Parasites in Horses Kept in A 2.5 Year-Round Grazing System in Nordic Conditions without Supplementary Feeding

Abstract

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.

Effect of Vegetable Oils Feed Additives on Endoparasites Associated with Dewormed Racing Horses

“…Repeatable observations of relatively high amounts of strongyle ova in feces of regularly dewormed animals may result, in addition to the aforementioned cessation of biological activity of ivermectin, from the development of the drug-resistance in representatives of Strongylidae. The latter, in turn, may be an outcome of incorrect use of the named anthelmintics [10,12]. This assumption is partly supported by already cited results by Kuzmina et al [38], who revealed that a statistically significant difference in EPG values was present only between horses with rare to lack of anthelmintic treatments but not between horses dewormed 1-2 a year vs. 3-4 times or more with macrocyclic lactones.…”

“…This procedure only temporarily reduces the number of adult parasites susceptible to the drug used [3]. The latter, combined with a recurrent application of the same and/or close pharmacological agents, with ivermectin and praziquantel being most commonly used [4][5][6] leads to partial or complete resistance developed by many parasites, especially gastro-intestinal, which cannot be eradicated with these drugs anymore [7][8][9][10][11][12]. The parasites that have become or have been gradually becoming resistant to currently used preparations are representatives Agriculture 2021, 11, 525 2 of 13 of Ascarididae, Strongylinae, Cyathostominae, Anoplocephalids and botflies from Gasterophilus spp.…”

Parasite dynamics in untreated horses through one calendar year

“…In the past decade two British studies have been published, with one finding similar seasonal egg shedding patterns [ 19 ], while the other found no evidence of such seasonality among adult horses [ 20 ]. Recently, a Swedish 2.5-year study of free-ranging ponies found strongylid fecal egg counts (FECs) to peak in August/September [ 21 ], and a New Zealand study reported broodmares to exhibit lower strongylid FECs during winter months [ 22 ], both confirming Poynter’s observations from almost 70 years ago. One study performed in ponies in Louisiana, USA, reported significantly lower mean strongylid FECs during winter months, but these were data from ponies that were euthanized at different time points, and repeated measures were not done across seasons [ 23 ].…”

Experimental rewilding may restore abandoned wood-pastures if policy allows

“…During the study period, four individuals were temporarily removed due to low body condition in late winter. They were additionally dewormed when necessary using predefined indicators (Tydén et al 2019 ) and were provided with artificial shelter and water in troughs (one per enclosure according to national regulations). From January 2016, one horse was excluded from the study due to injury.…”