Seasonally inhibited development of cyathostomine nematodes in Shetland ponies in The Netherlands.

Two groups of three yearling Shetland ponies were used in 1988 to study the epidemiological significance of inhibited development of the Cyathostomine nematodes. In Group 1, acquisition of infections was prevented throughout the grazing season whereas in Group 2 strongylid infections were acquired from the beginning of July until the end of September. Worm counts showed that the Cyathostomine nematode populations of Group 1 ponies mainly consisted of adult worms and those of Group 2 ponies of inhibited early third stage larvae (L3). These results indicate that a large proportion of Cyathostomine larvae which establish between the beginning of July and the end of September inhibit their development. The results also suggest that the pool of inhibited larvae which has overwintered in young ponies will be depleted in autumn.