Studies on the occurrence of anthelmintic resistance in goat parasites in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies in Parasitology at Massey University, Palmerston North, New Zealand
Loading...
Date
2010
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
Two studies were conducted to investigate anthelmintic resistance in goat parasites in
New Zealand. In Study 1 parasites from goats on a farm with a long history of
problems with anthelmintic efficacy were used to infect sheep for a controlled slaughter
study. Nineteen lambs were acquired, effectively drenched and housed. Each was
infected with a mixture of larvae comprising Haemonchus contortus, Teladorsagia
circumcincta, Trichostrongylus colubriformis and Oesophagostomum venulosum.
After 28 days lambs were restrictively randomised into 3 groups based on faecal egg
counts. Group 1 was left untreated (n=6), Group 2 (n=6) was given a single dose of
abamectin (0.2mg/kg) + levamisole HCL (8mg/kg) + oxfendazole (4.5mg/kg) (“Matrix
Oral Drench for Sheep”®, Ancare, New Zealand) and Group 3 (n=7) was treated at
twice the dose rate of Group 2. Fourteen days after treatment all animals were killed
for total worm counts. The mean burdens of T. circumcincta in Group 1 was 337, in
Group 2 was 68 (efficacy 80%) and in Group 3 was 10 (efficacy 97%). The mean
burdens of T. colubriformis in Group 1 was 375, in Group 2 was 220 (efficacy 41%)
and in Group 3 was 81 (efficacy 78%). Although the worm burdens in these lambs
were low, all animals were infected with each of these two species except for T.
circumcincta in Group 3 where only 3 lambs were infected. Efficacy against other
species was 100%. These results clearly indicate that a single dose of a combination
drench was ineffective against two species and even when a double dose was used the
efficacy against T. colubriformis was only 78%. In Study 2 a survey of drench efficacy
was conducted on 17 goat farms using the DrenchRite® larval development assay.
Evidence of concurrent resistance to benzimidazoles, levamisole and ivermectin was
detected in T. colubriformis and T. circumcincta on 11/17 and 3/14 respectively. Only
5 of 14 farms had previously undertaken some form of testing for drench resistance
prior to this survey. Evidence from these two studies suggests that severe anthelmintic
resistance is common on goat farms in New Zealand
Description
Keywords
Goat parasites, Drench resistance, Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis, Oesophagostomum venulosum