Equine Cyathostominae can develop to infective third-stage larvae on straw bedding

Sandy Love, Faith A. Burden, Eoghan C. McGirr, Louise Gordon, Matthew J. Denwood

Domesticated grazing animals including horses and donkeys are frequently housed using deep litter bedding systems, where it is commonly presumed that there is no risk of infection from the nematodes that are associated with grazing at pasture. We use two different approaches to test whether equids could become infected with cyathostomines from the ingestion of deep litter straw bedding. Two herbage plot studies were performed in horticultural incubators set up to simulate three straw bedding scenarios and one grass turf positive control. Faeces were placed on 16 plots, and larval recoveries performed on samples of straw/grass substrate over 2- to 3-week periods. Within each incubator, a thermostat was set to maintain an environmental temperature of approximately 10 °C to 20 °C. To provide further validation, 24 samples of straw bedding were collected over an 8-week period from six barns in which a large number of donkeys were housed in a deep litter straw bedding system. These samples were collected from the superficial bedding at 16 sites along a "W" route through each barn. No infective larvae were recovered from any of the plots containing dry straw. However, infective cyathostomine larvae were first detected on day 8 from plots containing moist straw. In the straw bedding study, cyathostomine larvae were detected in 18 of the 24 samples. Additionally, in the two barns which were sampled serially, the level of larval infectivity generally increased from week to week, except when the straw bedding was removed and replaced. We have demonstrated that equine cyathostomines can develop to infective larvae on moist straw bedding. It is therefore possible for a horse or donkey bedded in deep litter straw to become infected by ingesting the contaminated straw. This has implications for parasite control in stabled equids and potentially in housed ruminants, and further investigation is required in order to establish the relative infective pressure from pasture versus straw bedding.