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The effect on liveweight gain of using anthelmintics with incomplete efficacy against resistant Cooperia oncophora in cattle
Veterinary Parasitology 251 (2018) 56–62
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Research paper
The effect on liveweight gain of using anthelmintics with incomplete efficacy against resistant Cooperia oncophora in cattle Paul M. Candy, Tania S. Waghorn, Chris M. Miller, Siva Ganesh, Dave M. Leathwick
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AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, 4442, New Zealand
A R T I C L E I N F O
A B S T R A C T
Keywords: Cattle Cooperia Anthelmintic resistance Productivity loss
A replicated field trial was conducted to measure the effect on liveweight gain of failing to adequately control anthelmintic resistant populations of Cooperia oncophora and to determine whether populations, and hence production losses, increased with time. Eight mobs of 10 Friesian-Hereford calves were run on independent farmlets from January to December, over each of two years. All mobs were routinely treated with a pour-on formulation of eprinomectin every six weeks, which controlled parasites other than Cooperia. Four mobs also received six weekly treatments with an oral levamisole plus albendazole combination anthelmintic to control Cooperia. Liveweights, condition scores, faecal egg counts and larval numbers on pasture were measured throughout. In the first year animals treated with eprinomectin alone were 12.9 kg lighter in November than those treated with eprinomectin plus albendazole and levamisole, however, in the second year there was no difference between the treatment groups. The data, therefore, support the view that while C. oncophora is less pathogenic than other cattle parasite species it can still cause production losses when present in sufficient numbers. In the first year of the study, parasite load, as measured by faecal nematode egg count and larval numbers on herbage, tended to be higher and calf growth rates lower than in the second year. In both years, counts of infective larvae on herbage declined over winter–spring to be at low levels before mid-summer. This suggests that the carry-over of infection from one crop of calves to the next was relatively small and hence that the level of challenge to the young calves at the start of each year was largely due to the effectiveness of the quarantine treatments administered when the animals arrived on the trial site. Low survival of larvae on pasture between grazing seasons, resulting in small larval populations on pasture when drenching programmes start each summer, might help to explain the widespread development of anthelmintic resistance in this parasite under New Zealand grazing systems.
1. Introduction Internal parasites are regarded as an important production limiting factor by a majority of New Zealand cattle farmers (Jackson et al., 2006). The recent emergence of anthelmintic resistance in pathogenic species such as Ostertagia ostertagi (Waghorn et al., 2016) is certain to enhance this view, and is a potentially serious future problem for the cattle industry. The cost of covert (undetected) resistance in parasites of sheep has been estimated at up to 14% of lamb carcass value (Sutherland et al., 2010; Miller et al., 2012), but equivalent estimates for cattle have not previously been determined. In New Zealand, Cooperia spp. dominate infections in cattle under 12–18 months of age. Cooperia oncophora resistant to the macrocyclic lactone (ML) class of anthelmintics are present on almost every farm in the country (Mason and McKay, 2006; Waghorn et al., 2006; Leathwick
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and Miller, 2013) and many of these populations are also resistant to benzimidazole anthelmintics (Waghorn et al., 2006). Despite this many New Zealand farmers continue to use single action ML products (Jackson et al., 2006) and most use pour-on formulations which are unlikely to deliver high efficacy against C. oncophora (Leathwick and Miller, 2013). The continued use of these products is likely to reflect the perception, held by most New Zealand cattle farmers, that anthelmintic resistance is not a significant animal health issue (Jackson et al., 2006). Consequently, many farmers are likely to be failing to control C. oncophora on their farms, and presumably they continue to do this because they see no indication of parasitism in the treated animals. While it is generally considered that Cooperia spp. are of secondary importance as parasites of cattle (Brunsdon, 1964; Familton, 2001; Sutherland and Scott, 2010) there is evidence that infection can result in detrimental effects on animal growth (Coop et al., 1979; Stromberg
Corresponding author. E-mail address: [email protected] (D.M. Leathwick).
https://doi.org/10.1016/j.vetpar.2017.12.023 Received 2 October 2017; Received in revised form 29 December 2017; Accepted 29 December 2017 0304-4017/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Mean ( ± 95% CI) liveweights for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines).
consisted of 5 paddocks, one from each cluster, which ensured that none of the paddocks within a farmlet were adjacent to each other and minimised the chances that any underlying pattern in the soil or pasture could influence the response to treatment. Each farmlet was randomly allocated to one of two treatments. Hence, eight farmlets, each of approximately 3 ha, were established in two complete replicate blocks of four, with the four farmlets within each block allocated to two replicates of two treatments. Prior to the commencement of this trial the site was grazed with untreated 18–24 month-old cattle for several months in order to contaminate the site with cattle parasites, as previously it had been grazed exclusively with sheep for many years.
et al., 2012; Leigh and Hunnam, 2013). Part of the explanation for this apparent contradiction may lie in the levels of challenge to which cattle are exposed. Logically, continued use of a less than fully effective anthelmintic will result in increased levels of pasture contamination and subsequently the number of larvae ingested by grazing livestock. Thus, long-term use of single-active ML products might be expected to result in an accumulation of infective Cooperia spp. larvae on pasture and an increased impact on animal performance. Hence, a parasite with low inherent pathogenicity may have a greater impact as the numbers to which a host is exposed increase. The current study was, therefore, instigated to quantify the effect on liveweight gain of failing to adequately control C. oncophora by using single action ML pour-ons against a resistant worm population, and to determine whether this increased over time through any accumulation of larvae on pasture.
2.1. Animals In January 2010, 80 newly weaned Friesian-Hereford cross calves were purchased at a commercial stock sale and transported to the farm. These animals were selected based on their uniformity of breed, size and condition, with no consideration given to their farm of origin or the anthelmintic resistance status of any parasites they may be infected with i.e. it was assumed that they would have a parasite infection and that any C. oncophora they were infected with would be largely resistant to ML anthelmintics. On their arrival at the research farm all calves were administered an oral dose of 0.2 mg/kg ivermectin (Ivomec, Merial Ancare New Zealand Limited, Auckland, New Zealand) which removed all parasite species except C. oncophora (mean post-treatment FEC was 128 eggs per g faeces (epg) and cultures were 96% Cooperia
2. Methods A replicated field study was conducted on the Flock House Research farm near Bulls in the Manawatu region of the North Island of New Zealand, from January 2010 to December 2011. An area of approximately 24 ha was initially divided into 2 replicate blocks before each of these was divided into 20 adjacent paddocks which were grouped into 5 ‘clusters’ of 4. The four paddocks within each cluster were then randomly allocated to one of four ‘farmlets’, a farmlet being a self-contained suite of paddocks carrying one group of animals and a single discrete worm population. Each farmlet, therefore, 57
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Fig. 2. Geometric mean ( ± 95% CI) faecal nematode egg counts (eggs per gram) for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines). Treatment dates were 2 Feb., 18 Mar., 27 Apr., 8 Jun., and 19 Jul in 2010 and 1 Feb., 16 Mar., 28 Apr., 14 Jun., and 26 Jul. in 2011.
