Effects of Bacillus subtilis PB6 and/or chromium propionate supplementation on serum chemistry, complete blood count, and fecal Salmonella spp. count in high-risk cattle during the feedlot receiving and finishing periods

Authors: SMOCK, TAYLOR - Texas A&M University; SAMUELSON, KENDALL - Texas A&M University; Wells, James - Jim; Hales Paxton, Kristin; HERGENREDER, JERILYN - Kemin Industries, Inc; ROUNDS, PETER - Kemin Industries, Inc; RICHESON, JOHN - Texas A&M University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2020
Publication Date: 9/3/2020
Citation: Smock, T.M., Samuelson, K.L., Wells, J.E., Hales, K.E., Hergenreder, J.E., Rounds, P.W., Richeson, J.T. 2020. Effects of Bacillus subtilis PB6 and/or chromium propionate supplementation on serum chemistry, complete blood count, and fecal Salmonella spp. count in high-risk cattle during the feedlot receiving and finishing periods. Translational Animal Science. 4(3):1-11. https://doi.org/10.1093/tas/txaa164.
DOI: https://doi.org/10.1093/tas/txaa164

Interpretive Summary: Feedlot cattle that are sourced from auction barns are often high risk to disease and pathogens. This high risk is due to stresses from weaning, shipping, and handling that affect the immune function of the calf and these calves can be sources of Salmonella coming into the feedlot. After placement in the feedlot, these cattle are often very susceptible to develop bovine respiratory disease, or BRD, and often require multiple rounds of antibiotics to control the disease. As a preventative measure, antimicrobials have been used as mass treatments when high risk cattle arrive at the feedlot to reduce BRD. However, there is growing demand from consumers and producers to reduce antibiotic use in food animals, and as a consequence, a growing need for alternatives to antibiotics (ATA). In a study conducted in the Texas panhandle, high risk animals were either treated upon arrival with a placebo or with one of three ATA treatments. Chromium propionate treatments improved some white blood cell parameters and possible immune function, but this ATA had no effect on Salmonella levels in cattle. Cattle treated with a Bacillus probiotic did not exhibit improvements in white blood cell parameters, but these animals did exhibit reduced Salmonella shedding in Salmonella following treatment after arrival. This is the first report of an effective treatment to reduce Salmonella shedding in feedlot cattle.

Technical Abstract: The study objective was to determine the effects of Bacillus subtilis PB6 and/or chromium propionate supplementation on serum chemistry, complete blood count, and fecal Salmonella spp. count in high-risk beef cattle during a 56-d feedlot receiving period and the subsequent finishing period. Four truckload blocks of crossbred beef bulls (n=300) and steers [n=84; total n = 384; average initial body weight (BW) = 220 ± 16.2 kg] were sourced from regional auction markets and assigned randomly to treatments arranged in a 2 × 2 factorial. Blood samples were collected from two bulls nearest the median BW on arrival in each pen (n=96) and fecal samples were collected from cattle in block 3 (n=96). The generalized complete block design consisted of 12 pen replications per treatment with pen as the experimental unit. Treatments were: 1) negative control (CON); 2) 13 g per animal daily of prepared B. subtilis PB6 (CST); 3) 450 ppb dry matter (DM) chromium propionate (CHR); and 4) 13 g per animal daily of prepared B. subtilis PB6 and 450 ppb DM chromium propionate (CST+CHR). Treatments were top dressed in feed bunks daily using 0.45 kg per animal ground corn carrier immediately following feed delivery. Data were analyzed using mixed models with repeated measures. Day affected all serum chemistry variables (P <= 0.03) except total CO2 (P = 0.34) and all complete blood count variables during receiving (P >= 0.02) except percentage basophils (P >= 0.12). During the overall receiving period, serum calcium was decreased (P = 0.02) by CHR. Cattle fed CHR had greater total leukocyte count (P = 0.04) and neutrophil count (P = 0.02) during the overall receiving period. Fecal Salmonella spp. count was markedly reduced in cattle fed CST on day 28 (P = 0.01) and overall (P = 0.07). Overall, these data provide metabolic and hematologic insight into the unique challenges presented by lightweight, high-risk feeder cattle. Notably, CST was found to be effective in mitigating fecal enumeration and presumably replication of Salmonella spp. in the gastrointestinal tract.