Influence of Dietary Bacillus subtilis C-3102 Spores on Live Performance of Broiler Chickens in Four Controlled Pen Trials

Four trials were conducted to evaluate Bacillus subtilis spores as a direct-fed microbial for improving broiler performance. In trials 1 to 3, straight-run Cobb 500 broiler chicks were grown to 42, 42, and 39 d, respectively, to evaluate diets containing Calsporin (0.05%; contributing spores at 0.003% level), an alternative growth promoter, compared with control basal diets. The additive significantly increased BW in all experiments (average +0.113 lb or +2.90%) and decreased feed conversion ratio in 2/3 trials (average 3 trials −0.027 lb of feed/lb of body weight or −1.46%) without affecting mortality. In trial 4, on new litter with a used litter covering and relatively high stocking density (0.67 ft²/bird or 0.0622 m²/bird), Ross × Hubbard HiY equal mixed-sex chicks were grown to 49 d of age. On all sides of pens, 34 in. high corrugated paper was used to prevent crossover of test additive but provided minimal ventilation and caused wet litter. Chick quality was substandard due to omphalitis. Bacillus subtilis spores (0.003%) treatment gave best BW and feed conversion results (+0.446 lb or +8.66% and −0.146 lb of feed/lb of body weight or −6.92%) compared with control treatment though not significantly better than bacitracin-methylene disalicylate (BMD) (55 ppm) or Bacillus subtilis spores plus BMD. Mortality was significantly lowerin control than the combined additive treatment (in which no culling and large differences in growth increased mortality of weaker chickens). Bacillus subtilis spores improved broiler chicken BW and feed conversion ratio and in a direct comparison successfully replaced BMD.