The effect of three distinct sex ratios at two Oesophagostomum dentatum worm population densities.

Helminth-free donor pigs were inoculated with infective larvae of Oesophagostomum dentatum. Five weeks later, the donor pigs were killed to recover the adult worms. By nonsurgical rectal transplantation, 6 groups of helminth-free recipient pigs were then given different female-to-male ratios (FMR) of O. dentatum worms (10% females [F], 50% F, 90% F) at either high (300 worms) or low (30 worms) doses. Fecal egg excretions were measured once weekly following transplantation until the pigs were killed 4 wk posttransplantation to assess the worm burdens and their location. There was a strong and significant correlation between numbers of male and female worms located in the different sections of the large intestine, suggesting that the worm sex as well as physiological factors in the pig intestine may govern the location of the worms. There were no significant differences in fecal egg counts or female worm fecundity between any of the groups. However at the low dose level, the female worm fecundity was markedly lower in the L10% F group than in the 2 other groups, thus suggesting for low worm densities an upper threshold for the FMR above which O. dentatum females produce fewer eggs.