[Part played by ectoparasites in the syndrome of sheep "on its back" (author's transl)].

After putting themselves on the back, many ewes die because they are not able to rise to their feet again. Severe itching seems to be the cause of this abnormal posture. A whole herd treatment against ectoparasites (HCH spray) has reduced by 80% the losses caused by this condition during the years 1964 to 1971 in about a hundred herds in the department of Saône-et-Loire. The persistency of a small number of cases in treated herds could be due to non-parasitic causes.