Replacing soybean meal with liquid yeast in the diet of feedlot lambs: nutritional and metabolic traits

Liquid yeast is a by-product of the sugar and alcohol industry with potential for use in ruminant diets. However, there are doubts as to how much should be included in the diet of lambs in the finishing phase. The aim of this study was to evaluate the effects of replacing soybean meal with liquid yeast in the diet of lambs in confinement on consumption, nutrient digestibility, rumen and blood parameters, microbial protein synthesis and the animals' ingestive behavior. Five experimental diets with 0, 25, 50, 75 and 100% replacement of soybean meal by liquid yeast in the dry matter were evaluated. Ten uncastrated male Santa Inês x Dorper crossbred lambs were used, with an average weight of 22.6 ± 5 kg and an average age of 4 months. The animals were randomly allocated to a double and simultaneous Latin square design (5×5). The study lasted 105 days, with each experimental period lasting 21 days and an adaptation period of 15 days. The inclusion of liquid yeast in the lambs' diet changed their intake of dry matter and nutrients.The variables fitted a quadratic regression model, with maximum points observed for DM (14.02%), OM (15.78%), MM (10.00%), CP (16.50%), NDF (15.87%), FDA (11.73%), CpNDF (11.62%), total carbohydrates (14.28%), NFC (12.29%) and NDT (13.92%). Digestibility (g/kg) was significantly influenced (p < 0.05) by the levels of DM, OM, CP, NDF and total carbohydrates, showing a linear behavior, while NFC showed a quadratic adjustment, with a maximum point at 6.71%. The parameters of purines absorbed and microbial proteins showed a significant increasing linear effect (p < 0.05), while the parameters of plasma urea, nitrogen ingested, nitrogen in the feces, nitrogen retained, nitrogen absorbed and nitrogen balance showed a significant decreasing linear effect (p < 0.05). Replacing soybean meal with liquid yeast from the sugar-alcohol industry in lamb diets can be done safely up to a level of 50%, based on dry matter intake, digestibility and rumen parameters.