Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random sample of beef cattle herds in the North Island of New Zealand.

METHODS: A cross-sectional prevalence study was conducted using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, levamisole and albendazole on 60 calves on each of 62 farms in the North Island chosen at random from farms that conformed with the selection criteria. Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident.

RESULTS: Of the farms that completed the FECRT, 4/61 (7%) showed ≥95% reduction in FEC for all anthelmintics tested. Resistance to ivermectin was evident on 56/61 (92%) farms, to albendazole on 47/62 (76%) farms, and to both ivermectin and albendazole on 45/61 (74%) farms. Resistance to levamisole was evident on only 4/62 (6%) farms. The parasites most prevalent in resistant populations cultured were Cooperia spp. On 45/61 (74%) farms where Cooperia spp were present in suffi cient numbers, resistance to both ivermectin and albendazole was evident. No cases of levamisole-resistant Cooperia spp were detected. Resistance of Ostertagia spp to ivermectin was evident on 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, and to levamisole on 4/46 (9%) farms.

CONCLUSION: Anthelmintic resistance in parasitic nematodes of cattle is common in the North Island of New Zealand. Beef farmers need to be aware of the risks posed by anthelmintic resistance, and routine FECR testing is recommended to ensure optimal productivity and to guide decision-making when purchasing anthelmintics to be used on-farm.     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand.

METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocy- clic lactone (ML) anthelmintics (n=32). Resistance to an an- thelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident.

RESULTS: Of the farms randomly selected, 36% showed ≥95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to iver- mectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated.

CONCLUSION: Anthelmintic resistance in parasitic nema-todes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers' opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef-cattle rearing farms in the North Island of New Zealand. METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age. RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8-12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levamisole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased. CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers' opinions were divided on many issues and the overall impression was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.     

Farm management practices associated with macrocyclic lactone resistance on sheep farms in New Zealand

AIM: To identify farm practices associated with the presence of resistance to a macrocyclic lactone (ML) anthelmintic on sheep farms in New Zealand.

METHODS: A cross-sectional study was conducted to test for associations between the presence of resistance to an ML anthelmintic (ivermectin) and management practices on sheep farms in New Zealand. Selection of farms was both random (n=80) and purposive (n=32; being farms with a history of suspected ML resistance). Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <95% reduction in FEC 7–10 days after treatment with a half dose of ivermectin (0.1 mg/kg). A logistic regression model was built to identify farm-level factors that were associated with the presence or absence of ML resistance.

RESULTS: Of the 112 flock managers that were approached for interview, 103 (92%) returned useable questionnaires. The odds of ML resistance were increased: on farms that had used long-acting ML products in ewes as a pre-lambing treatment for ≥3 of the previous 5 years (odds ratio (OR) = 7.2; 95% confidence interval (CI) = 1.7–30.3); on farms where <70% of the total stock units mid-winter were from sheep (OR=6.5; 95% CI=1.6–25.6); on farms which over the year purchased ≥10% of the number of sheep present mid-winter (OR=7.1; 95% CI=1.5–34.7); and on farms where the average wool diameter of the main flock was <37 (OR=4.1; 95% CI=1.1–14.7) microns. The model provided a good fit to the data (pseudo R²=0.64; Hosmer-Lemeshow statistic = 0.38).

CONCLUSIONS: Explanatory factors identified as associated with the presence of ML (ivermectin) resistance on farms included the use of long-acting anthelmintic formulations in ewes pre-lambing, sources of refugia of unselected parasites on the farm, breed of sheep and their requirements for anthelmintic treatments, and the importing of resistant parasites with purchased stock. The study provides support for controls that aim to provide refugia of susceptible worms and that minimise the risk of introduction of resistance through effective quarantine-drenching.     

Anthelmintic resistance in cattle nematodes on 13 south-west Victorian properties

Objective To report the level of anthelmintic resistance on 13 commercial cattle properties in south-west Victoria, Australia. Procedure Between 2006 and 2009 worm egg count reduction tests were conducted on calves on the 13 properties. Samples were collected 10–14 days post anthelmintic treatment and worm egg counts and larval differentiation tests were conducted. Resistance was defined if there was less than 95% reduction (lower confidence limit <90%) in the faecal worm egg count for the particular genus. Results The percentage of properties with anthelmintic resistance in at least one species was 54% for benzimidazole (BZ), 100% for levamisole (LEV) and for ivermectin (IVM) it was 100% for the half-dose (0.1 mg/kg) and 62% for the full dose (0.2 mg/kg). A substantial frequency of resistance was detected in Ostertagia ostertagi to BZ (5/11), LEV (3/3) and IVM (5/11), in Trichostrongylus spp. to BZ (4/7) and in Cooperia spp. to IVM (6/11). No resistance to LEV was detected in Trichostrongylus or Cooperia spp. Suspected IVM-resistant Trichostrongylus spp. and BZ-resistant Cooperia spp. were only detected on one property each. Conclusion This is the first Australian report of macrocyclic lactone-resistant O. ostertagi in the refereed literature. The frequency of resistance in O. ostertagi to BZ, LEV and IVM and in Trichostrongylus spp. to BZ in the present study appears higher than levels detected in the 2004–05 New Zealand survey, whereas the resistance frequency in Cooperia spp. to IVM and BZ was less.     

