A deworming field trial with ivermectin (MSD) in reindeer

The relative plasma availabilities of ivermectin in reindeer (Rangifer tarandus tarandus) following subcutaneous and two different oral formulation applications

Background

Overwintering (breeding) reindeer (Rangifer tarandus tarandus) are commonly treated with ivermectin against parasitic infestations once yearly in autumn-winter roundups. The only preparations registered to reindeer are those for subcutaneous injection. However, also oral extra-label ivermectin administration is used. Twenty-six, 8-month-old reindeer calves were randomly allocated into three groups. Group 1 (n = 9) received oral ivermectin mixture (Ivomec® vet mixt. 0.8 mg/ml, oral ovine liquid drench formulation), Group 2 (n = 9) oral ivermectin paste (Ivomec® vet 18.7 mg/g equine paste), and Group 3 (n = 8) subcutaneous injection of ivermectin (Ivomec® 10 mg/ml vet inj.), each group at a dose of 200 μg/kg body weight. Blood samples were collected at treatment and at days 1, 2, 3, 6, 9 and 16 post treatment. Plasma concentrations of ivermectin were determined by high-pressure liquid chromatography (HPLC) with fluorescence detection.

Results

The peak plasma concentration (C_max) was reached by 2 days after each treatment. The C_max and Area Under Curve (AUC) differed significantly between the groups: C_max was 30.2 ± 3.9, 14.9 ± 5.7 and 63.1 ± 13.1 ng/ml, and AUC_∞ was 2881 ± 462, 1299 ± 342 and 6718 ± 1620 ng*h/ml for groups 1, 2 and 3, respectively (mean ± standard deviation).

Conclusions

The differences in plasma concentrations of ivermectin are concomitant with earlier observed differences in antiparasitic efficacy, which discounts the use of the equine paste in reindeer in favour of the oral ovine liquid drench formulation, or preferably, the reindeer-registered subcutaneous injection formulation.

Ivermectin treatment did not increase slaughter weight of first-year reindeer calves

To investigate if antiparasitic treatment of reindeer calves during the summer could increase their carcass weight during the slaughter period in autumn and winter, 529 reindeer calves were allocated to three groups, weighed, and marked with individually numbered plastic ear tags in early July, 1995. One of the groups was left untreated, another was treated with ivermectin injection at 200 micrograms/kg, and the third with pour-on ivermectin at 500 micrograms/kg. Following slaughter, carcass weights were received from 231 animals, and there was no difference between the treatment groups.

Gastrointestinal nematodes depress food intake in naturally infected reindeer

Models have predicted that directly transmitted macroparasites may influence the abundance of forage plants in herbivore grazing systems by reducing the food intake of their host. Evidence of parasite-induced alterations in host food intake is, however, limited mainly to sheep, cattle and laboratory rodents. We estimated the effect of naturally acquired parasite infections on the appetite of reindeer. Food intake was significantly lower in infected reindeer compared to animals in which the parasites had been experimentally removed. Among the infected animals there was a significant negative relationship between intensity of the directly transmitted macroparasites (i.e. gastrointestinal nematodes) and mean food intake, indicating that the lower food intake was caused by these parasites. The time-specific onset of depression in food intake is also consistent with seasonality in the pathogenic effect from gastrointestinal nematodes. This shows that parasite-induced changes in herbivore food intake is not restricted to agricultural systems, and implies that parasites may have impact on the dynamics of a wide range of herbivore plant communities.

Oral and parenteral administration of ivermectin to reindeer

The anti-parasitic effect of the orally administered paste formulation of ivermectin (Ivomec) in reindeer was evaluated by means of a trial designed to compare the efficacies of orally and s.c. administered ivermectin at the same dosage (0.2 mg kg-1 body weight) in naturally infected adult reindeer (n = 92). Both formulations were 100% effective against larvae of the warble fly, Oedemagena tarandi, while oral treatment was less efficacious than s.c. injection against parasitic nematodes. Both formulations, but particularly the injectable ivermectin treatment, increased the weight gain of pregnant females compared to that of those not treated.