Factors influencing antimicrobial prescribing by veterinarians and usage by dairy farmers in New Zealand

AIMS: To determine the factors associated with the selection of antimicrobials by dairy veterinarians, and the attitudes of those veterinarians and dairy farmers to antimicrobial usage and resistance.METHODS: Facilitated focus groups of dairy farmers (n=22) and an anonymous online survey of dairy cattle veterinarians (n=206 respondents) were used to determine prescribing behaviour, factors affecting prescribing of antimicrobials, and the attitudes of veterinarians and farmers to the use of antimicrobials and the risk of antimicrobial resistance (AMR).RESULTS: Amongst the 22 farmers, the most common primary reason for choosing an antimicrobial was veterinary advice (87%) followed by personal experience (68%). Farmers had limited knowledge or concern about the risk of AMR, particularly outside their farm, with only 47% and 26% agreeing or strongly agreeing that use of antimicrobials on their farm would increase the risk of resistance in their herd and in humans, respectively.Prescribing of antimicrobials by veterinarians was predominantly based on diagnosis (168/206; 82%), and response to previous therapy (134/206; 65%), while duration above the minimum inhibitory concentration (43/206; 21%) was also considered important. Non-clinical factors such as withholding period (52/206; 25%) and farmers' preferences (45/206; 22%) also influenced prescribing. Antimicrobial culture and susceptibility testing was not widely used, with 126/166 (76%) having culture results for less than four of the last 10 clinical mastitis cases for which they prescribed antimicrobials. Attitudes about prescribing and AMR varied with years of practice, gender and employment status.CONCLUSIONS: Veterinarians primarily considered technical reasons when prescribing antimicrobials. However non-technical factors did influence prescribing, in particular client feedback about perceived efficacy and perceptions of cost/benefit. Farmers stated that veterinarians were the most credible source of advice for selection of antimicrobials, but that personal experience on their farm was also important.CLINICAL RELEVANCE: Farmers' perception of efficacy of antimicrobials, based on clinical outcomes, is an important determinant of their preferred choice of product. Hence, where changes in on-farm use patterns are required, clear communication by veterinarians about prudent antimicrobial choice and usage will require initial education around classes of antimicrobials and risk of resistance, as well as information around assessing efficacy of antimicrobial usage. Many veterinarians are in businesses that do not have practice prescribing policies. Such policies would likely lead to more consistent and judicious use of antimicrobials.