Browsing by Author "Dowling, Andrew"

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    The prevalence and production effects of liver fluke (Fasciola hepatica) in New Zealand cattle including evaluation of diagnostic tests : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2023) Dowling, Andrew
    The liver fluke Fasciola hepatica, infects cattle worldwide and is considered a parasite of regional importance in New Zealand although the impact on milk production in that country have not been studied. The test characteristics of two antibody detection ELISAs; IDEXX ELISA (IDEXX Fasciolosis Verification) and an In-House assay using unrefined excretory secretory antigens, plus a coproantigen ELISA (Bio K 201–Monoscreen AgELISA) and faecal egg counts (FEC) were assessed against the gold standard of total fluke counts in naturally infected cattle (cows=29, steers=10). Vat milk of dairy herds on the West Coast of the South Island was assessed for liver fluke infection using the IDEXX ELISA in the autumn, near the end of one lactation (n=430), and spring, near the beginning of the subsequent lactation(n=403). A total of 156 questionnaires determining awareness of liver fluke infection and drenching practices were completed. A cross sectional study of 11 herds (n=1314 cows) in autumn and a longitudinal study of 4 herds (n=485 cows) in spring and autumn used the IDEXX ELISA (measured as SP%) on serum to analyse associations between liver fluke infection and milk production parameters in individual cows. A subset of cows was also faecal sampled for coproantigen and FEC analysis. Notably, a negative linear effect of the loge(total fluke count+1) on liveweight (p=0.02) was found and the coproantigen values showed a significant (p=0.01) quadratic effect for loge(total fluke count+1). The survey showed that infection of herds at a level likely to cause production losses on the West Coast is common, with regional clustering. Milk Fat % decreased 0.0004% points for every 1SP% increase (p=0.004), being 0.05 %points lower for cows with SP%150 than cows with SP%30, and 0.22 %points (p=0.014) lower in cows where SP% increased from ≤30 to ≥150 during lactation compared that those remained ≤30 with an economic cost of $55.19 per infected cow. Of the tests compared, the IDEXX ELISA was superior to the In-House ELISA for sensitivity (Se) and specificity (Sp) but the coproantigen ELISA had the highest Se (96%) and Sp (96%). Overall, liver fluke infection was common in dairy cows but the infection intensity was low, nevertheless a small effect on MF% was determined.