Undifferentiated fever in a Southern Alberta feedlot calf

On the morning of November 3, 2010, a mixed breed stocker calf at 57 days on feed, housed in a pen of 300, at a 30,000 head Southern Alberta feedlot, was observed to be depressed, gaunt, and reluctant to move. The heifer calf was segregated from pen mates and brought to an onsite hospital facility for further evaluation. Examination of treatment history revealed a previous episode of undifferentiated fever at 35 days on feed. Physical examination resulted in a problem list consisting of dehydration, depression, dyspnea, fever, inappetance, and nasal discharge. Subjective evaluation resulted in classification of the calf as being "sick." However, no clinical signs could be attributed to any organ system other than the respiratory tract, resulting in a presumptive diagnosis of undifferentiated fever (UF). Upon arrival at the feedlot, the heifer had been assessed to be at high risk of developing undifferentiated fever, due to exposure to risk factors including: purchase at an auction market, comingling with animals from multiple sources, and being of a young age. Metaphylactic treatment with tilmicosin (Micotil) was performed. In keeping with the feedlot's health management protocols, initial treatment for undifferentiated fever, at 35 days on feed, consisted of subcutaneous injection with tulathromycin (Draxxin). The undifferentiated fever relapse was treated with enrofloxacin (Baytril). Undifferentiated fever, also commonly referred to as bovine respiratory disease or shipping fever, is the most economically important disease affecting feedlot animals in North America (Booker et al, 1998). Bovine respiratory disease accounts for 70-80% of morbidity and 40-50% of mortality in feedlot animals. Major costs associated with the disease are attributed to preventative measures, treatment, and death loss (Jim et al, 1993). UF is a multifactorial disease, caused by a combination of viral and bacterial infectious agents in conjunction with a suppressed immune system, due to environmental and physiologic factors (Snowder et al, 2006). The major viral pathogens include bovine herpesvirus-1, bovine respiratory syncytial virus, bovine parainfluenza type 3, and bovine viral diarrhea virus. Bacterial pathogen implicated in bovine respiratory disease are Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis (Griffin et al, 2010). Control efforts have focused on reducing stress to the animals as they transition to the feedlot, as well as medical intervention, including vaccination and antibiotic usage (Booker et al, 1998).

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