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Practical use of thoracic ultrasonography at feedlot arrival to identify high-risk BRD batches in suckler calves
Tejero, C., Elvira, L., Lillo, J...
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Objectives
Bovine Respiratory Disease (BRD) is the most important disease in veal industry. The assessment of lung health of suckler calves’ batches at their arrival to the rearing facilities is key for decision making and implementation of prevention and metaphylactic protocols for BRD control. However, classification and identification of high-risk BRD batches (30% prevalence) continues to be a major challenge. BRD diagnosis based on clinical signs is inaccurate (61.8% sensitivity and 62.8% specificity; White, 2009).
The use of thoracic ultrasound (US) scanning to evaluate lung health has demonstrated to be a high sensitivity and specificity tool (79,4% and 93,9%, respectively; Buczinski, 2015). A previous study in 811 veal calves using this technique at arrival (Tejero et al., 2019) showed an average of 21% moderate and 10% severe lung lesions. However, large variability was found among batches (P <0.05).
In high-risk BRD batches, metaphylactic treatment has the potential to reduce the number of animals infected with a susceptible bacterial pathogen, clinical or subclinical, reducing the disease challenge in the environment for non-infected animals and limiting disease spread (Nickel, 2010). Thoracic US scanning has the potential to identify high-risk BRD batches where metaphylactic treatment is justified. However, under field conditions, thoracic US scanning is time consuming. The main objective of this study was to evaluate if the selection of a representative sample of animals for thoracic US scanning provides a reasonable accuracy to identify high-risk BRD batches.
Materials and methods
The number of calves to be sampled per batch was calculated using free epidemiological software (https://epitools.ausvet.com.au). An estimated prevalence of 30% (high-risk BRD) using a confidence level of 95% and an accepted error of 10% for calves with lung lesions equal or higher than 3, using Adams and Buzsinski (2015) scoring system, was used.
To check the practical use of the sampling table created, a simulation of this sampling procedure was done in 12 batches where thoracic US was assessed in 100% of the animals. A randomization procedure (Excel, Microsoft Office) was used to select the different sampling groups, performing 10 random samples of each batch in order to measure the degree of success to predict whether the batch was a high-BRD risk one.
Results
The percentage of calves sampled ranged from 21% to 62% for a 300 or 50 suckler calves’ batch respectively.
Our Database of 12 batches, where thoracic US was performed in a 100% of calves at arrival, was used for random selection of calves. Real batches included 12 to 51% of calves affected with score higher than 3 (moderate and severe cases). Most of the batches were high (>30% of calves with lung lesions = 42%) or medium (20-30% of calves with lung lesions = 50%) and only one (8%) was a low risk batch (<20% of lung lesions). Randomized selection of a percentage of calves following the sampling table was performed 10 times. The average results for these 10 randomizations were very similar to the real ones, and the estimated sensitivity was 96% for batches with at least a 30 % of prevalence of disease.
Conclusions
Thoracic US scanning of a randomized percentage of calves at arrival may be a useful technique to identify high-risk BRD batches where metaphylactic treatment is justified. This technique can be a practical tool for a more rational use of antibiotics in the veal industry.
Keywords: Feedlot, BRD, ultrasound, thoracic, calves.
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