Immunization of sheep against Haemonchus contortus: effect of vaccination on weight gain of animals and pasture contamination by infective larvae

Abstract

This study will be carried out to assess the degree of contamination of herbage with third-stage larvae (L3) of gastrointestinal nematodes and weight gain of sheep and lambs after immunization with gut membrane proteins from H. contortus. Thirty three ewes of Bergamacia breed will be utilized and distributed in three experimental groups: Group 1 (n=11), control, vaccinated only with QuilA adjuvant; Group 2 (n=11), vaccinated with 5 µg of antigens; Group 3 (n=11), vaccinated with 50 µg of antigens. After separated into three groups, the ewes will grazed and rotated into nine contiguous paddocks, three paddocks per group, with 0.3 hectares each, where they will remain for a period of 10 days in each paddock. The ewes of group 1 will occupy the paddocks of numbers 1, 4 and 7, group 2 the paddocks of numbers 2, 5 and 8 and group 3 the paddocks of numbers 3, 6 and 9. Four doses of vaccine will be given to the ewes: three doses prior to lambing and one dose four weeks after lambing. The lambs born from ewes in all groups will also be in other three experimental groups: Group 1, control; Group 2, vaccinated with 5 µg of antigens; Group 3, vaccinated with 50 µg of antigens. Lambs will receive five doses of the vaccine, the first three doses with intervals of three weeks each and the last two doses with intervals of six weeks. The animals will be weighed weekly and herbage samples will be taken to determine the number of infective larvae of gastrointestinal nematodes per kg of dry matter.