Browsing by Author "Pomroy W"

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    A Field Evaluation of the LuciTrap and the Western Australian Trap with Three Different Baits Types for Monitoring Lucilia cuprina and Lucilia sericata in New Zealand.
    (15/09/2021) Brett P; Lawrence K; Kenyon P; Gedye K; Pomroy W
    Flytraps can be used on farms to monitor the populations of primary strike flies (Lucilia cuprina and Lucilia sericata) and, hence, offer a view regarding the incidence of flystrike on sheep. This study aimed to contrast the specificity and effectiveness of the LuciTrap with its combination of three chemical lures (Lucilures) and the Western Australian Trap with three bait types (LuciLure, Sheep liver with 30% sodium sulphide and squid). A mean model and rate model were fitted to the data. The mean model showed no difference (p > 0.05) in the mean weekly catch for L. cuprina between the Western Australian Trap with LuciLures and the Western Australian Trap baited with sheep liver with 30% sodium sulphide (p < 0.05). Whereas, for L. sericata, no difference (p > 0.05) was found between the Western Australian Trap with LuciLures, the Western Australian Trap baited with sheep liver with 30% sodium sulphide and the LuciTrap. The rate model illustrated that the Western Australian Trap with sheep liver with 30% sodium sulphide and LuciTrap did not differ (p > 0.05) for L. cuprina and L. sericata. Combined, these results indicate that New Zealand farmers can use either the LuciTrap or the Western Australian Trap with sheep liver with 30% sodium sulphide to monitor these target species.
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    CHANGES IN THE LEVELS OF THEILERIA ORIENTALIS IKEDA TYPE INFECTION IN HAEMAPHYSALIS LONGICORNIS NYMPHS OVER A SIX-MONTH PERIOD.
    (1/09/2021) Zhao Y; Lawrence KE; Minor M; Gedye K; Wang B; Pomroy W; Potter M
    This study aimed to investigate whether the infection intensity of Theileria orientalis Ikeda type organisms within Haemaphysalis longicornis larvae and nymph stages fluctuated over 6 mo after feeding as larvae on infected calves in the field. Naïve larvae, hatched from eggs, were fed on infected calves for 5 days while contained within cotton socks glued over the calves' ears. Larvae were first sampled immediately post-feeding and then sampled every 3 wk for 23 wk in total, after molting to nymphs. All larvae and nymphs were tested for T. orientalis Ikeda organisms using quantitative PCR. The qPCR results showed that the infection intensity of Haemaphysalis longicornis larvae and nymphs was not constant over the sampling period, and after initially dropping after molting to nymphs, it then rose with fasting to a maximum at 17 and 23 wk post-feeding. The significant rise in T. orientalis Ikeda organisms observed at 23 wk postfeeding may explain why more severe clinical cases of bovine theileriosis in New Zealand are seen in the spring when nymphs are the predominant instar questing.
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    Genetic susceptibility to Theileria orientalis (Ikeda) in Angus- and Hereford-sired yearling cattle born to dairy cattle on an endemically infected farm in New Zealand
    (Taylor and Francis Group, 5/03/2023) Lawrence K; Fermin L; Gedye K; Hickson R; lawrence B; coleman L; Pomroy W; Natalia M; Lopez- Villalobos N
    Theileria orientalis (Ikeda) was first detected in New Zealand in 2012, becoming endemic in most of the North Island, and can cause incidences of anaemia and death. Research has been performed in New Zealand on the incidence and severity of infection. Through this research anecdotal evidence has been found to suggest a potential genetic susceptibility component in the response of the host to the parasite. To investigate the genetic susceptibility of cattle to T. orientalis (Ikeda), 99 calves born in 2016 as part of a separate experiment and grown in six grazing herds, were examined for their response to the parasite. In addition to measuring live weight, two blood collections were taken in the first four months of life which were used to measure packed cell volume by haematocrit and qPCR to assess parasite load. Heritability was calculated and was low for parasite load, but the result indicates that there is some potential to increase resistance through selective breeding. The mechanisms of the differences in parasite load were not elucidated in this research; however, significant variation was found among herds and sires, indicating that both genetic selection and environmental management could be utilised to reduce parasite load in growing calves.
