Comparative response of tall fescue (Lolium arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) swards to variation in defoliation interval and height : a thesis presented in partial fulfilment of the requirements for the degree of Master of AgriScience at Massey University

This thesis studies aspects of the epidemiology of Nematodirus spathiger and \nNematodirus filicollis, both are common and potentially pathogenic parasites of lambs \nin New Zealand. Three studies were undertaken; the first a presence/absence survey to \ndetermine the distribution of the two species on farms, the second examined the \nprevalence of benzimidazole (BZ) resistance in the two species and the third experiment \ninvestigated the requirements for chilling for N. filicollis eggs to hatch. \nThe first two studies utilised faecal samples from routine faecal egg counts and/or \nroutine faecal egg count reduction testing on farms. To identify the Nematodirus species \ninvolved, eggs from these samples were chilled and then incubated to facilitate hatching \nof N. filicollis, before larvae were recovered. The identity of the larvae was determined \nusing PCR of the ITS-2 region of rDNA. The third experiment used a bulk collection of \nN. filicollis from naturally infected lambs. Extracted eggs were incubated at \ntemperatures between 2.7°C - 9.9°C, for up to 224 days. The proportion of eggs \nhatching was assessed against chill units. Chill units (degree-day) were calculated by \nsubtracting the culture temperature from a constant threshold of 11°C and multiplying \nby the number of days for which the sample was cultured. \nIn Study 1, N. spathiger was present on all farms tested, while N. filicollis was found on \n76% of farms. Both species were distributed throughout New Zealand, with no regional \ndifferences. In Study 2, the BZ-resistance study, efficacies below 95% were recorded \nfor N. spathiger and N. filicollis on 95% (20/21) and 40% (4/10) respectively of farms \ntested. In Study 3, the chilling experiment, the overall hatching of N. filicollis eggs was \nlow, but increased with chill accumulation to plateau at about 11%, with 800-1000 chill \nunits required for maximum hatching. \nIn conclusion the two species of Nematodirus were commonly found on most New \nZealand farms. The prevalence of BZ-resistance in N. filicollis was lower than that in N. \nspathiger. N. filicollis required a considerable period of chilling to enable hatching to \noccur and this will influence their epidemiology.