Big reductions in the number of anthelmintic doses given to horses can be made by employing an evidence-based deworming programme, researchers report.
Liselore Roelfstra, Marion Quartier and Kurt Pfister, writing in the journal Animals, looked at the results of deworming practices on five riding horse farms in France and Switzerland.
About six years ago, in the autumn of 2014, all had switched to an evidence-based treatment system for small strongyles based on the results of fecal egg counts.
Each animal was tested twice a year, in spring and autumn. A dewormer was given only if the egg count was found to be 200 eggs per gram or more.
The study encompassed 90 horses and three ponies, ranging in age from 3 to 32.
The five farms were primarily riding stables with a paddock pasture system. There was no regular collection of feces from the pasture on three of the farms, whereas the other two collected at least once a week.
Over the six years, a total of 757 fecal samples underwent testing.
Of all samples analyzed, only 34.7% had an egg count of 200 or more, resulting in a dewormer treatment.
This meant that 263 doses were administered over the six years, compared to the 757 treatments that would have been systematically given to all these horses as was routinely done at least twice a year during the six years before the new programme was introduced.
Indeed, all the horses in the study were regularly treated two or three times a year without fecal egg counts in the years before the new programme.
The small number of fecal samples over 200 eggs per gram showed the considerable potential for a long-term reduction in the number of anthelmintic treatments and anthelmintic pressure by using an evidence-based system, the study team said.
The overall reduction of the number of anthelmintic treatments across the five farms was 65.3%.
“On four out of the five farms, these reductions were much more marked and showed very low variations when comparing their results,” they said.
A reduction in the treatment number of only 35% occurred on one of the farms. “The reasons were unknown, but this farm — set up more recently — had quite a frequent turnover of horses (and horse owners).”
Roelfstra and her fellow researchers said the findings showed that conducting eggs counts twice a year on horses is easily feasible in riding farms with several horse owners, and with animals coming and going.
“Undoubtedly, a major condition for a successful implementation of such a control scheme is the positive consent of the farm owner or manager.
“However, this field study clearly demonstrates that many horse owners — all owners in this study had to pay for the analyses — are prepared to pay for such well-driven parasite control, despite some economic concern about the laboratory costs for fecal analyses.”
Parasite control involving laboratory fecal analysis is reasonably adaptable and mostly successful, they said.
“An additional advantage is that any kind of anthelmintic treatment can be made in a parasite-specific way according to the detected parasite spectrum.”
The findings, they said, are of particular importance in terms of slowing the development of drug resistance among parasites.
“The achieved overall reduction clearly shows the potential for a reduction of the number of anthelmintic treatments on horse riding farms when appropriately done.”
The authors, all with the Animal Diagnostic Laboratory in Corcelles-Cormondrech, Switzerland, also noted that there was not a single report of another parasite-associated disease problem on any of the farms for the entire study period.
“However … any monitoring procedure should regularly include a reliable detection method for Strongylus vulgaris in order not to miss the re-emerging of this highly pathogenic helminth.”
Roelfstra, L.; Quartier, M.; Pfister, K. Preliminary Data from Six Years of Selective Anthelmintic Treatment on Five Horse Farms in France and Switzerland. Animals 2020, 10, 2395.