Economic assessment of FEC-based targeted selective drenching in horses

In the face of an increased prevalence of drug-resistant cyathostomin populations, a targeted selective treatment (TST) strategy based on Faecal Egg Counts (FECs) has been proposed as an alternative management strategy. However, associated costs may be a barrier to the uptake of this strategy. Our study aims to provide an economic assessment of FEC-based TST. FECs were determined in a Welsh pony herd thrice a year from 2010 to 2014. This database was used to explore the impact of FEC price, sampling strategy (individual or pooled) and labour-associated costs. Drug price was set at the cheapest level, hence providing a conservative framework to determine the maximum viable FEC price in the context of a cost-driven horse industry. The maximum viable FEC price for a cost-efficient individual based strategy was determined by an in silico bootstrap approach consisting of randomly sampling 1000 virtual pony herds of various sizes (1 to 100 ponies) from the available database and estimating the associated costs (FEC price ranging from € 1 to € 10, anthelmintic costs and labour-associated costs). The costs and benefits of the pooling strategy that consists of basing the decision to treat on group FEC values were also investigated. This is thought to reduce FEC-based costs but may result in highly infected individuals being left undrenched, i.e. in false-negatives, as a result of FEC overdispersion. For various pool-sizes (1-20 ponies) and various cut-off thresholds (50-200 eggs/g), we sampled 1000 pony herds in silico to estimate the associated costs and determine the number of positive ponies within a negative pool. Following these simulations, pool-based FECs of various sizes were performed on 40 ponies to compare predictions with real data. Within 4 years, anthelmintic costs were cut by 80%, albeit with free FECs. In silico estimations suggested that an individual FEC-based TST would not be cost-efficient in this context for an FEC price above € 5. With a pooled FEC strategy, the proportion of false-negatives never exceeded 15% of the pool size. The combination of a 14-pony pool and a cut-off value of 150 eggs/g minimized total costs while keeping the number of false negatives to a reasonable level. Real data obtained from infected ponies however, suggested that pool size should not exceed 10 individuals, since the inhomogeneous mixing of faeces of larger pools probably reduced the correlation between average pooled FECs and the mean of individual FECs. Our study provides an economic framework that could be valuable for emphasizing the use of FEC-based approaches in the field.