Abstract

Simple SummaryGrazing horses year-round may be a means to increase biodiversity. In this study, parasite occurrence was documented on a monthly basis in 1- to 3-year-old Gotlandsruss stallions grazed year-round for 2.5 years. Horses became infected by several parasites and, when needed (>200 strongyle eggs/gram feces), horses were dewormed with the anthelmintic drug pyrantel, which has low or no ecotoxic impact on soil fauna. This strategy failed to control small strongyle occurrence. Horses excreted larger amounts of small strongyle eggs during summer–autumn than during the rest of the year, and the number of excreted eggs increased year-on-year. High small strongyle egg excretion did not seem to affect the body condition of the horses. Some horses were also infested with chewing louse, but did not scratch more than unaffected horses. We found that to keep egg excretion below 200, pyrantel was not sufficient and a substance known to be toxic to dung fauna and freshwater invertebrates had to be used on some occasions.Horse grazing can be favorable from a biological diversity perspective. This study documented the occurrence of endo- and ectoparasites and sought to reduce parasite egg excretion with the anthelmintic drug pyrantel in 12 Gotlandsruss stallions maintained in a year-round grazing system for 2.5 years. Feces samples were collected monthly and all horses were treated with pyrantel, the anthelmintic drug of choice in biological diversity preservation, at study population mean cyathostomin eggs per gram (EPG) of >200. The relationship between cyathostomin EPG and body condition was studied, as was horse behavioral response to Bovicola equi (chewing louse) infestation. Eggs of cyathostomins (small strongyles), Parascaris spp. (roundworm), Oxyuris equi (pinworm), Anoplocephala perfoliata (tapeworm), and Gasterophilus spp. (botfly) were detected at least once during the trial. Excretion of cyathostomin eggs was highest during summer–autumn and increased year-on-year. No relationship was found between cyathostomin EPG and body condition. Infestation with B. equi did not affect the number of scratching sessions compared with unaffected horses. Therefore, in this year-round grazing system, pyrantel treatment had to be complemented with moxidectin to reduce excretion of cyathostomin eggs, thus compromising biological diversity.

Highlights

  • There is ongoing loss of biological diversity worldwide (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, 2019)

  • There was an individual effect on eggs per gram (EPG) (p < 0.1), with individual least square means (LSmeans) for the whole study period ranging from 58 to 365 EPG

  • We conclude that there was an effect of season on cyathostomin egg excretion by year-round grazing horses in this study, with two peaks observed every year

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Summary

Introduction

There is ongoing loss of biological diversity worldwide (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, 2019). This study was part of a 2.5-year project studying the effect of year-round grazing, without supplementary feeding, by horses on biological diversity and horse growth, health, and welfare. A recent publication from this project reports that horse grazing increases plant diversity and the presence of pollinators [2]. Year-round horse grazing, as tested in the project, can be recommended from a biological diversity perspective. To our knowledge, there have been no long-term studies on the occurrence of endo- and ectoparasites in such a system. A strategy to control endo- and ectoparasites is needed to keep grazing horses healthy and in functioning body condition, so that challenging weather and periodic feed shortages do not affect their health and welfare

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