Can fenbendazole-medicated molasses blocks control Toxocara vitulorum in smallholder cattle and buffalo calves in developing countries? Studies from upland Lao PDR

Context Anthelmintic treatments are not widely adopted by smallholder farmers in Laos (Lao People’s Democratic Republic) to treat bovid Toxocara vitulorum, resulting in high calf morbidity and mortality. Aims Field trials were conducted to provide baseline efficacy data on an alternative, easy-to-use treatment by provision of fenbendazole-medicated molasses blocks (FMB) in situ. Methods Participating villages were randomly allocated to the following treatments: (1) conventional orally administered pyrantel, (2) access to FMB, (3) access to non-medicated molasses blocks (MB), and (4) no blocks (control). Faecal eggs per gram (EPG) and weight were monitored in cattle (n = 171) and buffalo calves (n = 44) under field conditions for 48–56 days. Key results In 2016, the MB treatment was associated with the fastest reduction in predicted average EPG at 2% per day, while FMB and pyrantel had an equivalent reduction of 1% per day, relative to the control (P = 0.062). Predicted average weight also differed significantly among treatments, with pyrantel and MB having the greatest average daily gain at 230 g and FMB at 200 g, which was higher than for control calves at 170 g (P = 0.002). In buffalo calves, treatment was not significantly associated with EPG or weight. The 2018 trial corroborated that FMB and MB treatments were associated with increased EPG reductions in cattle at 3% per day, relative to control calves (P = 0.007). Again, the MB treatment had the greatest predicted average daily gain at 200 g, compared with FMB calves at 160 g and control calves at 150 g (P = 0.005). Conclusions The field trials provided baseline evidence that FMB and MB have potential applications in reducing environmental contamination of T. vitulorum eggs and may improve calf growth in low-input systems. However, further testing ex situ is required to control for variability in calf weight and T. vitulorum burdens, so as to optimise anthelmintic doses, assess the addition of urea to the block formula and assess product marketability. Implications If successful, medicated nutrient blocks may be a simple method to reduce calf mortality and morbidity, enhancing the reproductive efficiency of large ruminant production in smallholder farms in developing countries.