Assessment of a 50:50 mixture of two Bacillus subtilis strains as growth promoters for finishing pigs: productivity improvement and noxious gas reduction.

In this study, we aimed to assess the potential of a 50:50 mixture of two Bacillus subtilis strains in improving the productivity and health of finishing pigs and reducing noxious gases in their feces. These strains were found to abundantly secrete surfactin which has been shown to alleviate the effects of lipopolysaccharides in vitro. For the 10-wk experiment, 200 finishing pigs ([Landrace × Yorkshire] × Duroc) with an average body weight of 54.15 ± 1.70 kg were divided into four groups. Each group was fed with a basal diet supplemented with an equal amount of spores from the two B. subtilis strains at different levels: control group, no addition; treatment group 1, 0.5 × 109; treatment group 2, 1.0 × 109; treatment group 3, 1.5 × 109 cfu·kg-1 addition. During the 10-wk feeding period, dietary supplementation of 0.5 × 109, 1.0 × 109, and 1.5 × 109 cfu·kg-1 of the spore cells from these two strains resulted in a 0.9%, 1.9%, and 2.5% increase in body weight, respectively (linear P < 0.095). During the final 5 wk, the average daily gain (ADG) in weight was increased by the strains at amounts of 0.5 × 109, 1.0 × 109, and 1.5 × 109 cfu·kg-1 with a clear dosage effect (linear P < 0.05). However, neither the gain-to-feed ratio, the average daily feed intake, nor nutrient digestibility was affected by the supplementation. In blood, the endotoxin lipopolysaccharides, and two liver toxicity indicator enzymes; aspartate aminotransferase and lactate dehydrogenase were decreased (P < 0.05) in the 1.0 × 109 cfu·kg-1 spores-feeding group. Furthermore, four noxious gases were reduced by 8 to 20% in feces excreted by pigs fed with 1.5 × 109 cfu·kg-1 spores with a linear dosage effect (linear P < 0.001 to 0.05) during the final 5 wk. Our findings suggest that the mixture of B. subtilis strains may enhance the productivity of finishing pigs by reducing the risk of mild endotoxemia, rather than increasing digestibility or daily feed intake. Therefore, these Bacillus strains have the potential to act as growth promoters for pigs, leading to improved animal health and productivity. These results have significant implications for pig farmers seeking to optimize the health and growth of their animals.