Abstract
The goal of this study was to compare the effects of Bacillus subtilis and the antibiotic enrofloxacin on growth performance, immune response, intestinal histomorphometry and cecal Salmonella numbers in broilers challenged with S. gallinarum. Salmonella-free chicks (n = 240) were allocated to four groups, comprising six replicates (n = 10) each. Group NN was not infected and received no treatment. Group SN was infected with Salmonella and received no treatment. Group SE was infected with Salmonella and treated with the antibiotic enrofloxacin. Group SP was infected with Salmonella and treated orally with the probiotic B. subtilis. Initially the groups that were infected with Salmonella had reduced growth performance compared with NN. By the fourth week, SE and SP had recovered and weighed as much as or more than NN. The SP group had greater cellular immunity and relative weights of the bursa and thymus than the other groups. SN had the lowest villus height in all the segments of the small intestine and a larger Salmonella population in the ceca. Probiotic supplementation reduced the pathological outcomes more than enrofloxacin. Prophylactic use of B. subtilis-type probiotics had similar effects to the use of antibiotics, alleviated the stress related to infection of S. gallinarum, and improved the growth performance, immune function, and gut mucosal development in broilers.
 Keywords: growth promoters, immunity, probiotics, poultry villi length
Highlights
Salmonellosis is one of the leading causes of lost productivity in poultry (Saleem et al, 2016) and a major source of bacterial food poisoning in humans
Probiotics play an important role In combatting its invasion, and improve growth performance, but protect the mucosal epithelium from bacterial invasion, and impede its growth in tissues
The probiotic B. subtilis, which is added as a feed supplement, is gaining popularity in poultry production across the world by boosting the immune response (Dersjant-Li et al, 2014)
Summary
Salmonellosis is one of the leading causes of lost productivity in poultry (Saleem et al, 2016) and a major source of bacterial food poisoning in humans. The European Union (EU) withdrew the use of antibiotics in food animals to circumvent the emergence of resistant pathogenic organisms and their transmission to humans through the consumption of contaminated food (Dersjant-Li et al, 2014). This prohibition led to a decline in animal performance from bacterial stress and reduced growth. B. subtilis produces antimicrobial substances and is assumed to facilitate gut health (Sikandar et al, 2017; Abudabos et al, 2019) It favours the growth of lactic acid, producing bacteria and other beneficial microorganisms in the gut that act to competitively exclude pathogens (Yang et al, 2018). There is a shortage of information about the protective effect of B. subtilis (QST-713) on the gut histology of and other
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