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Abstract
Growing pressure from consumers and legislation to reduce antibiotic usage in cattle production has left producers needing natural alternatives like microbial supplements that are capable of maintaining animal health and performance during times of stress such as the weaning and receiving periods. Therefore, the objective of this research was to investigate the impacts of pre- and post-weaning dietary supplementation of grain, with or without the addition of a Lactobacillus acidophilus fermentation product (LAFP) microbial supplement, on beef steer performance, gastrointestinal fermentation, and immune response. Sixty suckling steers (211.4 ± 21.2 kg; 173 ± 17 d) were selected and assigned to 1 of 3 dietary treatments: (1) CONTROL – calves were on pasture with dam (2) CREEP – same as CONTROL plus given access to ad libitum creep feed (3) LAFP – same diet as CREEP but with LAFP added. Dietary treatments were administered for 70-d prior to weaning. During this period, the first study was designed to evaluate the impacts of dietary treatment on growth performance and composition, feed intake, daily activity, and gastrointestinal volatile fatty acid (VFA) profiles of the steers. Results from this study indicated that creep feed supplementation tended to improve steer growth performance over CONTROL. Moreover, the addition of LAFP to the creep feed tended to improve feed efficiency, which could be due in part to the numerically lower feed intake and greater VFA concentrations, especially propionate, reported in the gastrointestinal tracts of LAFP steers compared to CREEP. For the second study, the same steers were weaned and transported to a new facility where they were subjected to a lipopolysaccharide immune challenge on day 4. Overall, results from the second study suggested that while the challenge model employed was successful, as indicated by changes in immune markers over time, there were no significant differences in the responses across the different dietary treatments, indicating that all steers responded similarly to the immune challenge regardless of pre-weaning dietary treatment. In conclusion, this research provides the cattle industry with valuable information regarding the impacts of dietary management and microbial supplementation on steer performance and immune function in response to an immune challenge.