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Changes in the prevalence of intestinal worms in a mixed flock of donkeys and horses treated with ivermectin
Skultéti Enikő Mónika - year 6
University of Veterinary Medicine Budapest, Department of Parasitology and Zoology
Supervisors: Dr. Gábor Majoros, Dr. Alexandra Juhász


The presence of intestinal helminths of horses and donkeys kept on common pasture was investigated to determine if the amount of parasites in the two host species shows any difference that can be detected by routine faecal examination. Previously, the keeping, feeding and schedule of treating the animals which were investigated by us, was independent of the actual worm infestation of the animals, and was carried out entirely upon the decision of the owner. Accordingly, anthelmintic treatments have been performed, either routinely, at certain intervals or occasions, or when the animals had symptoms which were suspected infestation by intestinal worms (such as diarrhoea, thinning). Animals arriving at the livestock farm were dewormed and then they were treated by drugs against worms quarterly. In case of adult animals, ivermectin-containing formulations were administered orally, and fenbendazole was given to foals less than six months of age. The number of animals and their ages in the herd had been constantly changing, so although we have always tried to take sample the same animals that we were selected previously, for the sake of comparison we also took samples from the new horses in the herd, from the mares before calving and the donkeys of poorer general condition.

During the investigations we found mainly strongylid eggs and in some cases also roundworm (Parascaris equorum) and pinworm (Oxyuris equi) eggs. In case of the donkeys, just one or two months after the application of dewormer, strongylid eggs have been found in their droppings. However, not only less amount of eggs were found initially in the faeces of horses, than in donkeys but their faeces have been free of eggs for up to 10 months after the deworming treatment. Both ivermectin and fenbendazole treatment resulted expelling the worms, however, after the treatment with fenbendazole, the shedding of strongylid eggs continued, which seems to prove that the efficacy of this drug is decreasing.

Because horses and donkeys were kept together in the same way at the same place, the differences in infection rates between the two animal species is probably due to differences in their behaviour, feeding habits and perhaps by different tolerances to parasites. The absence of eggs in faecal samples for months after treatments has shown that compared to that of blind therapy, the frequency of applications of highly efficient drugs can be substantially reduced if the result of the treatment always controlled by faecal examination. This schedule also reduces the chance of parasites to develop a resistance to antiparasitic drugs.

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