The anthelmintic efficacy of moxidectin injection and albendazole controlled release capsules in 18 month old ewes in the autumn mating period.

Abstract

Sixty 18 month old Romney ewes were drenched orally with ivermectin at twice the recommended dose rate (400ug/kgL W) when introduced to the trial area on February the 25th 1995. Six days later all animals were weighed and allocated on the basis of liveweight(LW) to 1 of 3 equal sized treatment groups (n=20), faecal egg counts (FEC) were all negative at this time. Treatments were commenced at day 0 receiving either, moxidectin injection, (MI group) (Vetdectin Injection, Cyanamid/Ancare Ltd, Auckland) at 200ug/kgLW, or an albendazole controlled release capsule (AB group) (Extender 100 CRC, Nufarm Ltd, Auckland) with the third group serving as controls (CO group). All ewes grazed the same pasture and the natural challenge was reinforced by oral administration of 15 000 L3 Ostertagia circumcincta and 9 000 L3 Trichostrongylus colubriformis twice weekly until day 77 of the trial. The trial was terminated on day 84 with FEC recorded weekly and LW every fortnight. Weekly blood samples were taken for serum concentration measurements of pepsinogen, fructosamine, albumin and total protein. Five ewes from each group were slaughtered on days 21,42,63 and 84 for total worm counts. Mean group LW at day 0 for all 3 groups was 48.5kg, the LW change over the 84 day trial was significant (p = 0.05) for both the MI and AB groups but not the CO group. The difference in LW between the AB group, 54.5kg (sem 1.31) and CO group, 50.0kg (sem 2.47) was significant (p = 0.05) at day 84. However the MI group L W of 52.3kg (sem 1.84) was not significantly different from either AB or CO group LW's at day 84.

Significant differences were obtained between the CO group and AB and MI group concentrations of albumin, pepsinogen and fructosamine. The FEC of CO group ewes increased significantly (p = 0.001 ) from day 28 compared to AB and MI treatments to peak at a geometric mean of 400 epg on day 63. Significant suppression of FEC occurred in the MI and AB ewes compared to CO ewes between days 28 and 63 (p = 0.005). Ewes in the AB group maintained a very low geometric mean FEC for the duration of the trial. The MI treatment significantly (p = .005) suppressed FEC for the first 49 days compared to the CO group. Mean geometric worm burden of sheep at day 21 in the MI group was 33 and was significantly lower (p = 0.016) than ewes in groups AB and CO (887 and 867 respectively). The CO group worm burden fluctuated around 10 000 at days 42, 63 and 84 whilst both AB and MI groups had significantly reduced worm burdens on day 42 (p = 0.002) and at day 84 (p = 0.05) never exceeding 1000. Similar worm burdens of ca 2000 for the AB or MI groups resulted in a non-significant difference from the CO group at day 63. The results demonstrate that 18 month old ewes are susceptible to parasitic challenge in the autumn mating period. Considerable protection from parasitic infection can be obtained by either using moxidectin injection or the albendazole controlled release capsule.