The Course of Naturally Acquired Helminth Infections of Horses Given Regular Anthelmintic Treatment

Abstract

Summary Three groups of 3 pony foals were grazed together on old established pasture, heavily contaminated with strongyle larvae. Two groups were treated each month with thiabendazole at dosages of 50 mg./kg. and 240 mg./kg. and the third group was kept undosed as a control. During 2 years of monthly observations, the peripheral eosinophil counts were similar in each group, irrespective of the anthelmintic treatment given. Further, there appeared to be a rhythm in the eosinophil counts, higher counts being recorded in the summer months and lower counts during the winter months. It is suggested that the eosinophil counts reflect the degree of exposure to infection and the subsequent larval systemic migration. There was no correlation between the eosinophil counts and the adult worm egg-producing population in the lumen of the intestines. The serum β-globulins were high in all animals at the beginning of the experiment, but in the treated groups a marked reduction occurred.