Bacillus spp. supplementation stimulates the growth of preweaning bull calves offered milk replacer and pelleted starter supplement

Objective

In 2 experiments, the objective was to evaluate the effects of supplementing a Bacillus-based direct-fed microbial (DFM) on growth rates of preweaning dairy bull calves.

Materials and Methods

In experiment (Exp.) 1, 62 Holstein-Friesian bull calves were ranked by initial BW and assigned to (1) no DFM supplementation (n = 31; CON) or (2) supplementation of a Bacillus-based DFM in the milk replacer and pelleted feed (n = 31; DFM). Throughout the study, calves were housed individually, milk replacer was offered twice daily with equal amounts being offered twice daily following a programmed feeding. Starting on wk 3 of the study, pelleted feed was offered in controlled amounts to all calves, whereas corn silage and lucerne hay were offered ad libitum. In Exp. 2, 52 Holstein-Friesian bull calves were assigned to the same treatments as reported in Exp. 1 and maintained in group pens, with individual milk and solid feed intake recordings. All data were analyzed with the MIXED procedure of SAS (version 9.4), using calf as the experimental unit.

Results and Discussion

In Exp. 1, DFM-fed bull calves were heavier versus CON on d 42 and 63 of the study. A similar treatment × day interaction tended to be observed for ADG, so that ADG was greater in DFM from d 21 to 42 and tended to be greater from d 0 to 63. Similarly, in Exp. 2, calves fed DFM were heavier on d 56 (treatment × day interaction). For ADG, DFM-fed bull calves had a greater ADG from d 28 to 56 and 0 to 56. Daily pellet intake and G:F for calves fed milk replacer were greater for DFM-fed calves.

Implications and Applications

In summary, feeding a Bacillus-based DFM improved growth rates of low-risk, preweaning Holstein-Friesian bull calves, while also positively affecting milk and solid feed intake. These results indicate that bacterial-based DFM are a feasible strategy to promote the growth rate of calves offered milk replacer preparations.