Development of cyathostome infection of helminth‐naive foals

Summary Three groups of 5 Welsh‐Shetland crossbred pony foals each were infected with 450,000 third stage cyathostome larvae, given as either a single dose of freshly harvested larvae (Group A) or a single dose of larvae that had been cold conditioned for 6 weeks at 4°C (Group B) or as a trickle infection of 18 doses of 25,000 freshly harvested larvae administered on weekdays over 1 month (Group C). The mean pre‐patent periods of Groups A and B were 53 days with shortest and longest individual values of 48 and 62 days. In Group C the mean pre‐patent period was 65 days with a range from 60–77 days. The general patterns of faecal worm egg output were similar in Groups A and B, with rises in mean numbers of faecal worm eggs over about 3 weeks following patency, after which the mean worm egg counts in faeces remained between about 400 and 1,000 eggs/g. The mean faecal worm egg counts of Group C animals, at approximately 200–300 eggs/g, were lower than the mean values of Groups A and B. At post‐mortem examinations 16 weeks post infection, the group mean total and mucosal cyathostome worm counts were: Group A, 60,898–14,806; Group B, 33,592–13,292; Group C, 30,794–14,714. Therefore, the relative proportions of total worm burdens present at mucosal stages were different between groups with values of 24%, 39% and 49% for Groups A, B and C respectively. It was concluded that both larval chilling and trickle larval dosing influenced the development of experimental cyathostome infections.