Field studies investigating anthelmintic resistance in young cattle on five farms in New Zealand

AIM: To investigate the efficacy of pour-on anthelmintics against field strains of parasitic nematodes in young cattle on five farms in New Zealand.

METHODS: Faecal nematode egg count (FEC) reduction (FECR) tests were carried out on five calf-rearing farms using pour-on formulations of levamisole, ivermectin, eprinomectin, and the simultaneous administration of levamisole and ivermec- tin. Faecal samples were collected per rectum before treatment and about 7, 14, 21 and 28 days after treatment, for FEC and faecal nematode larval culture.

RESULTS: Resistance (i.e. <95% reduction in FEC) of Cooperia oncophora to ivermectin and eprinomectin was identified on all five farms. There was limited evidence of possible emerging resistance in Ostertagia spp to ivermectin but not eprinomectin, in short-tailed larvae of Cooperia spp to ivermectin and eprinomec- tin, and in Trichostrongylus spp to ivermectin, eprinomectin and levamisole used separately. Levamisole was effective against C. oncophora, but had variable efficacy against Ostertagia spp in the calves in this study. Simultaneous treatment with levamisole and ivermectin pour-on formulations were effective against all genera on all farms.

CONCLUSIONS: To effectively manage roundworm parasites in their calves farmers need to be aware of the resistance status of the parasites on their farms. Levamisole is likely to be an effective anthelmintic on most farms at times of the year when the impact of Ostertagia spp is not high. Simultaneous administration of levamisole and ivermectin pour-on anthelmintics to cattle is likely to control both ML-resistant C. oncophora and stages of Ostertagia spp that are not controlled by levamisole alone.     

Anthelmintic resistance in New Zealand

Anthelmintic resistance was first confirmed in New Zealand in 1979 and since then has become common-place; more than 50 % of sheep farms now have detectable levels of resistance to one or more chemical classes of anthelmintic. Farmer drenching practices have changed little over the last 15–20 years and are clearly exerting a significant level of selection for resistance. In the absence of new chemical classes of anthelmintics, current parasite control practices will be unsustainable in the long-term. Once substantial resistance has developed, significant reversion to susceptibility is unlikely and re-introduction of failed drugs is likely to result in the rapid re-emergence of control problems. The number of anthelmintic treatments applied is not necessarily a reliable indicator of selection pressure and should not be the only factor considered in strategies for minimising the development of resistance. The relative potential of the different anthelmintics now available, particularly the long- acting products, to select for resistance varies with the way they are used and with other epidemiological and management factors; generalisations about their respective roles in the development of resistance are often unreliable. In many cases, literal extrapolation of recommendations for the management of resistance from Australia to New Zealand is unsupportable, given the differences in climate, parasite ecology and farming practices between the 2 countries. In the absence of a refuge for susceptible genotypes, as occurs when anthelmintic treatments are used as a means of generating low-contamination ‘safe’ pasture for young stock, the rapid development of resistance is likely. Anthelmintic treatments applied to animals with a high level of immunity, or which become immune while the anthelmintic is active, are likely to select for resistance faster than treatments applied to non-immune stock.     

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

AIM: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand.

METHODS: An interview-based cross-sectional study of grazing management and anthelmintic useage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand.

RESULTS: Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target sample size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased.

CONCLUSIONS: Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.     

Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random sample of beef cattle herds in the North Island of New Zealand. METHODS: A cross-sectional prevalence study was conducted using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, levamisole and albendazole on 60 calves on each of 62 farms in the North Island chosen at random from farms that conformed with the selection criteria. Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident. RESULTS: Of the farms that completed the FECRT, 4/61 (7%) showed > or =95% reduction in FEC for all anthelmintics tested. Resistance to ivermectin was evident on 56/61 (92%) farms, to albendazole on 47/62 (76%) farms, and to both ivermectin and albendazole on 45/61 (74%) farms. Resistance to levamisole was evident on only 4/62 (6%) farms. The parasites most prevalent in resistant populations cultured were Cooperia spp. On 45/61 (74%) farms where Cooperia spp were present in sufficient numbers, resistance to both ivermectin and albendazole was evident. No cases of levamisole-resistant Cooperia spp were detected. Resistance of Ostertagia spp to ivermectin was evident on 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, and to levamisole on 4/46 (9%) farms. CONCLUSION: Anthelmintic resistance in parasitic nematodes of cattle is common in the North Island of New Zealand. Beef farmers need to be aware of the risks posed by anthelmintic resistance, and routine FECR testing is recommended to ensure optimal productivity and to guide decision-making when purchasing anthelmintics to be used on-farm.     

Resistance to a triple combination of broad-spectrum anthelmintics in naturally-acquired Ostertagia circumcincta infections in sheep

Extract

To the veterinary practitioner, the challenge of managing a cat with renal failure is very real. The specific goals of therapy are to:     

Benzimidazole resistance in Nematodirus spathiger and N. filicollis in New Zealand

AIM: To determine the prevalence of benzimidazole resistance in Nematodirus spathiger and N. filicollis from a sample of New Zealand farms.

METHODS: The efficacy of albendazole (ABZ) against Nematodirus spp. was assessed by faecal nematode egg count reduction (FECR) tests undertaken in lambs aged 3–8 months old on 27 sheep farms throughout New Zealand. On each farm, groups of 10–16 lambs were either treated with ABZ (4.75?mg/kg) or remained as untreated controls. Faecal samples were collected from all animals at the time of treatment and 7–10 days later. Faecal nematode egg counts (FEC) were performed using a modified McMaster technique. Larvae were cultured from pooled faecal samples, collected 7–10 days after treatment from each group, by incubation at 20°C for 6 weeks, 4°C for 26 weeks then 13°C for 2 weeks. The resulting third stage larvae were identified to species using a multiplex PCR assay, that identified species-specific sequences in the second internal transcribed spacer region of ribosomal DNA. The efficacy of ABZ for N. spathiger and N. filicollis was calculated from the proportion of the two species in culture and the group mean FEC before and after treatment. Only farms with a mean of 10?epg for each species in untreated samples were included for analysis. Resistance was defined as an efficacy <95%.

RESULTS: On farms that met the threshold of 10?epg in faecal samples, benzimidazole resistance was found on 20/21 (95%) farms for N. spathiger compared with 4/10 (40%) farms for N. filicollis (p<0.05). In samples collected following treatment, a mean of 83 (min 46, max 100)% of Nematodirus spp. larvae recovered from the untreated groups were N. spathiger, compared with 94 (min 45, max 100)% in the ABZ treated groups (p=0.03). This change in percentage was not influenced by the overall efficacy of treatment based on the FECR test (p=0.324).

CONCLUSION: The results confirm the high level of resistance in N. spathiger in New Zealand and that benzimidazole resistance was more common in N. spathiger than N. filicollis. While resistance to benzimidazole anthelmintics has been reported previously in New Zealand, this is the first report of N. filicollis being resistant to benzimidazole anthelmintics.     

A Survey of Anthelmintic Resistance by Nematodes on Three Sheep and Two Goat Farms in Hisar (India)

Singh, S. and Yadav, C.L., 1997. A survey of anthelmintic resistance by nematodes on three sheep and two goat farms in Hisar (India). Veterinary Research Communications, 21 (6), 447-451     

Turbulence and change - the veterinary profession in a competitive environment

This paper examines the views of members of the veterinary profession towards the change in orientation of professional practice that is occurring. It contrasts the values of veterinarians with those of doctors, dentists, lawyers and accountants. Particular attention is given to the areas of business efficiency, competition and advertising.

Data was derived from self-completion questionnaires containing 40 Likert scales which were mailed to 300 members of each of the five professions.     

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

AIM: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand. METHODS: An interview-based cross-sectional study of grazing management and anthelmintic usage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand. RESULTS: Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target sample size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased. CONCLUSIONS: Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.     

An evaluation of techniques used for the detection of anthelmintic resistance in nematode parasites of domestic livestock

In vitro and in vivo techniques used for the detection of anthelmintic resistance are reviewed in terms of their versatility, reliability, accuracy, cost and simplicity. The faecal egg count reduction test is considered the most suitable for field screening of resistance but the larval development assay is likely to prove a valuable adjunct in such investigations. Other in vitro techniques, such as egg hatch tests, larval motility and tubulin binding assays are recommended as suitable only for research investigations. Similarly, in vivo procedures such as the critical and controlled anthelmintic efficacy tests are considered to be appropriate only for specific research purposes because of the costs involved in such studies.     

