Effect of ground soybean and starch on intake, digestibility, performance, and methane production of Nellore bulls

Abstract

It was hypothesized that replacement of corn with soybean hulls as the energy source, combined with ground soybean as the lipid source, would reduce methane emissions from feedlot animals without affecting their performance. This study aimed to evaluate the effects of including ground soybean combined with either a high or a low level of starch on intake, digestibility, performance, and methane emission of young Nellore bulls (n = 28, initial weight = 395 ± 32 kg) in the feedlot during the finishing phase. Diet treatments consisted of high (HS; approx. 250 g/kg) or low (LS; approx. 110 g/kg) starch levels, with (WSB) or without (NSB) soybean. Ground soybean was added as a lipid source to diets HS-WSB, LS-WSB, HS-NSB, and LS-NSB, representing 58.7, 64.6, 24.8, and 31.4 g/kg ether extract in the total dry matter, respectively. Animals were distributed in a completely randomized design, in a 2 × 2 factorial arrangement. After 119 days, the animals were slaughtered. Animals fed soybean demonstrated an average reduction of 11% in their intakes of dry matter, organic matter, and crude protein (P = 0.01). There was a significant effect of the association between starch and soybean on neutral detergent fiber intake (P = 0.01). Diets containing soybean affected the digestibility of the animals, reducing the apparent digestibility of dry matter by 3% (P = 0.02) and the digestibility of organic matter by 2.8% (P = 0.03). A significant interaction was detected between starch and soybean on the apparent digestibility of ether extract (P = 0.02) and neutral detergent fiber (P = 0.04); the lowest values for ether extract (750 g/kg) and neutral detergent fiber (432 g/kg) were obtained with HS-WSB. The animals that received WSB had their feed efficiency increased by 17% (P = 0.01). The enteric CH4 emissions of the animals fed WSB reduced significantly (P = 0.01), with 28% decrease in g CH4/d and g CH4/y, 16% decrease in g CH4 per kg of dry matter intake, and 23% decrease in CH4 losses per percent of gross energy intake. The inclusion of approximately 250 g/kg of soybean in the diet of young Nellore bulls in the feedlot provides an increase in their feed efficiency and reduces their enteric methane emission, regardless of the level of starch in the concentrate.