Lameness in feedlot cattle.

This article examines the various causes of lameness in feedlot cattle, with an emphasis on clinical signs, treatment, and prevention. Specific conditions are discussed, including interdigital necrobacillosis, laminitis, feedlot injuries, and feedlot lameness associated with Mycoplasma bovis. Immune management of the foot is also reviewed.     

Acidosis in feedlot cattle.

Mortality from digestive diseases in feedlot cattle is second only to that from respiratory diseases. Acidosis is a major digestive disorder and is likely to continue because of ongoing attempts to improve the efficiency of beef production by feeding more grain and less roughage. Subacute acidosis is the most prevalent form of acidosis in feedlots but is difficult to diagnose because of the absence of overt clinical signs. Control of acidosis is achieved largely by sound nutritional management. No single strategy or solution exists; however, an effective management strategy should factor in dietary formulation, a consistent feeding program, prudent bunk management, use of nonstarch by-products, and feed additives to minimize pen-to-pen and animal-to-animal variations in feed intake.     

Abomasal erosions in feedlot cattle.

The abomasa of 1,949 slaughtered feedlot cattle, 45 necropsied feedlot cattle that died 2 to 45 days after arrival, and 45 necropsied pastured cattle were opened and examined. Of these organs, 484, 1, and none, respectively, contained erosions. The slaughtered cattle were fattened at 3 locations: 1,305 with 430 eroded abomasa were fed a ration of corn in northeastern Colorado; 144 cattle with 4 affected abomasa fed a ration of milo in south-central Arizona; and 500 cattle with 50 affected abomasa fed a ration of milo and corn in northwestern Texas. The red-brown lesions developed late during the second semester of fattening and were located mostly on fundic folds. Those on fold edges were linear and were 2 to 15 cm long, whereas those on fold sides were punctate and were 2 to 15 mm in diameter. Normal fold edges contained fewer goblet cells and less surface mucus than did fold sides. Eroded folds had disruption of surface epithelium, damage to endothelial cells, and dilated, thrombosed, congested, and ruptured capillaries. Mean pH values of 16 normal and 17 eroded abomasa were 4.7 and 3.9, respectively. Necrosis of all tissue toward the mucosal surface of erosions was extensive. The cause of gastric erosion in cattle is not known.     

Liver abscesses in feedlot cattle.

Liver abscesses in feedlot cattle result from aggressive grain-feeding programs and are influenced by a number of dietary and management factors. They have a major economic impact on the feedlot industry because of liver condemnation and reduced animal performance and carcass yield. Ruminal lesions resulting from acidosis usually are accepted as the predisposing factors. Generally, control of liver abscesses in feedlot cattle has depended on the use of tylosin, which reduces abscess incidence by 40% to 70%. However, new methods and products for liver abscess control are needed. Corn milling by-products that are less fermentable may aide in the quest for cattle production techniques that lead to lower usage of antimicrobials. A vaccine is also commercially available.     

Aflatoxicosis in feedlot cattle

Aflatoxicosis was diagnosed in lightweight feedlot cattle fed aflatoxin-contaminated cottonseed or gin trash. Clinical signs of hepatic damage and death were recorded for more than 200 of the 14,000 animals in a feedlot. Aflatoxin concentration in feedlot products fed to these cattle ranged from 96 to 1,700 ng/g. Diagnosis was based on the correlation of characteristic microscopic liver lesions, high concentration of aflatoxin in cottonseed feed products, and isolation and detection of aflatoxin B1 and aflatoxin M1 in urine and liver from affected calves. This report describes a large-scale outbreak of aflatoxicosis and demonstrates the need for careful quality control of feed products susceptible to aflatoxin contamination.     

Predicting bovine respiratory disease outcome in feedlot cattle using latent class analysis

Bovine respiratory disease (BRD) is the most significant disease affecting feedlot cattle. Indicators of BRD often used in feedlots such as visual signs, rectal temperature, computer-assisted lung auscultation (CALA) score, the number of BRD treatments, presence of viral pathogens, viral seroconversion, and lung damage at slaughter vary in their ability to predict an animal’s BRD outcome, and no studies have been published determining how a combination of these BRD indicators may define the number of BRD disease outcome groups. The objectives of the current study were (1) to identify BRD outcome groups using BRD indicators collected during the feeding phase and at slaughter through latent class analysis (LCA) and (2) to determine the importance of these BRD indicators to predict disease outcome. Animals with BRD (n = 127) were identified by visual signs and removed from production pens for further examination. Control animals displaying no visual signs of BRD (n = 143) were also removed and examined. Blood, nasal swab samples, and clinical measurements were collected. Lung and pleural lesions indicative of BRD were scored at slaughter. LCA was applied to identify possible outcome groups. Three latent classes were identified in the best model fit, categorized as non-BRD, mild BRD, and severe BRD. Animals in the mild BRD group had a higher probability of having visual signs of BRD compared with non-BRD and severe BRD animals. Animals in the severe BRD group were more likely to require more than 1 treatment for BRD and have ≥40 °C rectal temperature, ≥10% total lung consolidation, and severe pleural lesions at slaughter. Animals in the severe BRD group were also more likely to be naïve at feedlot entry and the first BRD pull for Bovine Viral Diarrhoea Virus, Bovine Parainfluenza 3 Virus, and Bovine Adenovirus and have a positive nasal swab result for Bovine Herpesvirus Type 1 and Bovine Coronavirus. Animals with severe BRD had 0.9 and 0.6 kg/d lower overall ADG (average daily gain) compared with non-BRD animals and mild BRD animals (P < 0.001). These results demonstrate that there are important indicators of BRD severity. Using this information to predict an animal’s BRD outcome would greatly enhance treatment efficacy and aid in better management of animals at risk of suffering from severe BRD.     

Association of bovine respiratory syncytial virus with atypical interstitial pneumonia in feedlot cattle

Thirty-three cattle with fatal respiratory tract disease were examined for gross and histologic lesions and for the presence of viral and bacterial agents in the lungs. Fifteen cattle had lesions characteristic of atypical interstitial pneumonia (AIP), and 18 had other respiratory tract diseases, including infectious bovine rhinotracheitis, shipping fever pneumonia, bronchopneumonia, pulmonary abscess, and edema of the trachea. Gross necropsy findings in the cattle with AIP were uncollapsed and emphysematous lungs; histopathologic findings included interstitial edema, thickening of alveolar walls, hyaline membrane formation, and hyperplasia of type-II pneumonocytes. The infective agents found in the lungs of the 33 cattle included bovine respiratory syncytial virus, bovine herpesvirus type 1, Pasteurella sp, mycoplasmas, and Corynebacterium pyogenes. Bovine respiratory syncytial virus was detected by use of immunofluorescence and immunoperoxidase on lung tissue sections; bovine herpesvirus type 1 was detected by these techniques and by isolation of the virus. Bovine respiratory syncytial virus was significantly (P = 0.01) associated with lesions of AIP (11 of 15), compared with those of other respiratory tract diseases (5 of 18).     

Hypovitaminosis A in feedlot cattle

Hypovitaminosis A was diagnosed in a group of feedlot cattle that had been fed a diet low in carotene for 18 months. The primary signs of disease in the cattle were poor weight gain, ataxia, convulsions, night blindness, and total blindness. Serum vitamin A concentrations were used to confirm the diagnosis. The cattle were treated orally and intramuscularly with vitamin A, and the less severely affected herd members recovered rapidly.