Zealand) at the manufacturer’s recommended dose rate of 0.5 mg/kg liveweight, administered along the backline of each animal from shoulder to rump. In addition, Treatment 2 calves were also administered an oral dose of a combination anthelmintic delivering 7.5 mg levamisole and 10 mg albendazole per kg liveweight (Arrest C; Merial Ancare New Zealand Limited, Auckland, New Zealand). All anthelmintic doses were calculated based on the heaviest calf in each group at the time of treatment.
spp. and 4% Ostertagia spp.) The animals were then rotationally grazed over all trial paddocks on daily shifts in order to further contaminate the site prior to the trial commencing in February. At the commencement of the trial the calves were randomly allocated on the basis of liveweight into eight groups of 10 and each of these groups was randomly assigned to a farmlet where they were rotationally grazed around their respective suite of paddocks on approximately twice weekly shifts. In year 2, a similar process of purchasing animals was followed except that in order to prevent the introduction of additional parasites, all introduced calves were treated orally with a combination anthelmintic delivering 8.0 mg/kg levamisole, 4.5 mg/kg oxfendazole and 0.2 mg/kg abamectin (Matrix C; Merial Ancare New Zealand Limited, Auckland, New Zealand). Ten random FECs collected 10 days after this treatment were all zero.
2.3. Faecal nematode egg counts (FEC) Infection levels in the calves were monitored using FEC, at approximately three to six weekly intervals, including on the day they received each of their anthelmintic treatments. Faeces collected per rectum was placed in individually labelled plastic screw-top containers and returned to the laboratory for processing. The number of strongylid eggs present in a 4 g subsample was determined using a modified McMaster method in which each egg counted represented 25 epg (Lyndal-Murphy, 1993). Any faecal material remaining after each collection was pooled by group and cultured at 22 °C for 14 days to produce infective third stage larvae (L3) for identification. These were extracted from the culture material by baermannisation, concentrated by sedimentation in water at 10 °C, and identified to genus. Ten to 14 days after the second (March) and fifth (July) anthelmintic treatments in Year 1, and the first (February) and fifth (July) treatments in Year 2, calves were resampled for FEC, in order to
2.2. Treatment structure The treatment structure consisted of two treatments with four replicates of each. All calves received a programme of five anthelmintic treatments at 42-day intervals (the eprinomectin product label claims persistent activity against Cooperia and Ostertagia spp. of 21 and 28 days, respectively, and states that treatment intervals of up to 56 days should be effective at controlling these species), commencing in February each year. All calves were treated with eprinomectin (Ivomec Eprinex Pour on; Merial Ancare New Zealand Limited, Auckland, New 58
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Fig. 3. The percentage ( ± 95% CI) of infective third stage larvae (L3) recovered from faecal cultures in A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines), and square symbols represent Cooperia spp. and circles represent Ostertagia spp. Diamonds indicate samples collected 10–14 days after treatment.
with one experimental factor (2 Treatments) and one repeated factor (5 Weeks). Animals were therefore treated as genuine replications. Linear mixed effects models were utilized with ‘Animal’ as a random effect to capture appropriate structure for ANOVA. Replicate (the two replicate blocks) was included as a fixed effect. When the interaction and/or main effects in the ANOVA was significant (p-value < 0.05), the nature of these effects was investigated using pairwise comparisons of the treatment means. For the 2010 liveweights, data were transformed by square root in order to satisfy the assumptions for the ANOVA, however, in 2011 no transformation was required. In both years the liveweight of the calves at the beginning of the trial (February) was included in the model as a covariate. For analysis of FEC the counts taken soon after treatment to measure efficacy were removed from the analysis because these contained large numbers of zeros. The remaining data were transformed by Log10 + 1 prior to analysis. For comparison of pasture larval infestations (i.e. L3/kg DM) repeated measures ANOVA was used with two treatments and 11 repeated measurements. Because only some paddocks were sampled and the experimental unit was the worm population, farmlets were used as genuine replicates and the data from the paddocks within the farmlets were averaged. In both years the counts of L3/kg DM were transformed by Log10 +1 to meet the assumptions for ANOVA.
measure the efficacy of the treatment. Efficacy was estimated by comparing the pre- and post-treatment mean FEC for each group of calves, and calculating the percentage reduction in undifferentiated FEC. Also, efficacy against the main parasite genera was calculated after partitioning the total FEC based on the proportion of each genus recovered from the corresponding faecal culture. 2.4. Parasite larvae on pasture Pasture samples (‘plucks’) were taken from one paddock within each farmlet at irregular intervals from January to December, with additional paddocks in each farmlet being sampled in late autumn (May) and late spring (November) each year. Samples were collected by plucking pasture between the thumb and index finger while walking transects across a paddock. A minimum of 300 g of pasture, made up of 200–300 plucks from a single paddock, constituted one sample. Samples were soaked in water plus detergent overnight and the L3 were concentrated by sedimentation. After settling overnight at 4 °C, the water containing L3 was siphoned down to 10 ml and the larvae identified to genus and counted. 2.5. Statistics For measurements where the experimental unit was an individual animal (i.e. liveweight and FEC) a repeated measures ANOVA was used, 59
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Fig. 4. Pasture pluck results (mean L3/kg DM ± 95% CI) for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pouron plus an albendazole + levamisole combination oral drench (dashed lines).
3. Results
difference of 15 kg on 1 September (p < 0.005) (Fig. 1a). However, after that the liveweights converged somewhat with a final liveweight difference of 12.9 kg (p < 0.06). Six of the last eight liveweight comparisons were significantly different (p < 0.05) or approached significance (p < 0.072). In 2011, the liveweights remained similar throughout the trial with no significant difference between the treatment groups (Fig. 1b). Noticeably, the weight gains in the two years were quite different with the final (December) liveweights being 346 kg and 429 kg in 2010 and 2011, respectively.
3.1. Treatment efficacy As expected the efficacy of the two treatments was different. Treatment 2 (eprinomectin + levamisole + albendazole) consistently achieved high efficacy, averaging 98.5% (range 97%–100%) faecal egg count reduction over the duration of the trial. In contrast, Treatment 1, the eprinomectin alone averaged only 51% (range 27%-79%) reduction in FEC. Larval identification from faecal cultures collected after treatment indicated that Cooperia was the dominant (> 95%) genus surviving treatment. Calculating efficacy after partitioning of FECs to genera based on the proportions recovered from the faecal cultures showed that efficacy of all treatments against Ostertagia spp. and Trichostrongylus spp. exceeded 98%. Similarly, efficacy of treatment 2 (the combination of three actives) against Cooperia spp. exceeded 97% in all cases. Efficacy of the eprinomectin alone against Cooperia spp. ranged from 18% to 73%.
3.3. FEC Despite the differences in efficacy of the anthelmintic treatments, the faecal egg counts outside of the post-treatment intervals (i.e. the 3–4 weeks after treatment) were not that different (Fig. 2). In 2010, the treatment effect had a p-value of 0.098 but the interaction with time was highly significant (p < 0.0001), indicating that there was a different pattern of FEC between the treatments over time (Fig. 2a). The paired comparisons indicated that on some occasions both treatment groups had similar FECs, on two occasions (July and November) Treatment 2 FECs were lower and on one occasion (June) Treatment 2 FECs were higher than Treatment 1 FECs. In 2011, the FECs overall tended to be lower than in 2010, and there were no differences between the Treatment groups (Fig. 2).
