Can the supplementation of autolyzed yeast (Saccharomyces cerevisiae) affect the diet digestibility, feeding behavior, levels of blood metabolites, and performance of Dorper × Santa Ines lambs finished in feedlot?

This study aimed to evaluate the effect of autolyzed yeast (obtained from culture of Saccharomyces cerevisiae in sugarcane derivatives) supplementation on diet digestibility, feeding behavior, levels of blood metabolites associated with protein and energy metabolism, and performance of Dorper × Santa Ines lambs finished in feedlot. Twenty-four non-castrated male lambs with an average age of 4 months and a body weight (BW) of 19.49 ± 3.08 kg were allocated to individual pens within a covered and elevated shed. The pens had a slatted floor without bedding suspended 1.8 m above the ground, and an area of 1.5 m. The trial was set out in a completely randomized design with two treatments and twelve replicates each. The treatments consisted of a basal diet without yeast products (Control) or with yeast culture (Yeast, RumenYeast® at 5 g/animal/day). Lambs were fed ad libitum with a total mixed ration (TMR) composed of 400 g/kg of dry matter (DM) of Tifton 85 hay (Cynodon spp.) and 600 g/kg DM of concentrate feed, and contained 146 g/kg DM of crude protein and 2.30 Mcal/kg DM of metabolizable energy. The experiment was conducted over 84 days, with the first 14 days serving as an adaptation period. The subsequent experimental period was divided into two phases to evaluate animal performance (Days 1-63) and DM digestibility (Days 64-70). The supplementation with autolyzed yeast did not affect rumen or fecal pH, the DM digestibility, as well as the feeding behavior of lambs (the time spent on feeding, rumination, water intake, and idleness activities). In addition, yeast supplementation did not alter the serum levels of albumin, creatinine, urea, or level of plasma glucose, resulting in similar animal performance compared to the Control group. The mean values for final BW, DM intake, average daily gain, and feed conversion ratio were 37.52 kg, 1.051 kg/day, 0.286 kg/day, and 3.74 kg DM/kg gain, respectively. In the conditions of this study, the supplementation of autolyzed yeast in TMR (5 g/animal/day) does not affect diet digestibility, feeding behavior, blood metabolites, or performance of lambs finished in feedlot. Regarding that metabolic and performance lamb responses were not improved, the supplementation of autolyzed yeast at the tested dose is not recommended. However, it is important to note that markers related to immunity and inflammation were not evaluated in our work, and these should be considered in future studies.