Effect of a direct-fed microbial (10-G Armor) on feedlot performance, carcass characteristics, and prevalence of in fed-beef heifers.

Crossbred beef heifers (= 1,394; initial shrunk body weight [BW] 291 ± 9.9 kg) were used to investigate the efficacy of 10-G Armor (Life Products, Inc., Norfolk, NE; 10-G) upon feedlot performance, carcass characteristics, and fecal and subiliac lymph nodes prevalence. Heifers were blocked by day of arrival and allocated to 1 of 20 pens ( = 70 heifers/pen) and assigned one of two treatments (10 pens/treatment): no direct-fed microbial (CON) or 2 g/heifer/d of and , respectively (Life Products, Inc., Norfolk, NE; 10-G). Twenty-four animals were randomly selected from each pen for sampling. Recto-anal mucosal swab samples (RAMS) were obtained at initial processing and harvest; subiliac lymph nodes were collected at harvest. In addition, pen surface fecal pats were collected and composited by pen (10 pats per composite, 5 composites per pen) on days 0, 52, 120, and 192. Data were analyzed as a generalized complete block design, and pen served as the experimental unit. No differences were observed in live growth performance metrics ( ≥ 0.55). Yield grade distributions did not differ between treatments ( ≥ 0.62); however, cattle fed 10-G tended ( = 0.06; 14.6% vs. 18.9%) to have fewer USDA Select carcasses and more ( = 0.09; 73.6% vs. 78.0%) USDA Choice carcasses. Cattle fed 10-G tended ( = 0.10; 9.2% vs. 12.3%) to have fewer liver abscesses and had fewer ( = 0.04; 5.3% vs. 8.5%) severe liver abscesses. prevalence of RAMS did not differ between treatments at initial processing ( = 0.97; CON = 11.6%, 10-G = 11.5%) or at harvest ( = 0.91; CON = 99.0%, 10-G = 98.6%); however, RAMS differed ( < 0.01) in prevalence between the two collection times. Cattle fed 10-G had a lower frequency of positive lymph nodes ( = 0.01; CON = 15.8%, 10-G = 7.4%) than CON. However, log (mpn/g) of lymph nodes did not differ between treatments at harvest ( = 0.34; CON = 0.73, 10-G = 0.34). These data indicate that cattle fed 10-G have decreased rates of severe liver abscesses without altering live animal performance or carcass characteristics. Supplementation of 10-G significantly reduced the prevalence rate of recovered from the subiliac lymph nodes. The factors responsible for the observed difference in the effects of 10-G on warrant further investigation.