Repeat dosing of ruminants over limited periods with the anthelmintic thiophanate
Baines, D.M.; Dalton, S.E.
Veterinary Record 103(24): 527-530
1978
ISSN/ISBN: 0042-4900 PMID: 741617 Document Number: 132134
Studies on experimentally infected lambs and calves showed that repeated daily doses of 3.5 to 10 mg/kg body-weight of thiophanate for 7 to 28 days reduced the output of viable nematode eggs to low levels, with no marked resurgence after completion of treatment. In lambs there was evidence of sterilization of female (and to some extent, male) Haemonchus contortus but not of Nematodirus battus (although eggs in utero were rare). In calves Ostertagia circumcincta was more susceptible to the anthelmintic than Cooperia oncophora. A dosage of 2.5 mg/kg twice daily to sheep for 10 or 20 days produced similar effects on viable egg output. Post mortem worm counts suggested that both treatments were effective against H. contortus and Trichostrongylus colubriformis. Less consistency, but still a high level of effect was shown against N. spathiger. Ostertagia was not removed by the 10- or 20-day regimes. Female worms of all 4 species showed abnormalities of the reproductive tract and few eggs were present in utero. Single daily doses of 20 mg/kg for 5 days in lambs had a high vermicidal effect against all stages of H. contortus, O. circumcincta, T. colubriformis and N. spathiger. During the early stages of treatment the hatchability of eggs was extremely low. In a field trial thiophanate was incorporated into feedblocks at a level calculated to provide ewes with 5 mg/kg/day. Ewes were allowed access to the blocks from 4 weeks before the expected start of lambing until 7 weeks after lambing. No post parturient rise in faecal egg counts was seen in treated ewes; in untreated controls a peak occurred 4 weeks after lambing. 20 mg/kg/day for 5 days given in feed to housed cattle reduced faecal egg counts to low levels which persisted for 3 weeks after the end of treatment. C. oncophora was the predominant nematode, with low levels of O. ostertagi also present.