Authors

Discussion

Increasing levels of anthelmintic resistance has led to amplified interest in alternative control methods for gastrointestinal nematode infections of livestock. One method is using alternative feed stuffs such as tree leaves. These can induce a displacement effect by reducing consumption of contaminated pasture, and may also contain secondary metabolites, such as condensed tannins, with anthelmintic properties. However, these are limited resources and cannot be fed year-round, so optimisation of the timing of use is critical. This study uses mathematical modelling to predict the effect of these treatments at different times of year on GIN epidemiology. The GLOWORM-FL model framework was extended to include parasitic stages of the lifecycle to facilitate modelling the effects of tannins on different lifecycle parameters. Parameter values were calculated based on effect sizes reported in published in vivo and in vitro studies of tree leaf tannins on GINs. The model was run across four different locations along a north-south gradient across western Europe, and for 52 individual years (1970 – 2022) in each location to determine spatial and temporal variations. The effects of tannin-rich and no tannin forages are compared. Across all locations, the effect of displacement on adult worm burden is highest at the start of the year and gradually decreases throughout. The effect of tannin-rich fodder has a different seasonal pattern with the greatest level of effect occurring during the rise in adult parasite numbers, but before the peak. This therefore differs between species, location, and year to different degrees. These findings support the use of model optimisation of treatments to gain maximum benefit and the framework developed here can also be applied to the use of many different treatment strategies.