Monitoring equine ascarid and cyathostomin parasites: Evaluating health parameters under different treatment regimens

Abstract

Background Strongylid and ascarid parasites are omnipresent in equine stud farms, and ever‐increasing levels of anthelmintic resistance are challenging the industry with finding more sustainable and yet effective parasite control programs. Objectives To evaluate egg count levels, bodyweight and equine health under defined parasite control protocols in foals and mares at two Standardbred and two Thoroughbred stud farms. Study design Longitudinal randomised field trial. Methods A total of 93 foals were enrolled and split into two treatment groups, and 99 mares were enrolled and assigned to three treatment groups. All horses underwent a health examination, and episodes of colic or diarrhoea were recorded at each faecal collection date. Bodyweights were assessed using a weight tape, and mares were body condition scored. Group A foals (FA) were dewormed at 2 and 5 months of age with a fenbendazole/ivermectin/praziquantel product, while group B foals (FB) were dewormed on a monthly basis, alternating between the above‐mentioned product and an oxfendazole/pyrantel embonate product. Group A mares (MA) were dewormed twice with fenbendazole/ivermectin/praziquantel, group B mares (MB) were dewormed with the same product, when egg counts exceeded 300 strongylid eggs per gram, and group C mares (MC) were dewormed every 2 months, alternating between the two products. Health data were collected monthly for 6 months (foals) and bimonthly for 13 months (mares). Data were analysed with mixed linear models and interpreted at the α = 0.05 significance level. Results There were no significant bodyweight differences between foal groups, but MA mares were significantly lighter than the other two groups. Very few health incidents were recorded. Foals in group FA had significantly higher ascarid and strongylid egg counts, whereas no significant differences were observed between mare groups. Main limitations Study duration limited to one season. Conclusions Anthelmintic treatment intensity was lowered from the traditional intensive regimes without measurable negative health consequences for mares and foals.

Parasite dynamics in untreated horses through one calendar year

“…Our results demonstrate a lack of seasonal differences in strongylid egg shedding among the mature horses. As outlined in the introduction, this is in stark contrast to both historical and more recent studies, which collectively demonstrated clear seasonal differences [ 11 , 18 – 22 ]. However, as mentioned previously, most of these previous studies were conducted in the UK, and since very few studies have been completed elsewhere, these patterns may differ substantially between regions and climates.…”

“…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 ].…”

The equine ascarids: resuscitating historic model organisms for modern purposes

“…Poor body condition has been associated with Parascaris spp. infection in working equids (Getachew et al 2008 , 2010 ); however, foals under parasite management programs have not exhibited these signs in recent studies (Bellaw et al 2016 ; Nielsen et al 2021 ). Small intestine impaction is one of the largest concerns with this parasite, often requiring hospitalization and surgery, and can ultimately lead to death (Nielsen 2016 ; Southwood et al 1996 ; Cribb et al 2006 ; Tatz et al 2012 ).…”

Helminths and their management in Swiss Army horses: differences between riding horses and pack horses evidence the need of improvement

“…48 In relation to prevalence and abundance, non-migratory small strongyles play the main role in horses in western Europe and most other regions of the world. 6,37,39 This group of parasites (also called cyathostomins and comprehending approximately 50 species) 26 is clinically relevant in case of larval cyathostominosis, induced by sudden eruption of encysted larvae into the intestinal lumen. This is a syndrome that occurs mostly seasonally in late winter or spring.…”