3.2. Liveweight At the commencement of the trial in each year, calf liveweights were similar by virtue of the randomisation to group i.e. liveweights were used to allocate animals to farmlet and treatment so they would be expected to be similar. In 2010 average liveweight between the two treatments progressively diverged with time, reaching a maximum 60
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et al., 1988; Armour 1989). In addition, when the trial calves were brought onto the site they were initially treated only with ivermectin, which did not entirely remove the C. oncophora infections. The mean FEC of these calves, after the ivermectin treatment, was 128 epg (96% Cooperia spp.). With only a short period of grazing by these calves before the trial started, it might reasonably be expected that the numbers of Cooperia spp. L3 on pasture would have been relatively low, and that numbers would have built up with time, especially in the eprinomectin only groups which failed to reduce faecal egg output to low levels. In both years, FECs initially rose in both treatment groups over the summer-autumn period, indicating that the calves were picking up ongoing infection. However, FECs then declined through the winter to be low in both treatment groups by spring (September). Similarly, L3 numbers on pasture also increased initially but then declined relatively quickly to be at low levels at the end of spring-early summer (Fig. 4). Thus, there appeared to be little carry-over of pasture larval infestations from autumn-winter to the following spring-summer with, in both years, L3 numbers declining to low levels before the introduction of new season calves in January-February. It seems likely therefore that the higher levels of pasture contamination in the first year compared to the second year was a direct result of the effectiveness of the quarantine treatments given to the trial calves on their arrival. In the first year, an ineffective treatment was given deliberately in order to ensure contamination of the pastures with resistant Cooperia. This was confirmed by positive egg counts in the calves after treatment. In contrast, in the second year, this quarantine treatment was a combined treatment with abamectin, levamisole and oxfendazole, given to prevent the introduction of any additional parasites, and the effectiveness of this treatment was confirmed by the absence of eggs in the FEC. Given the apparent low level of persistence of the L3 population on pasture between grazing seasons, this suggests that the challenge facing the young calves each summer was largely determined by the efficacy of the quarantine treatment. Further work, supporting this interpretation of the data can be found in Sauermann and Leathwick (2018). There is little doubt that gastro-intestinal nematodes are capable of causing significant production losses in cattle (Hawkins 1993; Charlier et al., 2014), however, the specific role of Cooperia species is less clear. Artificial challenge experiments (Coop et al., 1979; Louvandini et al., 2009) along with productivity studies in feedlots (Stromberg et al., 2012; Fazzio et al., 2014) and with animals grazing pasture (Leigh and Hunnam 2013) indicate that Cooperia infection can result in reduced feed intake, impaired metabolism and reduced growth rates. The magnitude of the reduced growth rates attributable as a result of infection with Cooperia, irrespective of the species involved, are not high in any of these studies, ranging from 87 to 121 g/day. In the current study differences in growth were lower than these values, averaging only 47 g/day in 2010 and close to zero in 2011. However, the periods over which measurements were made differed considerably between studies, from 250 to 300 days in the current study to only 40–65 days in the earlier ones. The longer time period encompassed a period after which the animals would have been expected to have developed significant immunity to Cooperia infection (Armour, 1989) and this was reflected in a lesser effect of infection i.e. in 2010 the difference in liveweight gain between the treatment groups was 61 g/day over the first half of the trial and 38 g/day over the second half. Hence, the greatest impact of C. oncophora infection was evident in the younger calves (over summer) and this declined over the latter part of the study (spring), when the FECs also declined, consistent with the onset of significant immunity (Armour, 1989). In addition, in 2010, there was an apparent period of compensatory growth in the spring, where the animals previously treated with eprinomectin alone grew faster than those previously treated with the more effective combination of eprinomectin, albendazole and levamisole. Thus a liveweight difference of 15 kg between the treatment groups was reduced to12.9 kg by 23 November and this was evident in the
3.4. Faecal cultures Cooperia spp. dominated infections in all groups during the summerwinter period, after which proportions changed to become dominated by Ostertagia spp. and to a lesser extent Trichostrongylus spp. (Fig. 3). These changes in species composition coincided with the decline in FEC observed over the winter-spring in both years (Fig. 2). Immediately following the anthelmintic treatments (i.e. the treatment efficacy tests conducted twice each year) Cooperia spp. completely dominated the egg counts (i.e. 100% of faecal culture) with the exception of the second test in 2011 when 9% of the recovered L3 were Ostertagia spp. However, at this test the FEC was only 10 epg so this post-treatment recovery of Ostertagia spp. larvae is unlikely to reflect a drop in efficacy against this parasite. However, although the eprinomectin pour-on treatments were highly effective at removing Ostertagia spp. at the time of treatment, the period of persistent activity against this parasite claimed on the product label (i.e. 28 days) was not observed, with Ostertagia spp. L3 being present in cultures within 4 weeks of treatment (Fig. 3). 3.5. Pasture plucks Prior to the start of the trial all paddocks were contaminated as evenly as possible to ensure there were no differences between the farmlets or the treatments. Over the summer-autumn of 2010 there was a pattern of lower L3 numbers in treatment 2 farmlets, although these differences were not significant. However, commencing in August (winter) this pattern reversed with treatment 2 farmlets tending to have higher L3 numbers than treatment 1. This reversal of pattern in pasture contamination resulted in the treatment by time interaction being significant (p < 0.05) with two occasions where Treatment 2 had higher numbers of L3/kg DM than Treatment 1 (Fig. 4a). Despite this the average number of L3/kg DM measured across the year in Treatment 1 was 607, compared with 380 in Treatment 2. In 2011, the levels of pasture contamination tended to be lower (yearly average of 309 and 128 L3/kg DM for Treatments 1 and 2 respectively) (Fig. 4b) but neither the treatment effect, nor the treatment by time interaction, were significant. 4. Discussion The purpose of this study was to evaluate the consequences of failing to adequately control anthelmintic resistant C. oncophora in young calves by treating them with a pour-on formulation of eprinomectin. The results of the study are consistent with the conclusion that, in general, Cooperia spp. are less pathogenic than other parasites of cattle (Herlich 1965; Coop et al., 1979; Armour et al., 1987) but that in sufficient numbers they can cause production loss (Stromberg et al., 2012; Leigh and Hunnam 2013). Even though C. oncophora is regarded as less pathogenic than Cooperia punctata and Cooperia pectinata (Herlich, 1965), in the first year of this study failing to adequately control resistant C. oncophora resulted in a loss of nearly 13 kg liveweight in cattle of about 18 months of age. However, the two years of the study produced quite different results with the second year showing lower FECs, lower numbers of larvae on pasture and no difference in growth rates between the treatments compared to the first year. In this, the results were opposite to the initial hypothesis that larval numbers on pasture would increase over time (across seasons) through use of a low efficacy treatment and that this would result in increased parasite challenge and a greater production loss due to parasitism in the second year of the study. The trial site used for this study had not been grazed with cattle for many years prior to this study and so it was necessary to initially infect the site with cattle parasites. This was achieved by grazing first with untreated 18-month to 2 year old cattle which, because of their age, would be expected to have low FEC and also a low proportion of Cooperia infection (Smith and Archibald, 1968; Smith 1970; Armour 61
