The effects of Bacillus subtilis, dietary calcium and coccidial vaccines in broilers experiencing naturally occurring necrotic enteritis

Necrotic enteritis (NE) is a disease that negatively affects broiler performance and has increasingly become a problem with the reduced use of antibiotics. There is increased interest to utilize alternative methods including coccidial vaccines and direct fed microbials (DFM) to reduce or prevent NE. Additionally, it has been demonstrated that reduced dietary Ca can reduce NE mortality. The objective of the first study was to examine the effects of Bacillus subtilis (DFM) in combination with attenuated (AV) and non-attenuated (NV) coccidial vaccines in broilers with NE. The objective of the second study was to determine the effects of DFM, antibiotic (BMD) or negative control (NC) with standard dietary Ca (0.9%) or below standard Ca (0.75%, 0.6%) in broilers with NE. To induce a natural NE occurrence, birds were vaccinated with the appropriate coccidial vaccine and then placed on reused litter from a previous flock exhibiting NE lesions and mortality. In the first trial DFM reduced BW and BW gain (P ≤ 0.05) during the starter phase (0 to 14 d). The addition of a DFM in the AV group resulted in decreased (P ≤ 0.05) BW gain and BW at 42 d. The DFM in the NV group resulted in improved (P ≤ 0.05) mortality corrected feed conversion ratio from 0 to 42 d. Overall, with a natural NE occurrence, the effect of DFM was variable depending on what type of coccidial preventative was utilized and was beneficial when used with NV. In the second trial BW and BW gain were increased in broilers fed 0.60% dietary Ca and DFM compared to 0.90% Ca and NC (P ≤ 0.05). Broilers fed 0.60% Ca had reduced NE mortality compared to broilers fed 0.90% Ca (P ≤ 0.05). Reducing dietary Ca to below industry standards was able to lessen the severity of NE though the addition of DFM was needed to improve BW. Overall, with a natural NE occurrence, the DFM was beneficial when used with NV and in diets with 0.6% dietary Ca.