EFFECT OF A DIRECT-FED MICROBIAL ON FEEDLOT PERFMORMANCE, CARCASS CHARACTERISTICS AND PREVALENCE OF SALMONELLA IN FED-BEEF HEIFERS

Salmonella is a naturally occurring bacteria that is known to cause upwards of 1.35 million cases of foodborne illnesses annually. Ground beef products may be manufactured from trimmings containing Salmonella infected lymph nodes, which has led to pending rulemaking by USDA-Food Safety and Inspection Service to declare Salmonella as an adulterant. Direct-fed microbials are a pre-harvest intervention for reduction of Salmonella. The objective of this study was to determine the efficacy of a direct-fed microbial upon the prevalence and enumeration of Salmonella in feces and lymph nodes. Heifers (n=1,394; 291 ± 9.9 kg) were blocked by day of arrival and randomly allocated to one of two treatments (0 or 2g/animal/d; CON and 10-G, respectively) with ten pens per treatment. Heifers fed 10-G were provided 1 billion CFUs per animal per day of Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum. Twenty-four animals were randomly selected from each pen for Salmonella sampling. Rectoanal 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 170. Mixed models were used to analyze live performance, carcass characteristics and Salmonella prevalence and concentration with treatment used as fixed effect, block
used as random effect and pen as experimental unit. Repeated measures was used to analyze Salmonella prevalence and concentration across time using the unstructured covariance structure. Dry matter intake (P = 0.63), average daily gain (P = 0.69), gain:feed (P = 0.81) and final body weight (P = 0.79) did not differ between treatments. Neither morbidity (P = 0.90) nor mortality and railer rates (P = 0.55) were different between treatments. Hot carcass weight (P = 0.14), dressed carcass yield (P = 0.53), 12th rib fat depth (P = 0.73), ribeye area (P = 0.13), calculated empty body fat (P = 0.71) or marbling score (P = 0.20) were not different between treatments. Yield grade distributions did not differ between treatments (P ≥ 0.44), however cattle fed 10-G tended (P = 0.06; 15.78 vs 20.34%) to be represented by fewer USDA Select carcasses and more (P = 0.09; 73.62 vs 77.97%) USDA Choice carcasses. Livers from cattle fed 10-G tended (P = 0.10; 12.26 vs 9.23%) to have a lower frequency of abscesses when compared to CON. Heifers fed 10-G also had fewer (P = 0.04; 5.27 vs 8.51%) severe liver abscesses. Salmonella prevalence of RAMs did not differ between treatments at initial processing (P = 0.92; CON = 11.6%, 10-G = 11.5%) or at harvest (P = 0.92; CON = 99.0%, 10-G = 98.6%), however RAMs differed (P < 0.01) in Salmonella prevalence between the two collection times. Likewise, Salmonella log (mpn/g) of RAMs did not differ between treatments at initial processing (P = 0.63; CON = 0.28, 10-G = 0.30) or at harvest (P = 0.63; CON = 4.40, 10-G = 4.05), while log (mpn/g) of Salmonella increased (P < 0.01) over the feeding period. Moreover, composited pen level fecal pats were similar for Salmonella prevalence (P = 0.73; CON = 69.0%, 10-G = 67.0%) between treatments, but prevalence increased (P < 0.01) sharply during the initial 52 d then plateaued during the remainder of the finishing period. However, Salmonella prevalence differed (P < 0.01) among sampling days. Cattle fed 10-G had a lower frequency of Salmonella positive lymph nodes (P = 0.01; CON = 15.80%, 10-G = 7.41%) than CON. However, Salmonella log (mpn/g) of lymph nodes did not differ between treatments at harvest (P = 0.34; CON = 0.73, 10-G = 0.34). This data indicates that cattle fed 10-G decreased rates of severe liver abscesses without altering live animal performance or carcass characteristics as well as fewer Salmonella positive lymph nodes, which in turn can likely improve public health by reducing the number of foodborne illnesses caused by Salmonella.