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Acknowledgements
statistical analysis as a significant treatment by time interaction. Concurrently, there was also a significant treatment by time interaction in Cooperia L3 numbers on herbage (p = 0.0057) indicating that after winter, in the eprinomectin alone treated groups, there were lower numbers of L3 on herbage. While FEC data was variable and showed little overall difference between treatments, we might speculate that the eprinomectin alone treated cattle experienced a greater level of exposure to parasites over the summer-winter period (as indicated by higher L3/kg herbage) which resulted in a more rapid development of immunity and an earlier reduction in FEC and lower larval numbers on pasture in the spring. This coincided with the period of more rapid growth suggesting a likely cause for the compensatory growth. The lack of an overall significant difference in FEC between the treatment groups, and the lower than expected differences in pasture L3 numbers, probably reflects the 6 week treatment interval maintained through-out the trial. The eprinomectin alone treatments failed to reduce FEC to low levels (average efficacy of 51%) and although the oral treatments were effective they lack any substantial persistent activity. Therefore, given an approximately 21-day pre-patent period after treatment and the 42-day treatment interval, considerable egg deposition on pasture would be expected for both treatments. Thus, the level of contamination of pastures in the effectively treated groups (Treatment 2) was higher than might be expected based on the consistently high efficacy achieved. It follows that if the animals had been treated at shorter intervals (e.g. 4 weekly) then the differences between the treatment groups would likely have been greater. The magnitude and pattern of liveweight gain in the two years were different (Fig. 1), with the average daily gain of the effectively treated animals being 0.78 kg/day in 2010 and 0.97 kg/day in 2011. These weight gain figures are not dissimilar to values measured in other New Zealand trials (e.g. Purchas and Grant, 1995). In 2011, the animals gained weight at a uniform rate throughout the trial whereas in 2010 weight gain was slower through summer-winter before accelerating in the spring (Fig. 1). The magnitude of the differences between the treatment groups were small compared to the difference between years, suggesting that the difference between years is unlikely to be due to parasitism. Unfortunately, pasture dry matter estimates and growth rates were not recorded, however, casual observations suggest that pasture growth rates were lower in the first half of 2010, with some supplements (hay) being fed over the winter (P. Candy, pers obs.), and this is a likely explanation for the slower growth rates of the calves over this period. In summary, the results of this study support the view that while C. oncophora is regarded as less pathogenic than other Cooperia spp. (Herlich, 1965), and the genus in general is less pathogenic than other nematodes commonly infecting cattle, failing to control resistant populations in young cattle can still result in production losses. Interestingly, the 2010 data show evidence of compensatory growth in the spring which we speculate is linked to a more rapid onset of immunity in the calves treated with an anthelmintic with low efficacy against C. oncophora. Also, the data indicates a likely low carry-over of infective L3 on pasture between crops of young calves under management typical of many New Zealand farms. In contrast to the situation in other parasites of cattle and sheep (Waghorn et al., 2006; Waghorn et al., 2016), resistance in C. oncophora is almost universal in New Zealand. This low survival of L3 from year to year, resulting in low ‘refugia’ of parasite larvae on pasture when drenching of young calves begins each summer, may help explain why resistance is so common in this parasite in New Zealand
Wendy Taylor, Barbara Adlington and Christian Sauermann assisted in the field and laboratory. Christian Sauermann and Ian Sutherland, along with two anonymous referees made helpful comments on an earlier manuscript. This work was funded by farmer levies through Beef + Lamb New Zealand under contract number 09AR03. References Armour, J., Bairden, K., Holmes, P.H., Parkins, J.J., Ploeger, H., Salman, S.K., McWilliam, P.N., 1987. Pathophysiological and parasitological studies on Cooperia oncophora infections in calves. Res. Vet. Sci. 42, 373–381. Armour, J., Bairden, K., Ryan, W.G., 1988. Immunity of ivermectin treated cattle to challenge from helminth parasites in the following season. Vet. Rec. 122, 223–225. Armour, J., 1989. The influence of host immunity on the epidemiology of trichostrongyle infections in cattle. Vet. Parasitol. 32, 5–19. Brunsdon, R.V., 1964. The incidence of gastro-intestinal nematodes in cattle in New Zealand. N. Z. Vet. J. 12, 135–139. Charlier, J., van der Voort, M., Kenyon, F., Skuce, P., Vercruysse, J., 2014. Chasing helminths and their economic impact on farmerd ruminants. Trends Parasitol. 30, 361–367. Coop, R.L., Sykes, A.R., Angus, K.W., 1979. The pathogenicity of daily intakes of Cooperia oncophora larvae in growing calves. Vet. Parasitol. 5, 261–269. Familton, A.S., 2001. Cooperia in cattle in New Zealand. Proc. of the 31st Seminar, Soc. Sheep and Beef Cattle Vet N. Z. Vet. Assoc 99–109. Fazzio, L.E., Sánchez, R.O., Streitenberger, N., Galvan, W.R., Giudici, C.J., Gimeno, E.J., 2014. The effect of anthelmintic resistance on the productivity in feedlot cattle. Vet. Parasitol. 206, 240–245. Hawkins, J.A., 1993. Economic benefits of parasite control in cattle. Vet. Parasitol. 46, 159–173. Herlich, H., 1965. The effects of the intestinal worms, Cooperia pectinata and Cooperia oncophora: on experimentally infected calves. American J. Vet. Res. 26, 1032–1036. Jackson, R., Rhodes, A.P., Pomroy, W.E., Leathwick, D.M., West, D.M., Waghorn, T.S., Moffat, J.R., 2006. Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand. N. Z. Vet. J. 54, 289–296. Leathwick, D.M., Miller, C.M., 2013. Efficacy of oral, injectable and pour-on formulations of moxidectin against gastrointestinal nematodes in cattle in New Zealand. Vet. Parasitol. 191, 293–300. Leigh, J., Hunnam, J., 2013. The effect of ML resistant Cooperia in healthy cattle. Proc. of the 43rd Seminar, Soc. Sheep and Beef Cattle Vet N. Z. Vet. Assoc. 247–251. Louvandini, H., Rodriques, R.R., Gennari, S.M., McManus, C.M., Vitti, D.M.S.S., 2009. Phosphorus kinetics in calves experimentally submitted to a trickle infection with Cooperia punctata. Vet. Parasitol. 163, 47–51. Lyndal-Murphy, M., 1993. Anthelmintic resistance in sheep. In: Corner, L.A., Bagust, T.J. (Eds.), Australian Standard Diagnostic Techniques for Animal Diseases. CSIRO Melbourne, Australia, pp. 1–17. Mason, P.C., McKay, C.H., 2006. Field studies investigating anthelmintic resistance in young cattle on five farms in New Zealand. N. Z. Vet. J. 54, 318–322. Miller, C.M., Waghorn, T.S., Leathwick, D.M., Candy, P.M., Oliver, A.-M.B., Watson, T.G., 2012. The production cost of anthelmintic resistance in lambs. Vet. Parasitol. 186, 376–381. Purchas, R.W., Grant, D.A., 1995. Liveweight gain and carcass characteristics of bulls and steers farmed on hill country. N. Z. J. Agric. Res. 38, 131–142. Sauermann, C.W., Leathwick, D.M., 2018. A climate-driven model for the dynamics of the free-living stages of Cooperia oncophora. Vet. Parasitol Vetpar-17-11844. Smith, H.J., Archibald, R.M., 1968. The effects of age and previous infection on the development of gastrointestinal parasitism in cattle. Canadian J. Comp. Med. 32, 511–517. Smith, H.J., 1970. On the development of gastrointestinal parasitism in bovine yearlings. Canadian J. Comp. Med. 34, 303–308. Stromberg, B.E., Gasbarre, L.C., Waite, A., Bechtol, D.T., Brown, M.S., Robinson, N.A., Olson, E.J., Newcomb, H., 2012. Cooperia punctata: Effect on cattle productivity? Vet. Parasitol 183, 284–291. Sutherland, I., Scott, I., 2010. Nematode parasites. Gastrointestinal Nematiodes of Sheep and Cattle − Biology and Control. Blackwell Publishing Oxford. Sutherland, I.A., Bailey, J., Shaw, R.J., 2010. The production costs of anthelmintic resistance in sheep managed within a monthly preventive drench program. Vet. Parasitol. 171, 300–304. Waghorn, T.S., Leathwick, D.M., Rhodes, A.P., Jackson, R., Pomroy, W.E., West, D.M., Moffat, J.R., 2006. Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand. N. Z. Vet. J. 54, 278–282. Waghorn, T.S., Miller, C.M., Leathwick, D.M., 2016. Confirmation of ivermectin resistance in Ostertagia ostertagi in cattle in New Zealand. Vet. Parasitol. 229, 139–143.
