PROPHYLAXIS OF BOVINE TRICHOSTRONGYLIDOSIS AND DICTYOCAULOSIS IN THE ALPINE REGION - COMPARISON OF AN EARLY AND LATE ADMINISTRATION OF THE OXFENDAZOLE PULSE RELEASE BOLUS TO FIRST YEAR GRAZING CALVES

The effect of the oxfendazole pulse release bolus (OPRB) administered at turnout, in May, or in mid-July on the development of infections wi th gastrointestinal nematodes and lungworms in first year grazing calv es was investigated with three groups of nine animals, all grazing the same pastures in the Swiss midland region. In the calves of Group A ( OPRB on 21 May) less than 20 eggs per gram of faeces (e.p.g.) and less than three Dictyocaulus larvae per 10 g (l.p. 10 g) of faeces were sh ed for a period of 126 and 140 days respectively. Towards the end of t he grazing period calves of this group excreted significantly higher l evels of lungworm larvae (P < 0.05) compared with the other groups. Pr ior to OPRB administration on 14 July, the calves of Group B developed subclinical infections with trichostrongyles and lungworms which were similar to the untreated control Group C. By 4 weeks after bolus-admi nistration the excretion of trichostrongylid egg and lungworm larvae d eclined to levels below 20 e.p.g. and six l.p. 10 g respectively. Seru m pepsinogen values of the calves of Groups A and B were significantly lower (P < 0.05) compared with the control animals on days 84 and 98 after turnout and reflected mainly subclinical infections. With the ex ception of one Group A calf developing clinical parasitic gastroenteri tis (p.g.e.) at the end of the season, clinical disease was not observ ed in the treated calves, while seven out of nine control animals graz ing on the same pastures exhibited clinical p.g.e. with mean serum pep sinogen values exceeding 4400 mU tyrosine. Calves of Groups A and B ga ined significantly more weight(P < 0.01) compared with Group C (+ 36 k g and + 41 kg respectively); differences between Groups A and B were n ot significant. The results indicate that in mixed grazing systems of treated and untreated calves, which are often found in the alpine regi on, administration of the OPRB in May or Jury provided good results wi th respect to performance of the calves. However, late administration of the OPRB has the additional advantage of coverage of the period of higher infection risk with trichostrongyles and lungworms in the late season until stabling, and should therefore be recommended.