FOALS RAISED ON PASTURE WITH OR WITHOUT DAILY PYRANTEL TARTRATE FEED ADDITIVE - COMPARISON OF PARASITE BURDENS AND HOST RESPONSES FOLLOWINGEXPERIMENTAL CHALLENGE WITH LARGE AND SMALL STRONGYLE LARVAE

Three groups of foals were raised under different management programs in this study: Group 1 (n = 6) and Group 2 (n = 6) were raised with th eir dams on pasture; Group 3 foals (n = 5) were raised under parasite- free conditions. Mares and foals of Group I received daily pyrantel ta rtrate (PT) treatment with their pelleted feed ration, whereas mares a nd foals of Groups 2 and 3 received only the pelleted ration, Pasture- reared foals were weaned and moved to a heavily contaminated pasture f or 5 weeks. Group 1 foals continued to receive daily PT treatment wher eas Group 2 foals received only the pelleted feed ration. Following th is period, all foals were moved into box stalls. Half of each group wa s challenged with 10(3) Strongylus vulgaris infective third-stage larv ae (L-3),5 x 10(3) Strongylus edentatus L-3 and 10(5) mixed cyathostom e L-3; the remaining half served as unchallenged controls. Necropsy ex aminations were performed 6-week post-challenge for evaluation parasit e burdens and lesions. Daily PT treatment of Group 1 reduced the paten t cyathostome infections of both mares and foals and was effective in reducing pasture burdens of infective larvae. Daily treatment of Group 1 foals during weaning continued to suppress EPG levels; however, it did not prevent large strongyle infections during the weaning period. Group 1 foals were more sensitive to challenge than Group 2 foals, whi ch did not exhibit any post-challenge disturbances. Group 1 foals were equally susceptible to challenge as parasite-free foals. (C) 1997 Els evier Science B.V.