Effects of supplementing Bacillus subtilis PB6 on health outcomes, Salmonella spp. prevalence, growth performance, and carcass characteristics in finishing beef cattle

Abstract

Objective

We evaluated the effects of supplementation with Bacillus subtilis PB6 on health outcomes, growth performance, fecal Salmonella prevalence, and carcass characteristics in finishing beef steers supplemented the first 60 d or the entire 224 d of the feeding period with B. subtilis PB6.

Materials and Methods

Crossbred beef steers (n = 3,150; arrival BW 274 ± 30.6 kg) were used in a randomized complete block design consisting of 3 dietary treatments (n = 15 blocks per treatment). Treatments included the following: (1) a control diet contained no B. subtilis PB6 (CON); (2) a diet that included CLOSTAT supplemented with 0.5 g/steer daily of B. subtilis PB6 (CLOSTAT 500, Kemin Industries Inc.) to provide 6.6 × 10⁹ cfu/g active ingredient for the entire duration of the feeding period (CLO); or (3) a diet that included B. subtilis PB6 at a dose of 0.5 g/steer daily the initial 60 d of the feeding period (CLO60). Based on established criteria, metaphylaxis was administered after arrival to 7 blocks (21 pens) to prevent bovine respiratory disease. Fresh fecal matter was collected aseptically from multiple locations (n = 10 locations within each pen), and lymph nodes were obtained at slaughter from a subset of carcasses within each lot (n = 12) to determine Salmonella prevalence.

Results and Discussion

No interactions were observed between treatment and metaphylaxis throughout the study. The percentage of respiratory deaths was greater for steers in CLO60 than CLO and CON from d 0 to 60, but there were no growth performance differences noted among treatments. Likewise, there were no differences in lymph node prevalence of Salmonella among treatments; however, there was a decrease in fecal Salmonella prevalence for CON versus CLO and CLO60 steers from d 45 to 90.

Implications and Applications

Supplementation of B. subtilis PB6 for the first 60 d or the entire feeding period had no effect on health outcomes, growth performance, and carcass characteristics. Moreover, feeding B. subtilis PB6 for the first 60 d or entire feeding period did not affect Salmonella prevalence in the subiliac lymph nodes.