Effect of Combining a Prebiotic (Autolyzed Yeast from Saccharomyces cerevisiae) and Probiotic (Bacillus subtilis) Added in a High-Energy Diet on Growth Performance, Dietary Energetics, and Carcass Traits of Fattening Hairy Lambs

Due to their specific properties, the autolyzed yeast <i>Saccharomyces cerevisiae</i> (SC) and bacterial <i>Bacillus subtilis</i> (BS) theoretically can have a synergistic effect when combined and offered in ruminant diets. Thus, the aim of this experiment was to evaluate the effect of their combination as feed additives on growth performance, dietary energy, carcass traits, and visceral organ mass in finishing lambs. For this reason, 48 Pelibuey × Katahdin lambs (98 ± 17 d age; initial weight = 20.25 ± 3.37 kg) were used in a feeding trial lasting 83 d. Lambs were blocked by weight and assigned to 24 pens. Treatment consisted in supplementing a high-energy diet with probiotic and/or prebiotic as follows: (1) finishing diet without probiotic or prebiotic supplementation (Control), (2) finishing diet supplemented with 1.5 g SC/kg diet, (3) finishing diet supplemented with 1.5 g BS/kg diet, and (4) finishing diet supplemented with 1.5 g SC plus 1.5 g BS/kg diet. There were no synergistic (interaction) effects by combining SC + BS in any of the variables evaluated. Lambs that were supplemented with BS showed a very similar response on dry matter intake (DMI, <i>p</i> = 0.41), average daily gain (ADG, <i>p</i> = 0.64), carcass traits (<i>p</i> ≥ 0.08), tissue composition (<i>p</i> ≥ 0.32), and relative visceral organ mass (g/kg EBW, <i>p</i> ≥ 0.15) than non-supplemented lambs. Compared to the control group, lambs that received SC alone or in combination with BS showed greater average daily gain (12.0%, <i>p</i> = 0.03), gain efficiency (6.1%, <i>p</i> = 0.04) and observed-to expected dietary energy efficiency (5.5%, <i>p</i> = 0.04). Supplemental SC and SC + BS increased hot carcass weight (<i>p</i> = 0.04) without effects on the rest of the variables evaluated including the shoulder tissue composition whole cuts, and visceral organ mass. It was concluded that SC improves growth performance and dietary energy in finishing lambs without changes in carcass traits or carcass composition. Combining SC with BS did not improve the magnitude of the response of SC supplemented alone. In this study, the inclusion of a 1.5 g/kg diet of BS during a long-term period (83 d) did not show benefits to finishing lambs.