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    Prevalence of liver fluke on the West Coast
    (New Zealand Veterinary Association, 2021) Dowling AF; Howe L; Lawrence K; Pomroy W; Scott I
    A study of all herds (n=430) supplying Westland Milk Co-op were tested with an IDEXX Bulk Milk Elisa (BME) (IDEXX Fasciolosis Verification, IDEXX Europe BV, Hoofdorp, The Netherlands) which characterises herds into intensities of infection (Nil, Low, Medium, Strong). These equate to liver fluke infection prevalence of 0%, <20%, 20 – 50%, >50% within the sampled herd. Overall, the distribution of herds as analysed in the autumn of 2017 was Nil=31%, Low=11%, Medium=14%, Strong=43%. It was notable that some regions had much higher levels of infection than others.
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    Prevalence of liver fluke on West Coast farms of the South Island of New Zealand sampled in the autumn and spring of consecutive lactations
    (2021-07-19) Dowling A; Pomroy W; Howe L; Scott I; Lawrence K
    The aim of this study was to determine the occurrence of Fasciola hepatica infection in dairy cows in this West Coast of the South Island using an ELISA of bulk milk samples (n=430) collected on one of two occasions during March (autumn) 2017 and again in October (spring). All samples were analysed using the IDEXX Fasciolosis Verification kit which estimates the infection level in the herd in 4 categories; >50% infestation (strong); 20-50% infestation (medium); <20% infestation (low); no infection. A subset (n=99) were tested twice with a one week interval to determine repeatability. A short survey was also posted to each supplier with 157 completed. Of the 430 farms tested 133 (31%) were negative, 49 (11%) had a low infestation, 62 (14%) had a medium infestation and 186 (43%) had a strong infestation. GIS mapping of the farm locations indicated geographic grouping of farms with more severe fluke infestations. The 99 samples tested twice substantially agreed (Kappa = 0.7). Farms tested in both autumn and spring (n= 369) moderately agreed (Kappa 0.43) with an overall decrease in the spring. From the survey 85% of farmers were aware of liver fluke on their farm during the last 5 years and 70% treated their cows with a flukicide during the dry period (winter) including 92% of the farms that tested negative. This study indicates fasciolosis is common in this region with a disturbing number with a high prevalence in their herds. It also showed a decrease from autumn to following spring levels.
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    Review of the New Zealand Theileria orientalis Ikeda Type Epidemic and Epidemiological Research since 2012.
    (19/10/2021) Lawrence K; Gedye K; McFadden A; Pulford D; Heath A; Pomroy W
    This article sets out to document and summarise the New Zealand epidemic and the epidemiological research conducted on the epizootic of bovine anaemia associated with Theileria orientalis Ikeda type infection, which began in New Zealand in August 2012. As New Zealand has no other pathogenic tick-borne cattle haemoparasites, the effects of the T. orientalis Ikeda type infection observed in affected herds and individual animals were not confounded by other concurrent haemoparasite infections, as was possibly the case in other countries. This has resulted in an unbiased perspective of a new disease. In addition, as both New Zealand's beef and dairy cattle systems are seasonally based, this has led to a different epidemiological presentation than that reported by almost all other affected countries. Having verified the establishment of a new disease and identified the associated pathogen, the remaining key requirements of an epidemiological investigation, for a disease affecting production animals, are to describe how the disease spreads, describe the likely impacts of that disease at the individual and herd level and explore methods of disease control or mitigation.
