EXPERIMENTAL OESOPHAGOSTOMUM-DENTATUM INFECTIONS IN THE PIG - WORM POPULATIONS AT REGULAR INTERVALS DURING TRICKLE INFECTIONS WITH 3 DOSE LEVELS OF LARVAE

A trickle infection experiment was undertaken to study in detail the p opulation dynamics of Oesophagostomum dentatum in pigs. Three groups o f 32 pigs were inoculated via the feed twice weekly with 100 (Group A) , 1000 (Group B) or 10000 (Group C) O. dentatum infective larvae (L-3) . Five pigs from each group were killed 2, 4, 8, 12, 16, and 20 weeks after the first inoculation (p.i.) to determine their worm burdens. We ekly faecal egg counts were determined. At slaughter, worms were count ed, differentiated according to sex and developmental stage, and their length measured. Faecal egg counts ranked with dose rate until week 1 5, but later were more variable. The proportion of the total number of L, administered which were recovered at slaughter inversely ranked wi th dose rate. In group C it decreased over time, whereas in groups A a nd B there was no consistent pattern. Worm fecundities (epg/female) in groups A and B were higher than in group C. The lengths of the female worms increased over time, whereas the lengths of the male worms rema ined approximately constant from week 8. The study suggests reduced es tablishment of incoming larvae and lower fecundity of the female worms at high dose levels.