Partial replacement of soybean meal by other protein sources on nutritional characteristics of beef cattle fed a whole corn grain diet

Diets composed of whole flint corn grain (WCG) without any roughage source are often used in South American countries. The primary source of protein in theses diets is soybean meal. We hypothesized that the combination of different protein sources improves ruminal fermentation and nutrient digestibility. This study was carried out to assess the impacts of replacing 50% of the soybean meal by other protein sources on voluntary dry matter intake (DMI), digestibility, efficiency of N utilization, efficiency of grain use, metabolic characteristics, and ingestive behavior of Nellore cattle fed WCG diets. Five rumen-cannulated Nellore Bulls (average BW = 651.6 ± 31.83 kg) were used in a 5 x 5 Latin square design, randomly assigned to five diets consisting of 85% of WCG and 15% of pellet supplement with combination of different protein sources: SM - pellet supplement with soybean meal only; CM - soybean meal and cottonseed meal; SFM - soybean meal and sunflower meal; DDG - soybean meal and DDG; DDGS - soybean meal and DDGS. The replacement of 50% of soybean meal by DDG increased (P<0.05) DMI and organic matter intake (OMI), both DMI and OMI were lower with CM. Digestibility, ruminal pH (mean = 5.7), efficiency of N utilization, and diurnal ingestive behavior were not affected (P>0.05) by protein sources. Protein sources also did not affect the grain-use efficiency (P>0.05), with an average value of 96.6% and only 3.4% of the corn grains recovered in the feces. The concentration of GGT enzyme was greatest (P<0.05) for CM and DDGS. The inclusion of DDG increased the DMI but did not improve the nutrients’ digestibility or N metabolism. The results suggest that 50% of the [1]soybean meal can be replaced by sunflower meal, DDG, and DDGS without affecting the nutritional and metabolic parameters of Nellore cattle fed whole flint corn grain diets, providing opportunities for reducing costs in feedlot systems.