Summer-arrested development of abomasal trichostrongylids in Awassi sheep in semi-arid areas of north-west Syria.

Inhibition in trichostrongylids was studied in Awassi sheep in North-west Syria, which has cold winters and hot summers. On six occasions during a 1-year period, five ewes with natural helminth infections were slaughtered after being held in pens for 3 weeks. The percentage of inhibited larvae was lowest in January (6%); it increased during the spring to 76.7% in April and to 84.6% in June and then decreased during the autumn (57.1% in September, 26.1% in December). Inhibition occurred mainly during the early fourth stage in mucosa but was also observed during the late fourth stage in digesta. Teladorsagia circumcincta was the main species involved, but it seemed that this phenomenon also occurred in Marshallagia marshalli.