A recent research study was published in the Equine Veterinary Journal by Dr. Martin Nielsen and colleagues titled, "Monitoring equine ascarid and cyathostomin parasites: Evaluating health parameters under different treatment regimens." Co-authors were Gee, E.K.; Hansen, A.; Waghorn, T.; Bell, J.; and Leathwick, D.M.
This longitudinal randomized field trial evaluated egg count levels, bodyweight and equine health under defined parasite control protocols in foals and mares at four stud farms in New Zealand.
Foals (n = 93) were divided into two treatment groups; group A was dewormed at 2 and 5 months of age with a fenbendazole/ivermectin/praziquantel product, while group B was dewormed monthly, alternating between the above-mentioned product and an oxfendazole/pyrantel embonate product.
Mares (n = 99) were divided into three groups; group A was dewormed twice (early summer and winter) with fenbendazole/ivermectin/praziquantel, group B was dewormed with the same product only when egg counts exceeded 300 eggs per gram, and group C was dewormed every 2 months, alternating between the two products. Health data was collected at two-monthly intervals for a total of 13 months.
Foals in group A had significantly higher ascarid and strongylid fecal egg counts compared to group B, but no significant differences were observed between mare groups. There were no differences between groups with regard to body weight and body condition score. One foal in group B developed diarrhea during the monitoring period. No colic signs were reported in any group during the study.
Bottom line: Reducing anthelmintic treatment intensity can lead to higher ascarid and strongylid egg counts in foals on stud farms; however, no negative health consequences were observed within the timeframe of this study. Longer monitoring periods are needed to assess the effects of increased egg shedding on subsequent foal crops.