EXPERIMENTS TOWARDS A GREATER UNDERSTANDING OF THE LIVER ABSCESS COMPLEX IN FED BEEF
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Four trials (national liver audit, a multiple response feedlot questionnaire, association of liver abscesses to carcass trim and quality, and association of blood chemistry variables and liver abscess outcome) were conducted to examine national liver abscess incidence, determine conditions at the feedyard that may affect these outcomes, quantify trim losses and carcass characteristics associated with liver abscesses, and identify blood chemistry variables that may be associated with liver abscess incidence in fed Holstein steers. The first trial involved observational liver audits that occurred at 7 fed beef (n = 130,845 livers evaluated) and 4 cull cow (n = 30,646 livers evaluated) processing facilities. Processing facilities were selected to target the greatest frequency of Holsteins harvested per region and were audited for one week. At each processing facility, 30 (10 A-, 10 A, 10 A+) intact liver abscess samples were collected and cultured for Fusobacterium necrophorum, Trueperella pyogenes, and Salmonella enterica. Average liver abscess incidence was 20.3% for cattle harvested at fed beef processing facilities; processors in the Pacific Northwest had the greatest (P < 0.01) abscess incidence rate (33.8%) whereas those in the Northeast had the fewest liver abscesses (10.0%). Average liver abscess incidence was 17.6% for cull beef processing facilities. Within cattle type, fed Holsteins had greater (P < 0.01) abscess incidence rates (25.0%) than fed beef steers (18.2%) or heifers (19.1%). Cull dairy cows, cull bulls, and cull range cows had total abscess incidence rates (19.3%, 19.8%, and 16.7%, respectively) similar to fed steers and fed heifers. Fusobacterium necrophorum subsp. necrophorum was present in 79.9% of samples collected from fed beef processors and 76.9% of samples from cull beef processors, whereas Trueperella pyogenes was present in 14.8 of samples from fed beef processors and 8.8% of samples from cull beef processors. Salmonella enterica was present in 27.5% of abscess samples collected from fed beef processors and 16.5% of samples from cull cow processors. Fusobacterium necrophorum, regardless of subspecies, was present at every processing facility; whereas S. enterica tended to occur in processing facilities in warm and dry climates and T. pyogenes tended to occur in processing facilities in colder and wetter climates. In order to associate conditions at the feedyard with abscess outcomes observed at the processing facility, the second trial utilized survey data that were assimilated to corresponding individual lots of fed cattle. Thirteen nutritionists participated in the survey representing 43,255 animals, in 321 lots, from 32 individual feedlots throughout the major cattle feeding areas of the U.S. The survey contained 57 questions divided into information categories that included: general (n = 13); health (n = 6); source and background (n = 7); growth promoting technologies (n = 3); diet (n = 10); feeding management (n = 6); cattle management (n = 8); and liver abscess control technologies (n = 4). Cattle type (beef or dairy; Adj. R2 = 0.13), diet dry matter percentage (Adj. R2 = 0.11), G:F (Adj. R2 = 0.11), mortality (Adj. R2 = 0.07), and tylosin supplementation (yes or no; Adj. R2 = 0.06) all yielded univariate equations capable of predicting total abscess percentage. Using the maximum likelihood method in the CALIS Procedure of SAS, the full model to predict total liver abscess incidence was: total liver abscess percentage = 113.5 – (217.39 × G:F) – (18.48 × cattle type [1 = native beef; 0 = Holstein]) – (46.35 × Diet DM, %) – (14.39 × tylosin supplementation [1 = yes; 0 = no]), and accounted for 34% of the variation to predict total liver abscess incidence. In the third trial, fed Holsteins were tracked through two commercial processing facilities, one in the High Plains region (n = 1,073) and one in the Central Plains region (n = 1,070). Liver abscesses were visually assessed and scored according to a modified scoring system based on the Elanco Liver Check Service; simultaneously, lungs were manually palpated to assess degree of consolidation and fibrin tag formation and its association to liver abnormality. Finally, carcass trim was weighed