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- Title
Visual weight estimation and the risk of underdosing dairy cattle.
- Authors
van Dijk, J.; Eagle, S. J.; Gillespie, A. V.; Smith, R. F.; Holman, A. N.; Williams, H. J.
- Abstract
Context Drug resistance is a serious threat to human health, food security and the livelihood of livestock farmers. As vets and farmers routinely calculate drug volumes from weight estimates based on visual inspection of cows, an associated risk of underdosing may contribute to the build up of resistance. This study investigated administrator-induced error in the delivery of optimal doses of drugs to dairy cattle. Main conclusion Dairy cows were much heavier than observers thought. Vets were highly likely to underestimate the weight of ≥650 kg animals and dairy farmers underestimated the weight of cows significantly more than vets. Approach Seventeen cattle vets (median experience 10 years) and 18 dairy farmers (median experience 22 years) were asked to estimate the weight of seven cows (actual weights 580 kg, 624 kg, 638 kg, 694 kg, 728 kg, 740 kg and 808 kg). The weight of the 638 kg cow was then revealed and the observers were asked to rescore the other six cows. Logistic regression (on the probability of underestimating weight) and multiple linear regression (on the difference between estimated and measured weight) were carried out using the covariates 'vet or farmer', 'actual cow weight', 'knowing the weight of one of the cows' and 'years of experience of the observer'. Results Of the veterinary observations made, 64.7 per cent were underestimations of the weight of cows (mean underestimation 63 kg, maximum 248 kg), whereas 80.9 per cent of farmer observations were underestimations (mean underestimate 97 kg, maximum 233 kg). The likelihood and degree of underestimation increased significantly with the weight of the cow observed. Accuracy of weight estimation increased significantly after the weight of one animal was revealed. Farmers were 2.34 times more likely to underestimate weight than vets. Observer experience did not appear to have an effect on weight estimation accuracy. Interpretation The probability of non-weighed dairy cows receiving too low a drug dose is high and, in heavier animals, the degree of underdosing may be substantial. The degree to which this contributes to the development of drug resistance needs further investigation. Significance of findings Farmers administer the vast majority of drug doses and currently employed weight estimation methodology may contribute to the development of drug resistance. Practicable improvements on current methods need to be developed and training needs to be provided.
- Subjects
BODY weight; DRUG dosage; DAIRY cattle; VETERINARY medicine; DRUG resistance; LOGISTIC regression analysis
- Publication
Veterinary Record: Journal of the British Veterinary Association, 2015, Vol 177, Issue 3, p75
- ISSN
0042-4900
- Publication type
Article
- DOI
10.1136/vr.102955