The effect of respiratory disease on the performance of cattle in two South African feedlots

Abstract

Bovine Respiratory disease (BRD) accounts for the highest proportion of morbidities and mortalities in feedlot cattle. Since both clinical and subclinical disease is known to affect growth performance, it is clear that both should be accounted for in estimating the overall effect of BRD on performance in feedlot cattle. To our knowledge there have been no studies estimating the true impact of BRD on the economy of the South African feedlot industry, including both the direct costs of treatment, labour and mortalities and the hidden costs of lower gains due to BRD. This was an observational study, utilising predominantly routinely collected data from two commercial cattle feedlots. Assessment of the effect of treatment for BRD on outcome variables (performance parameters and prevalence of lesions) took the form of a prospective cohort study. Assessment of the effect of lung lesions at slaughter on performance took the form of a cross-sectional study, in which the presence of lung lesions and performance parameters were recorded at slaughter. Assessment of the overall effect of BRD on performance was then done using a combined case definition (treatment for BRD and/or lung lesions present at slaughter). Slaughter data for 2036 animals were available for the final analysis. Mean average daily gain (ADG) for all animals was 1.504 kg for the period from processing to slaughter. Average days on feed (DOF) was 136 days. Peak incidence of respiratory disease in the feedlots occurred on Day 18 after arrival. A total of 22.7% of animals were treated for clinical respiratory disease. No mortalities occurred due to BRD during this period. A total of 42.8% of animals had lung lesions present at slaughter. Of animals never treated for respiratory disease, 38.5% had lung lesions at slaughter. Of animals that had lung lesions at slaughter, 69.5% had never been treated for respiratory disease. Using the combined case definition, the estimated incidence of BRD during this study was 52%. It was found that pulling for BRD was associated with an overall decrease in ADG of 19 g for the whole period in the feedlot. The presence of lung lesions (bronchopneumonia and/or adhesions/pleuritis) at slaughter was associated with a decrease in ADG of 27 g for the whole feeding period. The occurrence of BRD (using the combined case definition) was associated with a decrease in ADG of 28 g for the period from processing to slaughter. This translated into a hidden cost of R14.93 per animal in the feedlot. This was nearly equal to the direct variable cost/animal entering the feedlot of R15.40. The total loss due to BRD was estimated to be R30.30 per animal entering the feedlot with an estimated cost of about R40m per year to the South African feedlot industry.