Seasonal changes and inhibited development of the abomasal nematodes of sheep and goats in Saudi Arabia.

From August 1991 to July 1992, a total of 48 abomasa from sheep and 48 from goats were examined at the Jeddah abattoir for the presence of adult and larval nematodes. Twenty-three of the sheep (47.9%) and 21 of the goats (43.8%) were infected with nematodes, a total of eight species being found. Haemonchus contortus and Marshallagia marshalli appeared to be the most important parasites. Other species were less prevalent: Trichostrongylus axei, Camelostrongylus mentulatus, Parabronema skrjabini, Ostertagia circumcincta, Skrjabinagia lyrata, Ostertagia trifurcata. Overall worm counts and infection rates were lowest in the winter. Larval inhibition plays an important role in the Marshallagia life cycle, since this parasite survives the dry season as arrested larvae. By contrast, inhibition of Haemonchus was less pronounced and the parasite survived the same season as adults and larvae. Although the phenomenon of hypobiosis was observed, the number of inhibited larvae was too small to be expected to induce clinical symptoms after resumption of development.