Is the Probiotic Efficacy of Bacillus Amyloliquefaciens Strain H57 Dose Dependent?

The effect of probiotics on animal performance is not consistent and may be impacted by multiple factors, such as dose, route of administration, disease stress, and management. We have previously examined the efficacy of the probiotic Bacillus amyloliquefaciens strain H57 (H57) in a disease stress model with subclinical necrotic enteritis (NE) (Shini et al., 2020); in the study only one dose of H57 (10⁸ CFU/g feed) was used. The purpose of present study was to evaluate if the effect of H57 on performance and gut health of broiler chicks challenged with subclinical NE is dose dependent.

Day-old, male, Ross 308 broiler chicks were assigned to 48 cages by stratified randomization with 10 chicks per cage in an environmentally controlled room. Day-old chicks were fed a wheat/soybean basal diet that was also supplemented with graded doses of H57 at 0, 10⁶ , 10⁷ , and 10⁸ CFU/g feed, respectively; Treatments 1, 2, 3 and 4. Treatments 5-8 replicated Treatments 1-4, but were challenged by NE. Each treatment diet was fed to 6 cages and the procedure to induce NE, as detailed by Shini et al. (2020) was followed. Briefly, at 9- days of age, the birds were challenged with Eimeria spp. vaccine with 20 times the manufacturer’s recommended dose by drinking water. At 14-days of age, Clostridium perfringens inoculated broth was mixed into the diets.

Body weight and feed intake were recorded weekly. The experiment ended on day 21 when samples were collected from two birds per replicate, including liver, spleen, bursa of Fabricius, pooled ileal digesta, and ileal tissue for histomorphology. The birds were also visually scored for NE gut lesions and the following day, the NE gut lesions of the remaining birds were scored. Body weight was not significantly different (P> 0.05) between birds fed graded levels of H57 (Treatments1-4). However, the body weight of NE-birds treated with H57 at 10⁷ CFU/g was the highest (P < 0.05) compared with other challenge groups. H57 improved the FCR of both non-challenged and challenged birds. Challenged birdsfed H57 at 10⁸ CFU/g had a similar FCR to the control group. The ratio of villi height and crypt depth of NE-birds supplied with 10⁷ CFU/g H57 was significantly (P < 0.05) lower than NE-only birds. NE-birds supplied with H57 at 10⁸ CFU/g had the lowest gut lesion score amongst challenged groups and were not significantly different to the non-challenged groups. Digesta pH of challenged groups was significantly (P < 0.05) lower than the non-challenged groups. NE challenged birds did not have a significantly different (P > 0.05) digesta pH compared with non-NE birds when fed H57 at 10⁷ CFU/g and 10⁸ CFU/g.

The data showed that there was a dose effect with dietary addition of H57 with respect to the parameters measured. However, birds receiving the highest dose (10⁸ CFU/g) did not always outperform the birds receiving 10⁷ CFU/g feed. It was demonstrated that H57 reduced enteric disease stress, maintained gut health and integrity, and growth performance.

ACKNOWLEDGEMENT: This study was supported by an Advanced Queensland Industry Partnership Grant.