Impact of replacing soybean meal in beef cattle diets with inactive dry yeast, a sugarcane by-product of ethanol distilleries and sugar mills

This study assessed the intake, total and partial apparent digestibility of nutrients, pH, ruminal ammonia concentration, nitrogen efficiency usage, and productive performance of beef cattle fed with different soybean meal replacement levels with inactive dry yeast (IDY 0, 250, 500, 750, and 1000 g/kg). The forage:concentrate ratio was 60:40 and the forage source was corn silage. Concentrates were formulated to comprise 220.0 g/kg CP independent of treatments. In the first experiment (EXP 1), 35 Nelore bulls with an initial average weight of 370 ± 42 kg were distributed across a completely randomized design, with five treatments and seven replicates to assess nutrient intake and performance. EXP 1 lasted 98 days and was divided into a 14-day adaptation period and three experimental periods of 28 days each. In the second experiment (EXP 2), five castrated Nelore steers with an initial average weight of 320 ± 39 kg were fistulated in the rumen and abomasum and distributed in a 5 × 5 Latin square design, balanced for residual effect. The purpose of this experiment was to assess the total and partial digestibility of nutrients, pH, ruminal ammonia nitrogen, and nitrogen efficiency of usage. EXP 2 lasted 90 days, divided into five experimental periods. Each period lasted 18 days and was divided into 10 days for adaptation to the diets and 8 days to collect samples. The intake of dry matter (DMI) decreased linearly (P = 0.03) with increased dietary IDY levels. Conversely, the intake of neutral detergent fiber assayed with a heat-stable amylase and corrected for ash and nitrogenous compounds [aNDFom(n)] in g/day (P = 0.043), and the g/kg body weight (P = 0.011) increased linearly as IDY was added to the concentrate. The experimental diets showed no effect (P > 0.05) on the total and partial apparent nutrient digestibility. IDY had no effect (P > 0.05) on ruminal pH, ruminal ammonia nitrogen, or dietary nitrogen efficiency. Additionally, IDY had no effect on productive performance variables, with the exception of average daily gain (ADG), which decreased linearly (P = 0.028) as IDY was added to the concentrate. IDY addition resulted in decreases in DMI and ADG for beef cattle in feedlots (EXP 2). However, the apparent digestibility of nutrients and microbial efficiency were not affected. In addition, IDY did not reduce feed conversion or carcass gain. The high market price of soybean meal might make feasible its total replacement by IDY, even considering the possibility of a small reduction in ADG.