Abstract
The objective of this study was to use probabilistic sensitivity analysis to evaluate the cost-effectiveness of using an on-farm culture (OFC) approach to the treatment of clinical mastitis in dairy cows and compare this to a ‘standard’ treatment approach. A specific aim was to identify the herd circumstances under which an OFC approach would be most likely to be cost-effective. A stochastic Monte Carlo model was developed to simulate 5000 cases of clinical mastitis at the cow level and to calculate the associated costs simultaneously when treated according to 2 different treatment protocols; i) a 'conventional' approach (3 tubes of intramammary antibiotic) and ii) an OFC programme, whereby cows are treated according to the results of OFC. Model parameters were taken from recent peer reviewed literature on the use of OFC prior to treatment of clinical mastitis. Spearman rank correlation coefficients were used to evaluate the relationships between model input values and the estimated difference in cost between the standard and OFC treatment protocols. The simulation analyses revealed that both the difference in the bacteriological cure rate due to a delay in treatment when using OFC and the proportion of Gram-positive cases that occur on a dairy unit would have a fundamental impact on whether OFC would be cost-effective. The results of this study illustrated that an OFC approach for the treatment of clinical mastitis would probably not be cost-effective in many circumstances, in particular, not those in which Gram-positive pathogens were responsible for more than 20% of all clinical cases. The results highlight an ethical dilemma surrounding reduced use of antimicrobials for clinical mastitis since it may be associated with financial losses and poorer cow welfare in many instances.
Highlights
Mastitis is one of the most prevalent and costly diseases affecting dairy cows worldwide
The purpose of this research was to use probabilistic sensitivity analysis to investigate the main factors that influence the costeffectiveness of an OFC approach to treating clinical mastitis
There has undoubtedly been a shift in the aetiology of clinical mastitis towards environmental pathogens, with coliforms and no-growths frequently reported as accounting for approximately 50% of all clinical mastitis culture results (Bradley and Green, 2001; Bradley et al, 2007; Breen et al, 2009) as was the case in the study by Lago et al (2011a)
Summary
Mastitis is one of the most prevalent and costly diseases affecting dairy cows worldwide. While OFC appears to be effective in reducing antimicrobial drug usage; little is known about factors influencing the overall costeffectiveness of this approach and, the types of herds in which it is most likely to be cost-effective When performing such a cost-effectiveness analysis, there are inevitably multiple sources of evidence for parameter estimates and a degree of uncertainty surrounding their true value (Ades et al, 2006). For decision-making purposes, it is important that cost-effectiveness models are able to incorporate multiple sources of evidence and reflect uncertainty in the model outputs (Claxton et al, 2005; Babo Martins and Rushton, 2014) An approach to this widely reported in the human health literature (Briggs et al, 2002; Brown et al, 2006) and increasingly in the veterinary literature (Down et al, 2013; Hudson et al, 2014, 2015) is probabilistic sensitivity analysis (PSA). This parameter uncertainty is propagated through the cost-effectiveness model so that the resulting imprecision is reflected in model outputs and inferences made (Briggs et al, 2002)
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