Effect of a Bacillus-Based Probiotic on Performance and Nutrient Digestibility When Substituting Soybean Meal with Rapeseed Meal in Grower–Finisher Diets

SIMPLE SUMMARY: The objective of this study was to test the hypothesis that B. subtilis and B. licheniformis supplementation in a negative control diet (in comparison to a standard control diet) has the potential to improve performance and nutrient digestibility of growing–finishing pigs. Three fattening pig groups were used: standard diet, negative control diet (5% soybean meal replaced by 5% rapeseed meal), or the negative control diet supplemented with a probiotic. The use of a probiotic preparation containing specific Bacillus strains as a feed additive for growing–finishing pigs resulted in improved growth performance and faecal digestibility, and was able to counteract the lower nutritional level of a negative control diet. ABSTRACT: The objective of the present study was to test the hypothesis of B. subtilis and B. licheniformis supplementation to a negative control diet in comparison to a standard control diet, had the potential to improve the performance and nutrient digestibility of growing–finishing pigs. For this purpose, 384 fattening pigs of 85 d of age were allotted to three treatments: a standard diet, a negative control (NC) diet (5% soybean meal replaced by 5% rapeseed meal), or a NC diet + probiotic. After reaching a body weight of approximately 110 kg, all animals going to the slaughterhouse (87% of total pigs) were selected to measure carcass quality. Moreover, the apparent total tract digestibility of protein was evaluated at the end of the grower period. The results of this study indicate that supplementation of the tested Bacillus-based probiotic significantly improved average daily gain (ADG, +14.6%) and Feed:gain ratio (F:G, −9.9%) during the grower phase compared to the NC diet. The improvement observed during the grower phase was maintained for the whole fattening period (ADG, +3.9%). Probiotic supplementation significantly improved the total apparent faecal digestibility of dry matter and crude protein in pigs at the end of the grower period. The improvements observed with the additive tested could indicate that supplementation of the Bacillus-based probiotic was able to counteract the lower level of crude protein and standardised ileal digestible amino acids in the NC diet by means of improved protein digestibility.