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Veterinary Parasitology journal homepage: www.elsevier.com/locate/vetpar
Research paper
The effect on liveweight gain of using anthelmintics with incomplete efficacy against resistant Cooperia oncophora in cattle Paul M. Candy, Tania S. Waghorn, Chris M. Miller, Siva Ganesh, Dave M. Leathwick
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AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston North, 4442, New Zealand
A R T I C L E I N F O
A B S T R A C T
Keywords: Cattle Cooperia Anthelmintic resistance Productivity loss
A replicated field trial was conducted to measure the effect on liveweight gain of failing to adequately control anthelmintic resistant populations of Cooperia oncophora and to determine whether populations, and hence production losses, increased with time. Eight mobs of 10 Friesian-Hereford calves were run on independent farmlets from January to December, over each of two years. All mobs were routinely treated with a pour-on formulation of eprinomectin every six weeks, which controlled parasites other than Cooperia. Four mobs also received six weekly treatments with an oral levamisole plus albendazole combination anthelmintic to control Cooperia. Liveweights, condition scores, faecal egg counts and larval numbers on pasture were measured throughout. In the first year animals treated with eprinomectin alone were 12.9 kg lighter in November than those treated with eprinomectin plus albendazole and levamisole, however, in the second year there was no difference between the treatment groups. The data, therefore, support the view that while C. oncophora is less pathogenic than other cattle parasite species it can still cause production losses when present in sufficient numbers. In the first year of the study, parasite load, as measured by faecal nematode egg count and larval numbers on herbage, tended to be higher and calf growth rates lower than in the second year. In both years, counts of infective larvae on herbage declined over winter–spring to be at low levels before mid-summer. This suggests that the carry-over of infection from one crop of calves to the next was relatively small and hence that the level of challenge to the young calves at the start of each year was largely due to the effectiveness of the quarantine treatments administered when the animals arrived on the trial site. Low survival of larvae on pasture between grazing seasons, resulting in small larval populations on pasture when drenching programmes start each summer, might help to explain the widespread development of anthelmintic resistance in this parasite under New Zealand grazing systems.
1. Introduction Internal parasites are regarded as an important production limiting factor by a majority of New Zealand cattle farmers (Jackson et al., 2006). The recent emergence of anthelmintic resistance in pathogenic species such as Ostertagia ostertagi (Waghorn et al., 2016) is certain to enhance this view, and is a potentially serious future problem for the cattle industry. The cost of covert (undetected) resistance in parasites of sheep has been estimated at up to 14% of lamb carcass value (Sutherland et al., 2010; Miller et al., 2012), but equivalent estimates for cattle have not previously been determined. In New Zealand, Cooperia spp. dominate infections in cattle under 12–18 months of age. Cooperia oncophora resistant to the macrocyclic lactone (ML) class of anthelmintics are present on almost every farm in the country (Mason and McKay, 2006; Waghorn et al., 2006; Leathwick
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and Miller, 2013) and many of these populations are also resistant to benzimidazole anthelmintics (Waghorn et al., 2006). Despite this many New Zealand farmers continue to use single action ML products (Jackson et al., 2006) and most use pour-on formulations which are unlikely to deliver high efficacy against C. oncophora (Leathwick and Miller, 2013). The continued use of these products is likely to reflect the perception, held by most New Zealand cattle farmers, that anthelmintic resistance is not a significant animal health issue (Jackson et al., 2006). Consequently, many farmers are likely to be failing to control C. oncophora on their farms, and presumably they continue to do this because they see no indication of parasitism in the treated animals. While it is generally considered that Cooperia spp. are of secondary importance as parasites of cattle (Brunsdon, 1964; Familton, 2001; Sutherland and Scott, 2010) there is evidence that infection can result in detrimental effects on animal growth (Coop et al., 1979; Stromberg
Corresponding author. E-mail address: [email protected] (D.M. Leathwick).
https://doi.org/10.1016/j.vetpar.2017.12.023 Received 2 October 2017; Received in revised form 29 December 2017; Accepted 29 December 2017 0304-4017/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Mean ( ± 95% CI) liveweights for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines).
consisted of 5 paddocks, one from each cluster, which ensured that none of the paddocks within a farmlet were adjacent to each other and minimised the chances that any underlying pattern in the soil or pasture could influence the response to treatment. Each farmlet was randomly allocated to one of two treatments. Hence, eight farmlets, each of approximately 3 ha, were established in two complete replicate blocks of four, with the four farmlets within each block allocated to two replicates of two treatments. Prior to the commencement of this trial the site was grazed with untreated 18–24 month-old cattle for several months in order to contaminate the site with cattle parasites, as previously it had been grazed exclusively with sheep for many years.
et al., 2012; Leigh and Hunnam, 2013). Part of the explanation for this apparent contradiction may lie in the levels of challenge to which cattle are exposed. Logically, continued use of a less than fully effective anthelmintic will result in increased levels of pasture contamination and subsequently the number of larvae ingested by grazing livestock. Thus, long-term use of single-active ML products might be expected to result in an accumulation of infective Cooperia spp. larvae on pasture and an increased impact on animal performance. Hence, a parasite with low inherent pathogenicity may have a greater impact as the numbers to which a host is exposed increase. The current study was, therefore, instigated to quantify the effect on liveweight gain of failing to adequately control C. oncophora by using single action ML pour-ons against a resistant worm population, and to determine whether this increased over time through any accumulation of larvae on pasture.