from carcasses moved off-line for zero tolerance trimming. Carcass and viscera values were assigned using USDA market reports and adjusted based on viscera condemnations along with premiums and discounts for quality and yield outcomes. Cattle exhibited liver abnormality rates of A- = 3.73%, A = 7.28%, A+ = 7.56%, A+Adhesion (A+AD) = 17.50%, A+Open (A+OP) = 4.39%, A+Adhesion/Open (A+AD/OP) = 3.92%, and Contamination = 6.16%, with 49.46% of all livers being edible. Hot carcass weight was reduced (P < 0.01; -25.1 kg, -6.6%) in carcasses that had an A+AD/OP liver abscess as compared to carcasses with edible livers. Carcasses with A+AD or A+OP liver scores had increased (P < 0.01) carcass trim (3.92 and 3.39 kg, respectively), when compared to carcasses with edible livers (0.38 kg). A greater degree (P < 0.001) of lung consolidation was observed in carcasses with A+AD and A+AD/OP liver scores than carcasses with edible livers. Livers with abscesses yielded an average loss to the beef processor of $3.25 per condemned liver ($3.89/edible liver vs $0.64/condemned liver). Given the 44.38% incidence of liver abnormalities, and the 25.81% incidence of open and adhered abscesses observed, fed beef processors lose an estimated $21.8 million annually in condemned viscera due to liver abnormalities in fed Holsteins. Although not different (P = 0.27), carcasses with A+AD liver outcomes were worth 4.9% less (-$73.93/carcass) than their edible counterparts, and carcasses with A+OP livers were worth 4.6% less (-$69.65/carcass) than carcasses with edible livers. For the final trial, blood samples for complete blood count (CBC) and sera were collected from fed Holsteins (n = 153) approximately 30 s after exsanguination; liver abscesses were visually assessed after evisceration. Greater (P = 0.03) hot carcass weights were observed from carcasses with minor (387.1 kg) abscesses, which were 5.41% heavier than carcasses with major abscesses (366.2 kg) but not different (P > 0.10) from carcasses with no liver abnormality (381.8 kg). Of the CBC variables analyzed, platelet counts were increased (P = 0.02) whereas hemoglobin and hematocrit values (P < 0.01) were decreased in carcasses with major abscesses (214 K/uL, 12.9 g/dL, 41.0%) when compared to carcasses without abscesses (137 K/uL, 13.8 g/dL, 43.4%). Serum analysis indicated that carcasses with major abscesses had increased (P < 0.01) globulin (5.8 g/dL) concomitant with decreased (P ≤ 0.03) sodium (141 mmol/L), albumin (2.8 g/dL), alanine aminotransferase (19 u/L) and aspartate aminotransferase (89 u/L) when compared to carcasses with no liver abscess (5.2 g/dL; 142 mmol/L; 3.0 g/dL; 21 u/L; 97 u/L, respectively). Logistic regressions equations using CBC variables (platelets and hemoglobin) or serum variables (aspartate aminotransferase and total protein), yielded equations that were able to explain 72% (c-statistic = 0.72) and 69% (c-statistic = 0.69) of the area under the curve, respectively, for predicting major liver abscesses. In conclusion, total visceral losses ($/animal) did not differ by region (P = 0.40) or cattle type (P = 0.85), conservative estimates indicate that liver abscesses and other liver abnormalities cost the beef industry approximately $60 million annually in viscera losses. While predictive equations revealed that dietary factors can contribute to, and likely exacerbated liver abscess incidence, additional factors, beyond dietary measures, contributed to the multifactorial disease. Models generated were unable to explain more than 40% of the variation involved in predicting either total or major abscess incidence, indicating that liver abscesses are likely a multifactorial disease influenced beyond dietary factors alone. Holsteins are an important segment of the beef industry and are disproportionally affected by liver abscesses, when compared to traditional (non-Holstein) beef. Unless the liver abscess issue is addressed by the fed beef industry, Holsteins will continue to incur greater financial risk to both cattle feeders and processors. Finally, cattle with major liver abscesses undergo metabolic differentiation which can be detected in whole blood and serum at slaughter and identifying blood parameters that could be used to diagnose liver abscesses, during the live phase, may have useful implications for cattle welfare and feedlot management.