The experiment included six studies to show various mechanisms by which soybean meal provides superior growth performance compared to canola meal or corn-DDGS in reduced-protein diets. Diet protein was reduced by 4% relative to recommended and supplemented with essential and some nonessential amino acids. The 4% reduction in protein involved reducing soybean meal by 10%. Soybean meal inclusion was further reduced by 5% and replaced with 8 or 10% of canola meal or corn-DDGS, and the birds were challenged with coccidiosis on day 15 of age. Growth performance, amino acid digestibility, immune response, protein synthesis and degradation, microbial profile, and antimicrobial resistance were studied. The results showed that the difference in weight was marginal for birds receiving the different protein feedstuffs. However, in the coccidiosis-challenged group, the birds fed soybean meal consistently had greater weight gain and lowest FCR compared to the other groups. The same pattern was observed for amino acid digestibility. A more robust immune response was also observed for the broiler chickens that received the soybean meal diet in the low-protein diets.

We showed the advantage of using soybean meal compared to alternative and competitive protein feedstuffs. The results from the studies showed that even when diets are formulated to be lower in protein content beyond the current recommendation, soybean meal still produces superior performance. This was especially evident when birds were challenged with coccidiosis, a common poultry disease. The observation that the immune response was more robust in birds that were fed soybean meal compared to the competitive protein feedstuff is excellent support for the observation of the growth performance effect.