A cost-benefit analysis of pre- and post-lambing anthelmintic treatments to twin-bearing ewes on commercial farms in the southern North Island of New Zealand

Abstract

AIM: To conduct a cost-benefit analysis of the administration of anthelmintics to adult ewes around lambing.

METHODS: Production data from comparisons of different anthelmintic treatments with no treatment were used in a cost-benefit analysis. The data were from 14 trials (part of an experiment carried out on one farm in 1 year) conducted on sheep and beef farms (eight in 2011 and six in 2012) in the Wairarapa region of New Zealand. The cost structure involved the purchase price of products and the labour cost of administration. The four key benefits identified for the calculation of economic returns, relative to untreated ewes, were: increased value of ewes sold (culled) at weaning, additional lambs weaned related to ewe liveweight at mating, increased total weight of lamb weaned per ewe, and reduced number of ewes requiring removal of soiled wool at weaning due to a lower dag score. Commercial values for these variables as at December 2013 were used, with the measured production data, to calculate a net (NZ$) benefit for every treatment-trial combination.

RESULTS: The economic return on treating ewes around lambing with anthelmintics was highly variable and across all trials treatment resulted in a financial loss in 18/38 (47%) groups of ewes. The mean net benefit from pre-lambing administration of a controlled release capsule (CRC) containing albendazole and abamectin was 5.36 (95% CI=?2.64 to 13.35) $/ewe, but overall was not different from zero (p=0.171). A breakdown of the overall gross benefit into its various components showed that weight of lamb weaned per ewe had the largest influence (a mean benefit of $5.68/ewe), followed by ewe liveweight pre-mating ($2.45/ewe), ewe liveweight at weaning ($0.66/ewe) and reduced dag score ($0.15/ewe). Other anthelmintic treatments all showed highly variable responses amongst trials, with some negative cost-benefits. There was no significant difference between any of the treatments except a short-acting oral treatment at tail-docking had a lower net benefit than a CRC containing albendazole administered pre-lambing (p<0.05).

CONCLUSIONS: A positive financial return resulting from the anthelmintic treatment of adult ewes around lambing is neither consistent nor predictable, and is often not achieved. Given that the additional costs of accelerating the development of anthelmintic resistance were not included in these calculations, farmers need to consider carefully the merits of administering anthelmintics to ewes around lambing.     

A survey of the prevalence of emerging macrocyclic lactone resistance and of benzimidazole resistance in sheep nematodes in the lower North Island of New Zealand

AIM: To investigate the occurrence of emerging macrocyclic lactone (ML) resistance and of resistance to benzimidazole anthelmintics on a number of sheep farms in the North Island of New Zealand.

METHODS: On commercial sheep farms (n=30) in the Taihape district in the North Island of New Zealand, 30 animals were randomly allocated to one of two equal-sized groups and treated with either half of the recommended dose rate of ivermectin (half of 0.2 mg/kg), or with the full recommended dose rate of oxfendazole (4.5 mg/kg). The ivermectin treatment only was used on a further six properties. Faecal egg counts, accompanied by pooled larval cultures, were conducted on all samples at the time of treatment and 7–10 days later.

RESULTS: Resistance, as indicated by a <95% faecal egg count reduction (FECR) in both instances, was found to oxfendazole on 13/30 (43%) farms and to a half dose of ivermectin on 12/36 (33%) properties. For oxfendazole, such resistance was found to involve all six nematode genera whereas for ivermectin it was almost entirely restricted to Ostertagia and Cooperia infections.

CONCLUSIONS: These results indicate that emerging ML resistance may be more common on sheep farms in New Zealand than is generally realised. They also suggest that the half-dose ivermectin faecal egg count reduction test (FECRT) may offer some very practical benefits for parasite control by providing early warning of developing resistance to ML drenches and by signalling the possible imminent failure of these at their therapeutic dose rates. The sensitivity and reliability of this procedure may be further enhanced by the inclusion of larval cultures.     

Facial eczema management protocols used on dairy farms in the North Island of New Zealand and associated concentrations of zinc in serum

AIMS: To describe and evaluate the current practices used to manage and prevent facial eczema (FE) in North Island dairy herds, and determine the within-herd prevalence of cows with elevated activities of gamma glutamyl transferase (GGT), and with concentrations of Zn in serum <18?μmol/L.

