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

Abstract

<p><i><b>Context.</b></i> Anthelmintic treatments are not widely adopted by smallholder farmers in Laos (Lao People’s Democratic Republic) to treat bovid <i>Toxocara vitulorum</i>, resulting in high calf morbidity and mortality.</p> <p><i><b>Aims.</b></i> Field trials were conducted to provide baseline efficacy data on an alternative, easy-to-use treatment by provision of fenbendazole-medicated molasses blocks (FMB) <i>in situ</i>.</p> <p><i><b>Methods.</b></i> 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 (<i>n =</i> 171) and buffalo calves (<i>n =</i> 44) under field conditions for 48–56 days.</p> <p><i><b>Key results.</b></i> 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 (<i>P =</i> 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 (<i>P =</i> 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 (<i>P =</i> 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 (<i>P =</i> 0.005).</p> <p><i><b>Conclusions.</b></i> The field trials provided baseline evidence that FMB and MB have potential applications in reducing environmental contamination of <i>T. vitulorum</i> eggs and may improve calf growth in low-input systems. However, further testing <i>ex situ</i> is required to control for variability in calf weight and <i>T. vitulorum</i> burdens, so as to optimise anthelmintic doses, assess the addition of urea to the block formula and assess product marketability.</p> <p><i><b>Implications.</b></i> 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.</p>