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    Some aspects of the host-parasite relationship between goats and gastrointestinal nematodes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University
    (Massey University, 1994) Pomroy, William Ernest; Pomroy, William Ernest
    Experiments were conducted investigating the acquisition, by goats, of resistance to Haemonchus contortus and Trichostrongylus colubriformis. Neither 5.5 or 14 months old Saanen goats given a trickle infection with H. contortus, which was terminated with anthelmintic after 10 and 14 weeks respectively, showed significant resistance to a challenge infection. Serum pepsinogen levels rose significantly as a result of infection. Serum gastrin levels also rose as a result of infection but, following challenge, were generally higher for naive goats than previously infected goats. There were no significant correlations between worm counts, gastrin and pepsinogen levels at the time of slaughter. By contrast, a high level of resistance to T. colubriformis developed in 9 months old Saanen goats given trickle and two challenge infections. Goats exposed only to the two challenge infections developed worm burdens intermediate between, and significantly different from both trickle-infected and previously uninfected goats given just the second challenge. Both priming infections were removed with anthelmintic. Globule leukocyte (GL) counts in the proximal small intestine of trickle-infected goats were significantly higher than in goats given a single challenge infection, whilst counts for the group given two challenge infections were intermediate and not significantly different from other treatments. Nematode fecundity (eggs per female) and male:female ratios were also significantly decreased in the previously infected goats. Ninety four percent of all T. colubriformis were found in the proximal 50% of the small intestine in both young goats and older goats. Male:female ratios increased and eggs/female nematode decreased with distance down the small intestine. Only about 50% of adult T. colubriformis were recovered from recently killed goats by opening and massaging the small intestine under running water. Antiparasite activity of intestinal mucus from groups of Angora-cross goats killed 9, 18 or 27 days after infection with T. colubriformis, increased significantly in infected versus uninfected goats with no difference between infected groups. However, the establishment rate (57-67%) suggests little immunity was being expressed. Following infection, proximal small intestinal GL counts fell with time but there was still a clear negative relationship between GL counts and worm burdens. Mucosal mast cell and eosinophil counts showed no significant trends relative to duration of infection or worm burden. Differential cell counts were made using a monoclonal antibody to sheep mast cells developed with diaminobenzidine, combined with haematoxylin and Biebrich's scarlet. This method was shown to be superior to others tried. In Angora-cross goats killed sequentially after removal of an infection with T. colubriformis, proximal small intestinal GL counts increased with time. However, antiparasite activity of intestinal mucus was consistently low. GL counts in all these Angora-cross goats were generally higher further down the intestine beyond the location of a large proportion of the T. colubriformis burden. In Angora goats fitted with ileal cannulae and infected with T. colubriformis, antiparasite activity of ileal contents increased significantly with time after infection in all goats. However, the establishment rate (10.6-61.8%) indicated only a moderate degree of resistance was being expressed although a large proportion of established worms were inhibited L3s.
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    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
    (Massey University, 2010) Kamaludeen, Juriah
    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