# 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

## TL;DR

This study found that adding autolyzed yeast to lamb feed improved growth and energy use, but adding a probiotic bacteria did not enhance these benefits.

## Contribution

Demonstrates that combining a prebiotic and probiotic in lamb diets does not synergistically improve growth or carcass traits beyond the prebiotic alone.

## Key findings

- Lambs supplemented with autolyzed yeast (SC) showed improved growth rate, gain efficiency, and dietary energy utilization.
- Combining SC with Bacillus subtilis (BS) did not enhance these improvements compared to SC alone.
- Probiotic BS supplementation alone had no significant effect on lamb growth or carcass traits.

## Abstract

Due to their specific properties, the prebiotic autolyzed yeast Saccharomyces cerevisiae (SC) and the probiotic bacterium Bacillus subtilis (BS) can theoretically exhibit a synergistic effect when combined and offered in ruminant diets. Thus, the aim of this experiment was to evaluate the combination of both as feed additives on feed utilization efficiency and carcass traits in fattening lambs. For that, SC and BS were offered alone or in combination for 83 days, and one group served as the control (non-additive supplementation). Lambs that received SC showed improvements of 12% in growth rate, 6.1% in gain efficiency, and 5.5% in observed-to-expected dietary energy utilization, without altering carcass traits or composition. Contrary to our expectations, combining autolyzed SC with BS did not enhance those responses when compared to autolyzed SC alone. On the other hand, lambs that received BS supplementation alone did not show any improvements when compared to non-supplemented lambs.

Due to their specific properties, the autolyzed yeast Saccharomyces cerevisiae (SC) and bacterial Bacillus subtilis (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, p = 0.41), average daily gain (ADG, p = 0.64), carcass traits (p ≥ 0.08), tissue composition (p ≥ 0.32), and relative visceral organ mass (g/kg EBW, p ≥ 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%, p = 0.03), gain efficiency (6.1%, p = 0.04) and observed-to expected dietary energy efficiency (5.5%, p = 0.04). Supplemental SC and SC + BS increased hot carcass weight (p = 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.