Efficacy of the Probiotic Bacillus Amyloliquefaciens H57 in a Chick Subclinical Necrotic Enteritis Model

Probiotics are showing promise as antibiotic replacements but more scientific evidence is required to validate their beneficial effects. Previous broiler feed trials conducted with Bacillus amyloliquefaciens strain H57 (H57) indicated variable bird performance (Bajagai, 2018). In these trials, birds were kept under “optimal” experimental conditions, where most of stressors were absent from the environment. There is some evidence that probiotics are best applied when a bird or animal is under stress, from infectious, nutritional or environmental stressors, and in commercial chickens, enteric infections are one of the most important environmental challenges in early life. Necrotic enteritis (NE), caused by Clostridiumperfringens (CP), has become one of the most significant diseases in broilers. Subclinical NE, which is difficult to diagnose, can spread through flocks, resulting in substantial production losses. A subclinical NE model was developed in broilers to assess the efficacy of H57 in improving intestinal health and preventing NE. It was our hypothesis that, H57 spores administered in the diet during the first three weeks of life, will maintain intestinal health and improve feed utilisation.

Subclinical NE was induced in Ross broilers by exposing them to a high dose of Eimeria spp. vaccine (20x the manufacturer's recommended dose) via drinking water on day 9 post-hatch, and 5 days later to CP culture (strain EHE-NE18, CSIRO) mixed in the feed. In this factorial study there were six treatments (control, Eimeria-challenged, CP-challenged, NE-challenged, NE-H57, H57) each with six replicates of eight chicks. The control diet was supplemented with the probiotic (2x10⁸ spores/g feed) throughout the study, and fed to two groups of birds, NE-H57 and H57. Data on performance, pasty vent, NE lesion scoring, and histopathology were used to assess effects of H57 on bird gut health.

There were no significant treatment effects on total body weight and feed intake. However, in NE-H57 birds, FCR was significantly improved when compared to NE birds (1.28 vs. 1.36; P < 0.001). In H57 birds, FCR was improved by 0.03 units when compared to controls (1.24 vs. 1.27; P = 0.051). NE birds had a higher occurrence of pasty vent, than Eimeria, CP or NE-H57 birds (41%, vs. 27%, 29%, 19%; P < 0.001). Lesion scores of NE birds were also higher (P < 0.001) than in challenged (Eimeria, CP, and NE-H57), and unchallenged birds (control and H57), 5.67 vs. 2.56, 2.78, 2.10, 1.17, 0.83, respectively). There was a strong correlation between pasty vent and lesion scores (Pearson’s r = 0.56; P < 0.001). Microscopic evaluation of ileal mucosa showed mucosal damage and necrosis in NE birds. In contrast, villi from NE-H57 birds were normal in appearance, with no damage or infiltration with Eimeria or CP. It was concluded that H57 is more effective in birds subjected to an infectious challenge. NE-H57 birds had improved feed efficiency and maintained epithelial barrier integrity. This was confirmed with electron microscopy as described by Shini et al. (2020).

ACKNOWLEDGMENT: Funding was provided by an Advance Queensland Industry Partnership grant.