Evaluation of optimum inclusion levels of as replacement for antibiotic growth promoters in broiler chickens production under field conditions in Nigeria

Abstract

A feeding trial was conducted to evaluate the response of broiler chickens fed diets supplemented with Bacillus subtilis as replacement for antibiotic growth promoters (AGPs). A total of 510 day old Ross broiler chicks were allotted randomly to five dietary treatments each replicated thrice, with 34 chicks per replicate. Bacillus subtilis was included at 0, 75000, 150,000 and 225,000cfu/100 Kg diet for T1-T4, respectively while T5 had Oxytetracycline. Parameters collected were on growth performance, Haematology, liver function, immune response, Antioxidant capacity, villi Morphometrics and ceacum microbial contents. All data were subjected to analysis of variance and significant differences among treatment means were compared using the Turkey test of significance. The results for the starter phase showed birds on the antimicrobials had significantly (P<0.05) high final weight, weight gain, feed intake and better feed conversion ratio than the control. Chicks fed diet supplemented with 225,000 cfu Bacillus subtilis showed high performance in terms of final weight, weight gained, best and least feed cost per kg gain (N 235.2) and feed conversion ratio (1.60). Haematological indices were not significantly (P>0.05) different for the starter phase while significant (P<0.05) differences were observed in MCH (Mean corpuscular haemoglobin) and MCHC (Mean corpuscular haemoglobin Concentration). Liver function indices showed decreased concentration for Aspartate-amino transferase (AST) (33.30-43.30 μL) and Alkaline phosphatase (ALP) (72.30-85.80 μL respectively) for the Bacillus subtilis diets compared to control treatment values of 56.00μL and 85.80μL for AST and ALP respectively. The result for Immune response showed that the level of albumin to globulin ratio increased for birds fed levels of Bacillus subtilis andAGPthan in the control after each administration of Gumboro and Lasota vaccines. Results for Antioxidant capacity showed that therewere no Significant (P>0.05) difference in all parameters measured except for Glutathione peroxidase (GPx).The GPx activity was significantly (P< 0.05) higher for birds fed levels of Bacillus subtilis when compared with the control and AGP. The result for the finisher phase showed that Birds fed diet supplemented with 75,000 cfu showed best performance in terms of final weight, feed consumed, feed conversion and had the least cost of production. VilliMorphometric showed significant (P<0.05) differences in all parameters measured except for villi width. Villi area, height, width, crypt depth and villi height/crypth depth ratio were higher for birds fed levels of Bacillus subtilis and AGP than the control. Levels of Bacillus subtilis in the diet increased beneficial bacteria population and also prevent the colonization of the gut by pathogenic bacteria. It is concluded that Bacillus subtilis significantly improved growth of broiler chickens, feed conversion, significantly lowered cost of production even more than the AGPS; promotes antioxidant capability of birds; enhanced disease resistance by improving the immune response of broiler chickens. Bacillus subtilis is therefore a potential replacement for antibiotic growth promoters.