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    The milk production impacts of liver fluke (Fasciola hepatica) infection in dairy cows on the West Coast of the South Island, New Zealand
    (Elsevier B V, 2025-05) Dowling A; Lawrence KE; Howe L; Scott I; Pomroy W
    The impact of fasciolosis has been estimated on many occasions and can vary from mild to severe effects on animal productivity. The aim of the current study was to utilise observations on seroconversion of dairy cattle to Fasciola hepatica over the course of a lactation and compare their milk production with other cattle who remained serologically negative throughout the same lactation. Four spring-calving dairy herds on the West Coast of the South Island of New Zealand were selected based on prior knowledge of endemic liver fluke infection. Over the four herds, a total of 485 cows were blood sampled twice during one lactation, in early November (spring) and early March (autumn). The F. hepatica antibody titre of F. hepatica antibody was quantified using a commercial ELISA test (IDEXX Fasciolosis Verification, IDEXX Europe BV, Hoofdorp, The Netherlands). Milk production was estimated by a series of 3–4 herd tests over the lactation where each cow is individually measured during the morning and evening milking on the same day with samples analysed for milk yield, milk fat (MF), protein (MP), lactose (ML) and total milk solids (MS). Energy corrected milk (ECM) was then calculated using the formula: ECM (kg/d) = 12.55 × MF (kg/d) + 7.39 × MP (kg/d) + 0.2595 × milk yield (kg/d). At the spring sampling, 52 % of cows had antibodies detected which increased to 63 % in autumn. For the sampled cows, those that were in the negative IDEXX test category in autumn and spring were categorised as ‘uninfected’ while those which were negative in spring and seroconverted to the strong positive category in autumn were categorised as ‘infected’. Those in the intermediate categories were ignored. A total of 235 cows were categorised as ‘uninfected’ at the spring testing, being in the negative IDEXX diagnostic category. Of those 235, at the autumn testing, 152 remained in the negative diagnostic category and 50 were in the strong positive IDEXX diagnostic category and were categorised as ‘infected’. A model was fitted which described the lactation curve of each milk component (MF, ML, MP, ECM), a variable describing the infection status of the cow was then tested in the model. The only significant change detected was mean Milk Fat (MF) % being 0.24 MF% points (95 % CI 0.04–0.44 %) lower for ‘infected’ compared to ‘uninfected’ cows. Using a value of6.044/kg MF New Zealand dollars (NZD) this represents an economic loss of NZD 60.2 per ‘infected’ cow in a West Coast herd. Although small, such an effect will still have an appreciable impact on the economic return to a dairy farmer.
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    The seroprevalence and spatial distribution of liver fluke infection in a sample of West Coast and Canterbury dairy herds
    (Elsevier B.V., 2025-01-17) Dowling A; Lawrence KE; Howe L; Scott I; Pomroy W
    The West Coast region of the South Island of New Zealand is recognised as having a high prevalence of liver fluke infection, however, few studies have tested this assumption. This study aimed to estimate the seroprevalence and spatial distribution of liver fluke infection in most West Coast and some Canterbury dairy herds using bulk milk ELISA. Herds were bulk milk sampled on three occasions, twice, a week apart in March 2017 (n = 430 and n = 99) and once in October 2017 (n = 412). The concentration of liver fluke antibodies was estimated using the IDEXX Fasciolosis Verification ELISA (IDEXX Europe BV, Hoofdorp, The Netherlands) on these bulk milk samples. Herds were categorised according to the test instructions, with “medium” (≥20 % cows infected) or “strong” (≥50 % cows infected) results designated as production limiting. All herds were also sent a short questionnaire about awareness of liver fluke and treatment in their herds. The agreement between the IDEXX results for 99 herds sampled twice in March 2017, and between the IDEXX results for March and October for all herds was assessed with a Kappa test. There was a substantial agreement between the two March tests, kappa = 0.7 (95 % CI 0.58–0.82) and moderate agreement between the March and October samples kappa = 0.41 (95 % CI 0.34–0.48). The results of the questionnaire were linked to the IDEXX results, and the distribution of herds categorised by their IDEXX result plotted. At the March and October samplings 0/35 (0 %) and 0/27 (0 %) Canterbury herds, 248/395 (63 %) and 193/385 (50 %) of West Coast herds had a production limiting seroprevalence of liver fluke infection. Mapping showed that West Coast herds with a production limiting infection were clustered in coastal areas, whereas those without, were clustered in inland valleys. The odds of a coastal West Coast dairy herd having a production limiting seroprevalence of liver fluke were 10.7 (95 % CI, 6.6–17.3) times that of an inland herd in March and 8.6 (95 % CI, 5.4–13.8) times in October. There was no effect on IDEXX ELISA SP% (p = 0.92) of herds which were treated for liver fluke at dry off soon after the March test compared to their SP% in the following October test, soon after calving. The results show that liver fluke infection is a potentially serious problem for West Coast dairy herds especially for those on coastal river plains prone to flooding.