2024-01-042024-01-042023-12https://hdl.handle.net/2346/97357The inestimable economic loss in carcass value and feedlot performance associated with liver abscess in feedlot cattle has become a prominent and troublesome issue due to the multifactorial, sub-clinical nature of this disease. The first objective of this study was to determine the effects of liver abscess presence and severity on beef × dairy crossbred heifers on growth performance and carcass characteristics, while the second objective of this study was to investigation potential blood-based biomarkers for live-animal detection of liver abscess. A total of 1,984 beef × dairy heifers (initial body weight [BW] = 334.8 ± 4.6 kg) were assessed in a prospective cohort study. Treatment comparisons were assorted based on liver scores at time of harvest as follows: 1) non-abscessed (0); 2) 1 to 2 small abscesses (A-); 3) multiple small abscesses or 1 to 2 large abscesses (A); 4) and multiple large abscesses, open abscess, or signs of gut pile and/or diaphragm adherence (A+). Heifers (N = 200) which fit the treatment description (0 = 110; Abscessed [A-, A, or A+] = 97) had liver weights recorded and blood samples collected at harvest for modeling of potential predictors of the liver abscess condition. The experimental design, a prospective cohort study, used animal as experimental unit and included fixed effects of liver score and random effects of sorted pen (n = 30) nested within harvest dates (n = 9). For carcass outcomes by liver score and abscess size, results indicated hindered carcass performance in heifers with severe abscess (A+ or large abscess). Heifers scored as A+ yielded an economic loss of $70.51/hd in overall carcass value (sum of by-product and carcass pricing). While the live-animal performance of these same heifers also indicated the greatest hinderance in performance was associated most with heifers with sever abscess (A+ or large abscess), where the largest majority of cattle with severe abscess gained less than 0.45 kg per day (P = 0.02). Furthermore, liver weight was affected by liver abscess, with A+ scores weighing as much as 1kg or more than healthy livers (0; P < 0.01). In a binary system (abscessed or not), heifers with liver abscess had lesser values of LYM and WBC concentration (P < 0.01) but elevated PLR (P < 0.01). Serum chemistry measures were not affected by abscess presence or liver score (severity; P ≥ 0.06). In univariate modeling of CBC measures, only WBC concentration was accurate (65.85%; P < 0.01); however, not deemed an acceptable biomarker due to its’ poor specificity (54.79%). Using machine learning algorithms for modeling abscess condition, the LogitBoost model produced the greatest accuracy (80.65%; P < 0.01) and specificity (85.71%). An accurate blood test that allows for the detection of liver abscess during the finishing phase may allow for therapeutic management or alternative marketing of cattle; however, the marginal accuracy demonstrated in this study combined with the impracticality and cost of analyzing a blood sample may not be feasible. Regardless, the most explanatory CBC variables in cattle with abscessed livers were suggestive of an immune response. Overall, both late live-animal performance and carcass outcomes were negatively impacted by liver abscess in beef × dairy heifers and induced economic losses as much as $70.51/hd. Minor response in serum chemistry occurs as a result of liver abscess, while immune response measures including LYM and WBC should be further explored.Application/pdfenliver abscessbiomarkersbeef-dairyThesisAccess is not restricted.