2.1. Animals In January 2010, 80 newly weaned Friesian-Hereford cross calves were purchased at a commercial stock sale and transported to the farm. These animals were selected based on their uniformity of breed, size and condition, with no consideration given to their farm of origin or the anthelmintic resistance status of any parasites they may be infected with i.e. it was assumed that they would have a parasite infection and that any C. oncophora they were infected with would be largely resistant to ML anthelmintics. On their arrival at the research farm all calves were administered an oral dose of 0.2 mg/kg ivermectin (Ivomec, Merial Ancare New Zealand Limited, Auckland, New Zealand) which removed all parasite species except C. oncophora (mean post-treatment FEC was 128 eggs per g faeces (epg) and cultures were 96% Cooperia
2. Methods A replicated field study was conducted on the Flock House Research farm near Bulls in the Manawatu region of the North Island of New Zealand, from January 2010 to December 2011. An area of approximately 24 ha was initially divided into 2 replicate blocks before each of these was divided into 20 adjacent paddocks which were grouped into 5 ‘clusters’ of 4. The four paddocks within each cluster were then randomly allocated to one of four ‘farmlets’, a farmlet being a self-contained suite of paddocks carrying one group of animals and a single discrete worm population. Each farmlet, therefore, 57
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Fig. 2. Geometric mean ( ± 95% CI) faecal nematode egg counts (eggs per gram) for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines). Treatment dates were 2 Feb., 18 Mar., 27 Apr., 8 Jun., and 19 Jul in 2010 and 1 Feb., 16 Mar., 28 Apr., 14 Jun., and 26 Jul. in 2011.
Zealand) at the manufacturer’s recommended dose rate of 0.5 mg/kg liveweight, administered along the backline of each animal from shoulder to rump. In addition, Treatment 2 calves were also administered an oral dose of a combination anthelmintic delivering 7.5 mg levamisole and 10 mg albendazole per kg liveweight (Arrest C; Merial Ancare New Zealand Limited, Auckland, New Zealand). All anthelmintic doses were calculated based on the heaviest calf in each group at the time of treatment.
spp. and 4% Ostertagia spp.) The animals were then rotationally grazed over all trial paddocks on daily shifts in order to further contaminate the site prior to the trial commencing in February. At the commencement of the trial the calves were randomly allocated on the basis of liveweight into eight groups of 10 and each of these groups was randomly assigned to a farmlet where they were rotationally grazed around their respective suite of paddocks on approximately twice weekly shifts. In year 2, a similar process of purchasing animals was followed except that in order to prevent the introduction of additional parasites, all introduced calves were treated orally with a combination anthelmintic delivering 8.0 mg/kg levamisole, 4.5 mg/kg oxfendazole and 0.2 mg/kg abamectin (Matrix C; Merial Ancare New Zealand Limited, Auckland, New Zealand). Ten random FECs collected 10 days after this treatment were all zero.
2.3. Faecal nematode egg counts (FEC) Infection levels in the calves were monitored using FEC, at approximately three to six weekly intervals, including on the day they received each of their anthelmintic treatments. Faeces collected per rectum was placed in individually labelled plastic screw-top containers and returned to the laboratory for processing. The number of strongylid eggs present in a 4 g subsample was determined using a modified McMaster method in which each egg counted represented 25 epg (Lyndal-Murphy, 1993). Any faecal material remaining after each collection was pooled by group and cultured at 22 °C for 14 days to produce infective third stage larvae (L3) for identification. These were extracted from the culture material by baermannisation, concentrated by sedimentation in water at 10 °C, and identified to genus. Ten to 14 days after the second (March) and fifth (July) anthelmintic treatments in Year 1, and the first (February) and fifth (July) treatments in Year 2, calves were resampled for FEC, in order to
2.2. Treatment structure The treatment structure consisted of two treatments with four replicates of each. All calves received a programme of five anthelmintic treatments at 42-day intervals (the eprinomectin product label claims persistent activity against Cooperia and Ostertagia spp. of 21 and 28 days, respectively, and states that treatment intervals of up to 56 days should be effective at controlling these species), commencing in February each year. All calves were treated with eprinomectin (Ivomec Eprinex Pour on; Merial Ancare New Zealand Limited, Auckland, New 58
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Fig. 3. The percentage ( ± 95% CI) of infective third stage larvae (L3) recovered from faecal cultures in A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pour-on plus an albendazole + levamisole combination oral drench (dashed lines), and square symbols represent Cooperia spp. and circles represent Ostertagia spp. Diamonds indicate samples collected 10–14 days after treatment.
with one experimental factor (2 Treatments) and one repeated factor (5 Weeks). Animals were therefore treated as genuine replications. Linear mixed effects models were utilized with ‘Animal’ as a random effect to capture appropriate structure for ANOVA. Replicate (the two replicate blocks) was included as a fixed effect. When the interaction and/or main effects in the ANOVA was significant (p-value < 0.05), the nature of these effects was investigated using pairwise comparisons of the treatment means. For the 2010 liveweights, data were transformed by square root in order to satisfy the assumptions for the ANOVA, however, in 2011 no transformation was required. In both years the liveweight of the calves at the beginning of the trial (February) was included in the model as a covariate. For analysis of FEC the counts taken soon after treatment to measure efficacy were removed from the analysis because these contained large numbers of zeros. The remaining data were transformed by Log10 + 1 prior to analysis. For comparison of pasture larval infestations (i.e. L3/kg DM) repeated measures ANOVA was used with two treatments and 11 repeated measurements. Because only some paddocks were sampled and the experimental unit was the worm population, farmlets were used as genuine replicates and the data from the paddocks within the farmlets were averaged. In both years the counts of L3/kg DM were transformed by Log10 +1 to meet the assumptions for ANOVA.
measure the efficacy of the treatment. Efficacy was estimated by comparing the pre- and post-treatment mean FEC for each group of calves, and calculating the percentage reduction in undifferentiated FEC. Also, efficacy against the main parasite genera was calculated after partitioning the total FEC based on the proportion of each genus recovered from the corresponding faecal culture. 2.4. Parasite larvae on pasture Pasture samples (‘plucks’) were taken from one paddock within each farmlet at irregular intervals from January to December, with additional paddocks in each farmlet being sampled in late autumn (May) and late spring (November) each year. Samples were collected by plucking pasture between the thumb and index finger while walking transects across a paddock. A minimum of 300 g of pasture, made up of 200–300 plucks from a single paddock, constituted one sample. Samples were soaked in water plus detergent overnight and the L3 were concentrated by sedimentation. After settling overnight at 4 °C, the water containing L3 was siphoned down to 10 ml and the larvae identified to genus and counted. 2.5. Statistics For measurements where the experimental unit was an individual animal (i.e. liveweight and FEC) a repeated measures ANOVA was used, 59
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Fig. 4. Pasture pluck results (mean L3/kg DM ± 95% CI) for A, 2010 and B, 2011 when calves were treated 5 times at 6 weekly intervals with either eprinomectin pour-on (solid lines) or eprinomectin pouron plus an albendazole + levamisole combination oral drench (dashed lines).
