The effects of Bacillus subtilis spores and yeast cell wall supplementation on growth and health in Holstein dairy calves

The study aimed to assess the impact of Bacillus subtilis spores and yeast cell wall (YCW) on the performance and health of dairy calves during the milk-feeding period. Thirty female Holstein calves (birth body weight [BW] of 36.7 ± 4.81 kg) were randomly assigned to three treatments: Control (CTL, no additives), T1 (Bacillus subtilis spores), and T2 (Bacillus subtilis + YCW). Animals were individually housed with free access to water and commercial pellet starter. Calves received 8 L/d of pasteurized waste milk and were weaned at 63 d of age. The treatments (T1 and T2) were mixed into milk and administered daily from 3 to 63 d of age. Dry matter (DM) intake (from liquid and starter feed), fecal score, and rectal temperature were recorded daily. Additionally, heart girth was measured at 0, 15, 30, 45, and 60 d of age, and BW was measured at 0 and 60 d of age. Blood was sampled from the jugular vein at 0, 20, and 60 d of age for analysis of serum immunoglobulin G (IgG). There was treatment × time interaction (P = 0.04) for fecal consistency scores. Calves supplemented with Bacillus subtilis tended (χ2 test, P = 0.07) to have lower cases of diarrhea than other groups. T1 or T2 supplementations did not affect milk DM intake, starter DM intake, or total DM intake. Growth performance (BW at weaning and average daily gain) was similar between treatments. Dairy calves fed Bacillus subtilis plus YCW tended to have (P = 0.09) higher rectal temperature and had higher frequency (χ2 test, P < 0.01) of rectal temperature >39.1°C compared to the CTL and Bacillus subtilis groups. However, treatments had similar levels of serum IgG (CTL = 18.3, T1 = 16.7, and T2 = 18.6 mg/mL; P = 0.58). Our results suggest that Bacillus subtills and YCW may interact in the digestive tract of young calves as evidenced by the increased rectal temperature in T2. While the cause of this interaction remains uncertain, there was no negative effect on the animal health or growth performance. The use of Bacillus subtilis spores shows promise in improving fecal consistency scoring in dairy calves fed pasteurized waste milk during the pre-weaning phase.