The effect of different levels of parasite infection was studied in 5-month old calves. Eighty-four calves were dosed with 0, 1000, 2000, 4000, 7000 or 10000 parasite larvae (L3) per day for 6 weeks (90% Cooperia, 10% other species), or were drenched 3-weekly, whilst grazing in one mob. Worm burdens were then determined in 3 calves per treatment. The remaining calves then grazed together for 11 weeks to determine carryover effects, during which they were all drenched at weeks 5 and 9. At the end of L3 dosing, there were no liveweight differences, but by week 5 of the carryover period, calves receiving 10000 L3 per day were 12 kg lighter than drenched or 0 L3 calves (P<0.05). This difference was maintained for the rest of the experiment. Cooperiaburdens (76000/calf) in 10000 L3 calves were at least double those on all other treatments (P<0.001). There was no relationship between L3 dose and worm burden for the other parasite species, or L3 dose and faecal egg count. This experiment has shown that for calves dosed with less than 10000 L3 per day, drenching does not increase liveweight gain when the parasite larvae are 90% Cooperia.

VT, Burggraaf, and MR Puha

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 23-27, 2007
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