PS13-8. Impact of Natural Antibody-Based Direct-Fed Microbial on Feedlot Performance and Carcass Characteristics in Finishing Beef Cattle.

Abstract Direct-fed microbial products containing naturally derived immunoglobulin Y (IgY) have been proposed as a nutritional strategy to support gastrointestinal function and improve growth performance in beef cattle through modulation of the rumen and intestinal environments. The objective of this study was to evaluate the effects of an IgY-containing direct-fed microbial on feedlot performance, carcass characteristics, and liver abscess incidence and severity in finishing cattle. One-hundred and sixty Angus-cross steers (initial body weight [BW] = 471 ± 30.8 kg) were stratified by BW and randomly assigned to 1 of 2 treatments across 8 pens: control or direct-fed microbial supplement (n = 4 pens per treatment). Cattle were fed a total mixed finishing ration ad libitum. Refusals were collected weekly by pen to determine dry matter intake (DMI), and BW was recorded on d 0, 26, 57, 84, 112, 140, and 161. At the conclusion of the feeding period, cattle were harvested at a commercial abattoir, and carcass data were collected. Pen served as the experimental unit for all performance and carcass analyses. Dry matter intake, BW, average daily gain (ADG), gain-to-feed ratio (G:F), hot carcass weight (HCW), ribeye area (REA), fat thickness (FT), yield grade (YG), and marbling score (MARB) were analyzed using the MIXED procedure of SAS 9.4 (SAS Inst., Cary, NC) with the fixed effect of treatment. For BW, day and the treatment × day interaction were included as fixed effects. Pen was included as a random effect. Liver abscess presence and severity were analyzed using the GLIMMIX procedure, with binomial and multinomial distributions, respectively. Significance was declared at P ≤ 0.05. No differences were observed for DMI, ADG, or G:F (P ≥ 0.86). Body weight increased over time for both treatments (day; P < 0.01), with no treatment effect or treatment × day interaction (P = 0.96). No differences were detected for HCW, REA, FT, YG, or MARB (P ≥ 0.22). Additionally, no treatment effects were observed for liver abscess presence or severity (P ≥ 0.68). Overall, supplementation with an IgY-containing direct-fed microbial did not improve feedlot performance, carcass characteristics, or liver abscess outcomes under the conditions of this study. However, no negative effects on performance or carcass traits were observed. Further research may be warranted to evaluate potential impacts on pathogen shedding and food safety-related outcomes, including Escherichia coli prevalence on hide and carcass surfaces.