PROPHYLAXIS OF TRICHOSTRONGYLIDOSIS AND DICTYOCAULOSIS IN CALVES GRAZED ON ALPINE PASTURES - STRATEGIC USE OF DORAMECTIN POUR-ON IN JUNE AND SEPTEMBER

The effect of doramectin pour-on (Dectomax(R) 0.5% pour-on, Pfizer) ag ainst gastrointestinal nematodes (GIN) and lungworms was investigated in calves grazed on alpine pastures in Switzerland. Doramectin pour-on (0.5 mg/kg body weight) was administered topically to calves (n = 57, Group D) before and after the alpine grazing season (mid-June to end of September) when the calves were kept on altitudes between 1800 and 2600 m together with 20 untreated calves (Group K). Calves of both gro ups were grazed together during the alpine season and were subsequentl y moved to prealpine and home pastures where they were kept until stab ling tend of November). Faecal examinations, performed 4 to 5 weeks af ter anthelmintic treatment of Group D calves showed a marked reduction of the trichostrongyle egg output,which was also low in the untreated calves. Low numbers of Dictyocaulus-larvae were excreted by the calve s at turnout to the alpine pastures. At the end of September the mean excretion of Dictyocaulus-larvae had increased markedly in both groups . After treatment of Group D calves the larval output remained negativ e until stabling. In contrast? the larval excretion of the untreated c alves (Group K) reached highest levels at the end of October and 4 cal ves exhibited clinical signs of dictyocaulosis. The results indicate t hat the strategic use of doramectin pour-on in June and in late Septem ber provided good protection against severe infections with D. vivipar us. The infection level with GIN confirmed that these parasites are of minor relevance under the extensive grazing conditions on high alpine pastures.