METHODS: Between January and May 2014, 105 herd managers from throughout the North Island of New Zealand were invited to participate in the study when regional spore counts for Pithomyces chartarum started to rise towards 30,000 spores/g pasture. Managers selected 10 representative cattle that were weighed and blood-sampled by the herd veterinarian. Blood samples were analysed for concentrations of Zn in serum and GGT activity. Pasture samples were also collected and submitted for spore count estimation. Finally a survey of farm management practices relating to prevention of FE was completed by the herd manager. A mixed-effects logistic regression model was used to determine associations between herd-level and cow-level explanatory variables and the probability of a cow having a concentration of Zn in serum <18?µmol/L.

RESULTS: Of the 1,071 cows tested, 79 (7.3 (95% CI=5.8–9.0)%) had GGT activity in serum >300?IU/L, and 35/106 (33 (95% CI=24.2–42.8)%) herds had ≥1 of the 10 cows sampled with GGT activity >300?IU/L. Of the 911 cows that were being treated with Zn, concentrations of Zn were between 18–35?μmol/L in 398 (43.6 (95% CI=40.4–46.9)%) cows, were >35?μmol/L in 32 (3.5 (95% CI=2.4–4.1)%) cows, and <18?μmol/L in 479 (52.6 (95% CI=49.3–55.9)%) cows. After adjusting for the confounding effect of region, the odds of a cow having concentrations of Zn in serum <18?μmol/L were 5.5 (95% CI=1.1–29) times greater for cows supplemented with zinc in water compared with those supplemented by drenching. Of the 105 herd managers, 103 (98%) stated that they had access to regional spore count data, but only 35/105 (33%) reported that they measured spore counts on their own farm. Overall, 98/105 (93%) managers reported that they had some form of FE management programme in place. Fungicides were used on their own or in combination with zinc treatments in 10 herds, ZnSO₄ in water troughs was used in 68 herds, oral drenching with ZnO in nine herds, and ZnO supplied in-feed in 26 herds. Estimated daily dose rates of zinc were less than that required to treat a 400?kg cow on 42/68 farms that administered ZnSO₄ in the water or ZnO as a drench.

CONCLUSION AND CLINICAL RELEVANCE: This study has shown that FE management on dairy farms in the North Island of New Zealand could be substantially improved. It is likely that improved FE management would occur if herd managers were provided with more feedback on the success (or otherwise) of their FE management programmes.     

Evidence that moxidectin is a greater risk factor than ivermectin in the development of resistance to macrocyclic lactones by Ostertagia spp in sheep in south eastern Australia

AIM: To determine associations between resistance of Ostertagia (= Teladorsagia) spp to macrocyclic lactone (ML) anthelmintics and history of use of anthelmintics, by type, on commercial sheep farms in temperate regions of southern South Australia and Victoria, Australia.

METHODS: Faecal egg count reduction tests (FECRTs) were conducted during a 2.5-year period (from August 2001 to January 2004) and records of the type of anthelmintic used in the 5 years preceding the FECRTs were collected from commercial sheep farms (n=103) in southern South Australia and Victoria, and data analysed retrospectively. ML resistance was defined as <95% reduction of Ostertagia spp 10–14 days after treatment with ivermectin (IVM), orally, at half the manufacturer's recommended dose rate. Use of anthelmintics in the preceding 5 and 10 years on each property was classified according to the nett number of years each of the following classes of drug had been used: IVM oral liquid (IVO), IVM controlled-release capsules (CRCs), abamectin (ABA), moxidectin (MOX) or a non-ML an- thelmintic. The prevalence of ML resistance, by property, was analysed for associations with prior use of anthelmintics.

RESULTS: Resistance by Ostertagia spp to ML anthelmintics was evident on 51/103 (49.5%) properties. The prevalence of resistance was lowest (23%) on properties on which MOX had not been used, and was significantly higher (64–77%) on properties on which MOX had been used for ≥2 of the preceding 5 years (p<0.001). In contrast, the prevalence of resistance was highest (70–74%) on the properties on which IVM, or IVM and/ or ABA, had not been used in the previous 5 years (on which the use of MOX was predominant), and was markedly lower (20– 42%) on properties that had used IVM or IVM and/or ABA for at least one of the preceding 5 years. Prevalence of resistance was higher for properties on which the only ML anthelmintic used was MOX (19/29=66%) than for those on which the only ML used was IVO (2/19=11%; p<0.001). Properties on which the only ML used was MOX were 2.72 times more likely to have resistance than properties on which the only ML used was IVO (95% confidence interval (CI) = 1.01–5.08).

CONCLUSION: Use of MOX for ≥2 of the preceding 5 years was associated with a higher prevalence of resistance to ML by Ostertagia spp on sheep farms in south eastern Australia than the use of IVO.