3. Results
difference of 15 kg on 1 September (p < 0.005) (Fig. 1a). However, after that the liveweights converged somewhat with a final liveweight difference of 12.9 kg (p < 0.06). Six of the last eight liveweight comparisons were significantly different (p < 0.05) or approached significance (p < 0.072). In 2011, the liveweights remained similar throughout the trial with no significant difference between the treatment groups (Fig. 1b). Noticeably, the weight gains in the two years were quite different with the final (December) liveweights being 346 kg and 429 kg in 2010 and 2011, respectively.
3.1. Treatment efficacy As expected the efficacy of the two treatments was different. Treatment 2 (eprinomectin + levamisole + albendazole) consistently achieved high efficacy, averaging 98.5% (range 97%–100%) faecal egg count reduction over the duration of the trial. In contrast, Treatment 1, the eprinomectin alone averaged only 51% (range 27%-79%) reduction in FEC. Larval identification from faecal cultures collected after treatment indicated that Cooperia was the dominant (> 95%) genus surviving treatment. Calculating efficacy after partitioning of FECs to genera based on the proportions recovered from the faecal cultures showed that efficacy of all treatments against Ostertagia spp. and Trichostrongylus spp. exceeded 98%. Similarly, efficacy of treatment 2 (the combination of three actives) against Cooperia spp. exceeded 97% in all cases. Efficacy of the eprinomectin alone against Cooperia spp. ranged from 18% to 73%.
3.3. FEC Despite the differences in efficacy of the anthelmintic treatments, the faecal egg counts outside of the post-treatment intervals (i.e. the 3–4 weeks after treatment) were not that different (Fig. 2). In 2010, the treatment effect had a p-value of 0.098 but the interaction with time was highly significant (p < 0.0001), indicating that there was a different pattern of FEC between the treatments over time (Fig. 2a). The paired comparisons indicated that on some occasions both treatment groups had similar FECs, on two occasions (July and November) Treatment 2 FECs were lower and on one occasion (June) Treatment 2 FECs were higher than Treatment 1 FECs. In 2011, the FECs overall tended to be lower than in 2010, and there were no differences between the Treatment groups (Fig. 2).
3.2. Liveweight At the commencement of the trial in each year, calf liveweights were similar by virtue of the randomisation to group i.e. liveweights were used to allocate animals to farmlet and treatment so they would be expected to be similar. In 2010 average liveweight between the two treatments progressively diverged with time, reaching a maximum 60
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et al., 1988; Armour 1989). In addition, when the trial calves were brought onto the site they were initially treated only with ivermectin, which did not entirely remove the C. oncophora infections. The mean FEC of these calves, after the ivermectin treatment, was 128 epg (96% Cooperia spp.). With only a short period of grazing by these calves before the trial started, it might reasonably be expected that the numbers of Cooperia spp. L3 on pasture would have been relatively low, and that numbers would have built up with time, especially in the eprinomectin only groups which failed to reduce faecal egg output to low levels. In both years, FECs initially rose in both treatment groups over the summer-autumn period, indicating that the calves were picking up ongoing infection. However, FECs then declined through the winter to be low in both treatment groups by spring (September). Similarly, L3 numbers on pasture also increased initially but then declined relatively quickly to be at low levels at the end of spring-early summer (Fig. 4). Thus, there appeared to be little carry-over of pasture larval infestations from autumn-winter to the following spring-summer with, in both years, L3 numbers declining to low levels before the introduction of new season calves in January-February. It seems likely therefore that the higher levels of pasture contamination in the first year compared to the second year was a direct result of the effectiveness of the quarantine treatments given to the trial calves on their arrival. In the first year, an ineffective treatment was given deliberately in order to ensure contamination of the pastures with resistant Cooperia. This was confirmed by positive egg counts in the calves after treatment. In contrast, in the second year, this quarantine treatment was a combined treatment with abamectin, levamisole and oxfendazole, given to prevent the introduction of any additional parasites, and the effectiveness of this treatment was confirmed by the absence of eggs in the FEC. Given the apparent low level of persistence of the L3 population on pasture between grazing seasons, this suggests that the challenge facing the young calves each summer was largely determined by the efficacy of the quarantine treatment. Further work, supporting this interpretation of the data can be found in Sauermann and Leathwick (2018). There is little doubt that gastro-intestinal nematodes are capable of causing significant production losses in cattle (Hawkins 1993; Charlier et al., 2014), however, the specific role of Cooperia species is less clear. Artificial challenge experiments (Coop et al., 1979; Louvandini et al., 2009) along with productivity studies in feedlots (Stromberg et al., 2012; Fazzio et al., 2014) and with animals grazing pasture (Leigh and Hunnam 2013) indicate that Cooperia infection can result in reduced feed intake, impaired metabolism and reduced growth rates. The magnitude of the reduced growth rates attributable as a result of infection with Cooperia, irrespective of the species involved, are not high in any of these studies, ranging from 87 to 121 g/day. In the current study differences in growth were lower than these values, averaging only 47 g/day in 2010 and close to zero in 2011. However, the periods over which measurements were made differed considerably between studies, from 250 to 300 days in the current study to only 40–65 days in the earlier ones. The longer time period encompassed a period after which the animals would have been expected to have developed significant immunity to Cooperia infection (Armour, 1989) and this was reflected in a lesser effect of infection i.e. in 2010 the difference in liveweight gain between the treatment groups was 61 g/day over the first half of the trial and 38 g/day over the second half. Hence, the greatest impact of C. oncophora infection was evident in the younger calves (over summer) and this declined over the latter part of the study (spring), when the FECs also declined, consistent with the onset of significant immunity (Armour, 1989). In addition, in 2010, there was an apparent period of compensatory growth in the spring, where the animals previously treated with eprinomectin alone grew faster than those previously treated with the more effective combination of eprinomectin, albendazole and levamisole. Thus a liveweight difference of 15 kg between the treatment groups was reduced to12.9 kg by 23 November and this was evident in the
