DRUG-ABBREVIATED INFECTIONS AND DEVELOPMENT OF IMMUNITY AGAINST TRICHOSTRONGYLUS-COLUBRIFORMIS IN SHEEP

A protective immune response without liveweight loss can be induced in sheep against T. colubriformis but results depend on the anthelmintic used and duration of immunizing infections. More than 90% protection was achieved in sheep immunized by three 15- or 7-day oxfendozole abbr eviated infections or three 21-day nonabbreviated infections. Only 41% protection was induced by 3-day oxfendozole abbreviated infections. S ignificantly higher worm burden and faecal egg counts were present aft er challenge in sheep immunized by 7-day levamizole abbreviated infect ions compared to 7-day oxfendazole abbreviated infection. Liveweight g ains of sheep immunized by 15- and 7-day abbreviated infections sere n ot significantly different than non infected controls. Liveweight loss seemed to be associated with high activity of mucus peroxidase and hi gh numbers of eosinophils in the intestinal lumen. High parasite numbe rs seemed to be associated with low activity of alkaline phosphatase i n mucus. Mucus peroxidase, arylsulphatase, larval migration inhibition of mucus, mucus or serum antibody against L(3) excretory/secretory an tigen or somatic L(3), L(4) and adult antigen were not associated with protection.