Lactation performance and diet digestibility of dairy cows in response to the supplementation of Bacillus subtilis spores

Bacillus subtilis is a transitory microorganism of the digestive tract, non-pathogenic to animals, and capable of forming spores that are resistant to heat and cold. As an animal feed probiotic the microorganism is supposedly capable of increasing diet digestibility and immunity. Two experiments were conducted to evaluate the effect of Bacillus subtilis spores on milk yield and composition and diet digestibility. In both experiments lactating dairy cows were fed in tie stalls and treatments were force-fed once per day. In experiment 1, 18 Holsteins in late lactation (246±75 days in milk) received a sequence of the treatments Bacillus subtilis strain C-3102 (3.0×109 colony-forming units of spores per day) or Placebo in a crossover design with 39-day periods, a 10-day wash-out between periods, and response evaluated after the 28th day of the periods. The supplementation of Bacillus subtilis spores did not elicit detectable changes in intake (18.3 kg/d, P=0.91), milk (25.3 kg/d, P=0.66) and solids yield and concentration, total tract nutrient digestibility, and chewing activity. In experiment 2, 30 cows (161±72 days in milk) with high milk somatic cell count (725,000 cells/mL) received the same treatments for 16 weeks, in a covariate adjusted randomized block design with repeated measures over time. Bacillus subtilis spores increased the yields of milk (25.3 vs. 23.6 kg/d, P=0.02), protein (0.816 vs. 0.763 kg/d, P=0.01), total solids (2.718 vs. 2.566 kg/d, P=0.05), and energy (60.7 versus 56.5 MJ/d, P=0.02) and milk urea-N tended to be reduced (19.3 vs. 20.8 mg/dL, P=0.06). Milk somatic cell count did not differ between treatments. The positive lactation response to Bacillus subtilis spores supplementation occurred when the probiotic was fed for 16 weeks and there was no evidence to suggest that increased diet digestibility was a mediator of the response.