Quantification of antimicrobial usage in dairy cows and preweaned calves in Argentina

Antimicrobials are commonly used to treat diseases in dairy cows and in calves. In Argentina information about veterinary antimicrobial usage at herd level is still limited. The purpose of this study was to quantify antimicrobial usage at herd level of most used drugs to treat lactating cows (LC) and preweaned calves (PWC). Prevalence of diseases and antimicrobial drug usage in 18 milking herds and in 11 calves rearing units (CRUs) were assessed through a survey. Drug usage (DU) at herd level was estimated through a standardized indicator, the number of Defined Daily Doses Animal (DDDA) per year, considering a standardized body weight of 600kg for LC and of 60kg for PWC. Pearson correlation coefficients were estimated and used to evaluate the association of LC herd size and milk yield (kg/day) with each disease prevalence and with DU. Student t-Test was used to compare disease prevalence and DU with various management practices in CRUs. Clinical mastitis was the most prevalent disease followed by foot, uterine and respiratory diseases in adult dairy cows. More involvement of veterinarians in treatment decisions was observed in larger dairy herds. Most used antimicrobials were beta-lactams and aminoglycosides. Especially for intramammary compounds, there was a trend towards multidrug formulations. The median DU was 5.21 DDDA/LC/year (range=2.88-10.88), the intramammary usage for clinical mastitis (IM-CM) and dry cow therapy (IM-DRY), representing 85.4% of total drug usage. No significant correlations were observed between herd size or milk yield with disease prevalence and with DU for all considered uses (IM-CM, IM-DRY and parental (PAR)). Enteritis was reported in all CRUs, followed by respiratory disease (91%), and omphalophlebitis (3%). The median DU for all drugs used at CRU level was 0.49 DDDA/PWC/year. Prevalences and DU for treatment of enteritis and respiratory diseases did not differ significantly between rearing systems, colostrum management or permanence time of the calf with the mother after birth. Although it was possible to estimate the drug usage at farm level, it was observed that the diversity of drug compounds and dose heterogeneity presented by the various manufacturers made the calculation of those indicators complex.