The Effect of a Direct-Fed Microbial on Salmonella Prevalence and Concentration in Feedlot Steers and Assessing Differences in Salmonella Carriage Between Dairy-Beef and Native Cattle


August 2023

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Multiple studies were conducted to evaluate differences in Salmonella prevalence and concentration in feedlot cattle within the Texas Panhandle. The first study evaluated the efficacy of a direct-fed microbial upon feedlot performance, carcass characteristics, and Salmonella prevalence in subiliac lymph nodes (SLN). Yearling crossbred beef steers (n= 6400; initial body weight (BW) 358 kg) were used to investigate the efficacy of a direct-fed microbial upon animal growth performance, carcass characteristics, and prevalence of Salmonella in SLNs after a feeding duration of 182 days. Steers were allocated to 1 of 32 pens (n=200/pen) within 16 blocks, and assigned to 1 of 2 dietary treatments; no probiotic (CON) or 2 g/steer/d of Lactobacillus acidophilus, Enterococcus faecium, Pediococcus pentosaceus, Lactobacillus brevis and Lactobacillus plantarum providing a total of 1 billion CFU (Life Products, Inc., Norfolk, NE; 10-G). At harvest, SLNs were randomly obtained from 40 animals per pen for blocks 1 through 10. Data were analyzed as a randomized complete block design and pen served as the experimental unit. No differences (P ≥ 0.26) were observed between treatments for dry matter intake, final BW, average daily gain, or feed efficiency. When evaluating carcass characteristics, there were no differences (P ≥ 0.15) for hot carcass weight or liver abscess prevalence. However, dressed carcass yield tended to differ (P = 0.07) between treatments (CON - 64.51%, 10-G - 64.34%). No differences
(P ≥ 0.12) were observed for marbling score, ribeye area, backfat thickness, or USDA quality grade outcomes. Lower frequency (P = 0.03; CON - 37.95%, 10-G - 25.45%) of Salmonella positive subiliac lymph nodes was observed for cattle supplemented dietary 10-G, whereas log concentration of Salmonella did not differ (P = 0.31) between treatments (CON - 1.62 CFU/ln, 10-G - 1.32 CFU/ln). In conclusion, the supplementation of 10-G direct fed microbial did not influence live or carcass performance within this trial however prevalence of Salmonella positive subiliac lymph nodes was reduced. Fecal grabs and subiliac lymph nodes (SLN) were sampled from carcasses representing pens of beef (n = 25) and dairy-beef crossbred cattle (n = 25) within each of 10 different feedlots to investigate the prevalence and concentration of Salmonella at harvest, during the months of August, September, and October. Both beef and dairy-beef crosses were fed at the same feedlot within the Texas Panhandle, were harvested on the same day, and had longitudinal fecal and SLN samples collected. Immediately following exsanguination, via rectal palpation, fecal samples were collected, and immediately prior to chilling, SLN were obtained from 25 animals of each breed type, from each feedlot. Data were analyzed using a mixed model analysis, with breed type as a fixed effect and feedlot as a random variable. Differences (P < 0.01) were observed between cattle types for Salmonella prevalence within fecal samples at harvest. However, no differences (P ≥ 0.50) were observed for Salmonella prevalence within SLN or concentration within either fecal samples or SLN. When evaluating Salmonella outcomes by feedlot, differences (P ≤ 0.01) were observed for Salmonella prevalence and concentration within fecal samples, and Salmonella prevalence within SLNs. Salmonella prevalence within fecal samples ranged from 0 to 96% and concentration ranged from 0.00 to 6.28 CFU/g. Within subiliac lymph nodes, Salmonella prevalence ranged from 0.00 to 62.91% between feedlot locations. No differences (P = 0.47) were observed between feedlots for Salmonella concentration within SLN. In addition to the samples collected at harvest, fecal pat samples were collected from newly received cattle pens (n = 5 pens of beef; n = 5 pens of dairy-beef crosses) from 9 different feedlots in the Texas panhandle during a 5-week period between June and July 2023. No differences (P ≥ 0.22) in Salmonella prevalence or concentration were observed within fecal samples by breed type or by feedlot location. In conclusion, the only difference that appears to exist between native and dairy-beef cross animals is that of Salmonella prevalence, at harvest within fecal samples. In addition, stark differences exist for Salmonella prevalence and concentration across feedlots in samples collected at harvest. These outcomes suggest research should focus on reasons for variability in feedlot Salmonella rates in finishing cattle.



Agriculture, Animal Culture and Nutrition


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