Weaning is a worrying period in the life cycle of pigs, which is associated with changes in diet, gut environment and gut morphology, and thus may result in low growth percentage, high diarrhoea incidence and imbalanced intestinal microecology [16]. The weaning period is a critical time in whole piglet’s life, because the young pigs are separated by the sow, resulting in an abrupt change in diet, a move to a new environment and mixing with unfamiliar animals, generally younger [17, 18]. All raw materials used in the diet must to be safe and suitable for their utilization in animal nutrition. Generally, raw materials are recognized as safe (GRAS) or otherwise deemed acceptable for use in feed [18]. The composition of feedstuff and feeding management are critical issues that influence the health state of piglets after weaning [19]. The animal feed can be exposed to numerous factors (biological, chemical, physical and other agents), which can affect the animal status health and, indirectly, human [18]. Previous studies with supplementation of Bacillus-based probiotic had a significant effect on ADG and ADFI of weaned piglets, reducing the F: G [19, 20].
In our study, soybean meal was included 13% (w/w) as main protein resource for animal production [21] and the addition of Bacillus subtilis can ferment it, as affirmed Kiers et al. [24], due to the hydrolysis of protein to amino acids and peptides [22]. Bacillus subtilis strain concentration is in concordance with EFSA Guide,,Panel on Additives and products or substances used in Animal Feed” which affirms that the minimum inclusion level in piglets feeding stuffs is 1 x 109 CFU/kg feed [23].
The effect of a probiotic could be affected by strain composition and inclusion levels, but rendering to the results of previous reports, it should be noted that the positive effects of probiotics on growth performance were always observed in the early period after weaning [24].
The dramatic fluctuations in GIT after weaning and the gut needs time to adapt to the new feed, may cause a gastrointestinal infection, mostly colibacillosis diarrhoea, which producing an extensive morbidity and/or mortality (around 17% of piglets born in Europe) in the most serious of affected cases [25].
Bacillus spp. is not a principal member of the normal animal microbiota and could not colonize the intestine for long periods; it consumes oxygen rapidly and reduces the pH value, which this parameter favors Lactobacilli number and inhibits pathogens like E. coli and Salmonella spp. [27]. As a Gram-positive bacterium and the ability to form endospores, Bacillus subtilis can endure the high temperatures of animal feed pelleting and also, to be stable for long time storage [26].
Post-weaning diarrhoea (PWD) is a condition in weaned piglets characterized by the frequent ejection of soggy faces during the first 2 weeks after weaning and continues to represent one of the major economic problems for the pig industry worldwide [27]. Several studies with the addition of B. subtilis as DFM products may be a means for GIT health by beneficial bacteria stability, reducing diarrhoea incidence and enhancing the growth performance [28, 29].
The results from previous studies [30, 31] found that Bacillus supplementation reduced the incidence and severity of diarrhoea in weaning piglets.