Quantitative and qualitative analysis of antimicrobial usage in white veal calves in France

The development of antimicrobial resistance has made it necessary to measure antimicrobial usage in animal production sectors. France is a major European producer of white veal calves, but few data were previously available for that sector, even though these young animals are particularly susceptible to infection and considered as a reservoir of antimicrobial resistance. A cross-sectional study was conducted on 186 batches of French calves to estimate the exposure of white veal calves to antimicrobials and identify the potential risk factors related to antimicrobial usage. An indicator of calf exposure was calculated as a count of the number of antimicrobial treatments per calf. The indicator was based on veterinary prescriptions (products, quantity dispensed and dosage prescribed) and the estimated weight of calves at treatment, using the dates of treatment collected from farm registers. The study showed that calves were exposed to an average of 8.55 antimicrobial treatments (SD: 2.21, range: 2.75-15.86) over the five to six months of the fattening process. Group treatments were predominant (95.8%) and administered by the oral route. The "starting treatments", given during the first two weeks of the fattening period, were administered systematically (to all the calves in all the farms) and accounted for a third of all treatments. Tetracyclines, polypeptides and macrolides were the most widely used antimicrobials, with respectively 4.32, 1.59 and 1.01 treatments per calf. Only rare uses of 3rd and 4th generation cephalosporins and fluoroquinolones, considered as critically important in human medicine, were reported. Despite low variability of exposure between farms, a linear mixed-effects model highlighted a higher variability between farmers (ICC=0.14) or veterinarians (ICC=0.12), than between integrators (ICC=0.06). The number of calves per pen, introduced as a fixed effect in the model, was also significant: calves housed in pens of 6-10 and fed in buckets had on average 2.55 more antimicrobial treatments per calf than calves housed in pairs with the same feeding system. The model also highlighted an increase of 1.48 treatments per calf for farms with more than five percent of mortality, versus those with two percent or less. The present study showed that antimicrobial treatments are numerous in veal calf fattening farms, particularly at the arrival of the animals. Taking into account the development of resistance to antimicrobials, the necessity and the effectiveness of some of these treatments should be re-evaluated.