiency tended to be improved (P < .10) for barrows fed 90 percent of ad libitum. The apparent digestibilities of dry matter and energy were approximately three percent greater (P < .01) for barrows fed the IDEAL diet. Plasma urea concentrations were lower in barrows fed the IDEAL diet, regardless of feeding level; however, for barrows fed the CONTROL diet, the urea concentration was lower when the feeding level was 80 percent of ad libitum (diet x level, P < .01). Over time, the urea concentration declined in barrows fed the IDEAL diet (diet x time, P < .01). The concentrations of plasma glucose were lower in barrows fed the CONTROL diet (P < .01), were reduced with each reduction in the feeding level (P < .01), and were diminished over time throughout the experiment (P < .01). Plasma nonesterified fatty acid concentrations were lower in barrows fed the CONTROL diet at the beginning of Phase 2 (diet x time, P < .05). The reduction in daily gain observed with the IDEAL diet suggests a deficiency of other essential amino acid(s) may have limited the growth potential of these pigs or that the ideal pattern was not correct for the pigs used in this research. Results from this study will help to provide a basis for future studies to investigate the apparent reduction in performance sometimes observed in pigs consuming lower protein, amino acid-supplemented diets. We recognize the reduction in growth performance observed for the IDEAL diet may be offset by changes in body composition.