Studies on the epidemiology of Nematodirus spathiger and Nematodirus filicollis in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand

Abstract

This thesis studies aspects of the epidemiology of Nematodirus spathiger and Nematodirus filicollis, both are common and potentially pathogenic parasites of lambs in New Zealand. Three studies were undertaken; the first a presence/absence survey to determine the distribution of the two species on farms, the second examined the prevalence of benzimidazole (BZ) resistance in the two species and the third experiment investigated the requirements for chilling for N. filicollis eggs to hatch. The first two studies utilised faecal samples from routine faecal egg counts and/or routine faecal egg count reduction testing on farms. To identify the Nematodirus species involved, eggs from these samples were chilled and then incubated to facilitate hatching of N. filicollis, before larvae were recovered. The identity of the larvae was determined using PCR of the ITS-2 region of rDNA. The third experiment used a bulk collection of N. filicollis from naturally infected lambs. Extracted eggs were incubated at temperatures between 2.7°C - 9.9°C, for up to 224 days. The proportion of eggs hatching was assessed against chill units. Chill units (degree-day) were calculated by subtracting the culture temperature from a constant threshold of 11°C and multiplying by the number of days for which the sample was cultured. In Study 1, N. spathiger was present on all farms tested, while N. filicollis was found on 76% of farms. Both species were distributed throughout New Zealand, with no regional differences. In Study 2, the BZ-resistance study, efficacies below 95% were recorded for N. spathiger and N. filicollis on 95% (20/21) and 40% (4/10) respectively of farms tested. In Study 3, the chilling experiment, the overall hatching of N. filicollis eggs was low, but increased with chill accumulation to plateau at about 11%, with 800-1000 chill units required for maximum hatching. In conclusion the two species of Nematodirus were commonly found on most New Zealand farms. The prevalence of BZ-resistance in N. filicollis was lower than that in N. spathiger. N. filicollis required a considerable period of chilling to enable hatching to occur and this will influence their epidemiology.