Effect of a direct-fed microbial on animal performance, carcass characteristics and the shedding of Escherichia coli O157 by feedlot cattle

Feedlot steers (n = 288) were blocked by weight and fed a diet containing a direct-fed microbial (8 × 109 CFU Saccharomyces cerevisiae strain BP-31702; 5 × 108 CFU Lactobacillus acidophilus strain BT-1386/animal/day; DFM) or were not fed DFM (control). Steers in each treatment were housed in separate pens, with 12 animals per pen and 12 pens per cohort. Compared to controls, animals in the DFM cohort tended to have improved feed conversion (P=0.06) when expressed on a carcass weight basis although rate of gain, carcass yield and quality grades were similar. Fifteen freshly voided fecal pat (FP) samples per pen (10 g/pat; 150 g/pen) were subsampled prior to administration of the DFM (background; d-2) and on 3 different occasions after DFM administration (d 30, 57, and 85). Fecal grab (FG), hock swab (HS; 100 cm2-area), and perineum swabs (PS; 100 cm2-area) were taken from each animal prior to shipment for slaughter (d 119 and 140). Perineum swabs were 4.76 and 2.04 times more likely (P=0.01) to have Escherichia coli O157 present when compared to HS and FG, respectively. In the present study, PS was more sensitive than FG or HS at detecting E. coli O157 in feedlot cattle, but no differences between DFM and control cohorts were observed in E. coli O157 in post-treatment samples. Although feed conversion on a carcass weight basis tended to be improved by feeding the DFM, additional large-scale commercial feedlot studies will be necessary to determine cost-effectiveness, dose-dependency, and efficacy of this DFM product for enhancing growth and possibly mitigating E. coli O157 in feedlot cattle.