Association of liver abscess with demographic factors, gross pathology, and gastrointestinal histologic morphology in feedyard mortalities.

Liver abscesses (LA) are a major cause of hepatic condemnation in feedlot cattle (~ 20% beef carcasses) creating concerns surrounding carcass contamination, impaired performance, and antimicrobial stewardship. Due to antemortem limitations in determining LA status, risk factors for LA during the feeding phase are poorly characterized. The objective was to identify factors associated with the presence of LA in feedlot mortalities at necropsy, including demographic factors, and gross and histologic gastrointestinal (GI) morphologic lesions. Systematic necropsies (n = 900) were performed in 6 central U.S. commercial feedyards (June/July 2022 and 2023). Gross morphologic diagnoses were determined by technicians and confirmed by a veterinarian. Formalin-fixed sections of rumen, small intestine (SI), and spiral colon (SC) were collected from LA cases (n = 40) and time-, feedlot-matched controls (CON; no LA; n = 40). Demographic data collected included sex, days on feed at death (DOF), arrival weight, number of disease treatments, and estimated weight at death. Morphologic features were measured in GI tissues using hematoxylin and eosin stain and alcian blue stain was used to evaluate goblet cell area in SI and SC. General and linear mixed-effects models were used to evaluate LA association with demographic, gross lesions, and histomorphologic changes identified in LA and CON cases. Steers had greater (P < 0.01) probability of LA than heifers (0.16 vs. 0.06, respectively). Dairy-influenced cases had a greater (P = 0.04) probability of LA than traditional beef breeds (0.30 vs. 0.03, respectively). Cases that were 101 + DOF had a greater (P < 0.01) probability of LA than those <50 DOF (0.20 vs. 0.06, respectively). Cases with peritoneal adhesions had a greater (P < 0.01) probability of having LA than cases without peritoneal adhesions. Liver abscess cases had wider (P = 0.03) rumen papillae and thinner (P = 0.05) keratin layer lining papillae in the rumen, and shallower (P = 0.02) crypts and thinner (P = 0.02) propria in the SI than CON cases. A tendency (P = 0.08) for LA cases to have a lower percent area of goblet cells in the SI than CON cases was observed. No differences in SC morphology were observed. Although results are biased to only feedlot mortalities, these findings indicate an association of LA with histomorphologic measures, gross pathology, and demographic factors. Further investigation is required to better understand factors influencing LA formation in feedlot cattle.