Effects of feeding a Bacillus-based direct-fed microbial during a 60-day receiving program on performance and...

The objective was to evaluate the effects of Bacillus-based DFM supplementation during a 60-day feedlot receiving phase. Eighty-four Angus calves were ranked by initial body weight (BW = 280 ± 7.4 kg), age (233 ± 6 days), and sex (38 heifers and 46 steers), and allocated to 20 pens in a completely randomized design. Pens were randomly assigned to receive (i) a total mixed ration (TMR) plus 165 g of protein-mineral supplement + 3 g of a Bacillus-based DFM containing Bacillus licheniformis 809 and B. subtilis 810 (BAC; n = 10; 2.2 × 10⁹ CFU of the mixture/g; Bovacillus, Novonesis, Lyngby, Denmark), and (ii) a TMR plus 165 g of protein-mineral supplement without DFM (CON; n = 10). Drylot pens were considered the experimental unit, with 4 to 5 calves per pen. Animals had free-choice access to the TMR offered daily at 0800 h. Feed samples were collected daily, and the refusals were removed weekly from the feed bunks. All samples were weighed, sampled, and dried to calculate dry matter intake (DMI). Calves shrunk BW was recorded on days 0 and 60 after 16 h fasting from water and feed. These values were used to calculate the average daily gain (ADG). Feed efficiency was calculated as the total experimental period BW gain divided by the total DMI for each pen. Blood samples were collected on days 0, 7, 14, 21, 28, 42, and 56 and analyzed for plasma concentrations of cortisol, nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), and glucose. Plasma samples from days 0, 7, 14, and 21 were also analyzed for haptoglobin concentrations. Hair samples were collected from the tail switch on days 0, 14, 28, and 42 and analyzed for cortisol concentrations. All data were analyzed using the MIXED procedure of SAS. Treatment was included as a fixed effect and pen(treatment) as a random effect; repeated-measures included time, treatment × time interaction, and calf(pen) as a random effect. There was a tendency for increased DMI in the BAC group compared to the CON group (P = 0.06), without any effect on the remaining performance parameters (P ≥ 0.50). A treatment × day interaction was observed for plasma cortisol concentration (P < 0.01), where animals from the CON group had increased cortisol levels on day 14. Mean plasma haptoglobin concentration was greater in CON compared to BAC cohorts (P = 0.03). Collectively, these findings suggest that Bacillus-based DFM enhanced feed intake and reduced plasma stress markers in feeder calves during a 60-day receiving program.