3.4. Faecal cultures Cooperia spp. dominated infections in all groups during the summerwinter period, after which proportions changed to become dominated by Ostertagia spp. and to a lesser extent Trichostrongylus spp. (Fig. 3). These changes in species composition coincided with the decline in FEC observed over the winter-spring in both years (Fig. 2). Immediately following the anthelmintic treatments (i.e. the treatment efficacy tests conducted twice each year) Cooperia spp. completely dominated the egg counts (i.e. 100% of faecal culture) with the exception of the second test in 2011 when 9% of the recovered L3 were Ostertagia spp. However, at this test the FEC was only 10 epg so this post-treatment recovery of Ostertagia spp. larvae is unlikely to reflect a drop in efficacy against this parasite. However, although the eprinomectin pour-on treatments were highly effective at removing Ostertagia spp. at the time of treatment, the period of persistent activity against this parasite claimed on the product label (i.e. 28 days) was not observed, with Ostertagia spp. L3 being present in cultures within 4 weeks of treatment (Fig. 3). 3.5. Pasture plucks Prior to the start of the trial all paddocks were contaminated as evenly as possible to ensure there were no differences between the farmlets or the treatments. Over the summer-autumn of 2010 there was a pattern of lower L3 numbers in treatment 2 farmlets, although these differences were not significant. However, commencing in August (winter) this pattern reversed with treatment 2 farmlets tending to have higher L3 numbers than treatment 1. This reversal of pattern in pasture contamination resulted in the treatment by time interaction being significant (p < 0.05) with two occasions where Treatment 2 had higher numbers of L3/kg DM than Treatment 1 (Fig. 4a). Despite this the average number of L3/kg DM measured across the year in Treatment 1 was 607, compared with 380 in Treatment 2. In 2011, the levels of pasture contamination tended to be lower (yearly average of 309 and 128 L3/kg DM for Treatments 1 and 2 respectively) (Fig. 4b) but neither the treatment effect, nor the treatment by time interaction, were significant. 4. Discussion The purpose of this study was to evaluate the consequences of failing to adequately control anthelmintic resistant C. oncophora in young calves by treating them with a pour-on formulation of eprinomectin. The results of the study are consistent with the conclusion that, in general, Cooperia spp. are less pathogenic than other parasites of cattle (Herlich 1965; Coop et al., 1979; Armour et al., 1987) but that in sufficient numbers they can cause production loss (Stromberg et al., 2012; Leigh and Hunnam 2013). Even though C. oncophora is regarded as less pathogenic than Cooperia punctata and Cooperia pectinata (Herlich, 1965), in the first year of this study failing to adequately control resistant C. oncophora resulted in a loss of nearly 13 kg liveweight in cattle of about 18 months of age. However, the two years of the study produced quite different results with the second year showing lower FECs, lower numbers of larvae on pasture and no difference in growth rates between the treatments compared to the first year. In this, the results were opposite to the initial hypothesis that larval numbers on pasture would increase over time (across seasons) through use of a low efficacy treatment and that this would result in increased parasite challenge and a greater production loss due to parasitism in the second year of the study. The trial site used for this study had not been grazed with cattle for many years prior to this study and so it was necessary to initially infect the site with cattle parasites. This was achieved by grazing first with untreated 18-month to 2 year old cattle which, because of their age, would be expected to have low FEC and also a low proportion of Cooperia infection (Smith and Archibald, 1968; Smith 1970; Armour 61
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Acknowledgements
statistical analysis as a significant treatment by time interaction. Concurrently, there was also a significant treatment by time interaction in Cooperia L3 numbers on herbage (p = 0.0057) indicating that after winter, in the eprinomectin alone treated groups, there were lower numbers of L3 on herbage. While FEC data was variable and showed little overall difference between treatments, we might speculate that the eprinomectin alone treated cattle experienced a greater level of exposure to parasites over the summer-winter period (as indicated by higher L3/kg herbage) which resulted in a more rapid development of immunity and an earlier reduction in FEC and lower larval numbers on pasture in the spring. This coincided with the period of more rapid growth suggesting a likely cause for the compensatory growth. The lack of an overall significant difference in FEC between the treatment groups, and the lower than expected differences in pasture L3 numbers, probably reflects the 6 week treatment interval maintained through-out the trial. The eprinomectin alone treatments failed to reduce FEC to low levels (average efficacy of 51%) and although the oral treatments were effective they lack any substantial persistent activity. Therefore, given an approximately 21-day pre-patent period after treatment and the 42-day treatment interval, considerable egg deposition on pasture would be expected for both treatments. Thus, the level of contamination of pastures in the effectively treated groups (Treatment 2) was higher than might be expected based on the consistently high efficacy achieved. It follows that if the animals had been treated at shorter intervals (e.g. 4 weekly) then the differences between the treatment groups would likely have been greater. The magnitude and pattern of liveweight gain in the two years were different (Fig. 1), with the average daily gain of the effectively treated animals being 0.78 kg/day in 2010 and 0.97 kg/day in 2011. These weight gain figures are not dissimilar to values measured in other New Zealand trials (e.g. Purchas and Grant, 1995). In 2011, the animals gained weight at a uniform rate throughout the trial whereas in 2010 weight gain was slower through summer-winter before accelerating in the spring (Fig. 1). The magnitude of the differences between the treatment groups were small compared to the difference between years, suggesting that the difference between years is unlikely to be due to parasitism. Unfortunately, pasture dry matter estimates and growth rates were not recorded, however, casual observations suggest that pasture growth rates were lower in the first half of 2010, with some supplements (hay) being fed over the winter (P. Candy, pers obs.), and this is a likely explanation for the slower growth rates of the calves over this period. In summary, the results of this study support the view that while C. oncophora is regarded as less pathogenic than other Cooperia spp. (Herlich, 1965), and the genus in general is less pathogenic than other nematodes commonly infecting cattle, failing to control resistant populations in young cattle can still result in production losses. Interestingly, the 2010 data show evidence of compensatory growth in the spring which we speculate is linked to a more rapid onset of immunity in the calves treated with an anthelmintic with low efficacy against C. oncophora. Also, the data indicates a likely low carry-over of infective L3 on pasture between crops of young calves under management typical of many New Zealand farms. In contrast to the situation in other parasites of cattle and sheep (Waghorn et al., 2006; Waghorn et al., 2016), resistance in C. oncophora is almost universal in New Zealand. This low survival of L3 from year to year, resulting in low ‘refugia’ of parasite larvae on pasture when drenching of young calves begins each summer, may help explain why resistance is so common in this parasite in New Zealand
Wendy Taylor, Barbara Adlington and Christian Sauermann assisted in the field and laboratory. Christian Sauermann and Ian Sutherland, along with two anonymous referees made helpful comments on an earlier manuscript. This work was funded by farmer levies through Beef + Lamb New Zealand under contract number 09AR03. References Armour, J., Bairden, K., Holmes, P.H., Parkins, J.J., Ploeger, H., Salman, S.K., McWilliam, P.N., 1987. Pathophysiological and parasitological studies on Cooperia oncophora infections in calves. Res. Vet. Sci. 42, 373–381. Armour, J., Bairden, K., Ryan, W.G., 1988. Immunity of ivermectin treated cattle to challenge from helminth parasites in the following season. Vet. Rec. 122, 223–225. Armour, J., 1989. The influence of host immunity on the epidemiology of trichostrongyle infections in cattle. Vet. Parasitol. 32, 5–19. Brunsdon, R.V., 1964. The incidence of gastro-intestinal nematodes in cattle in New Zealand. N. Z. Vet. J. 12, 135–139. Charlier, J., van der Voort, M., Kenyon, F., Skuce, P., Vercruysse, J., 2014. Chasing helminths and their economic impact on farmerd ruminants. Trends Parasitol. 30, 361–367. Coop, R.L., Sykes, A.R., Angus, K.W., 1979. The pathogenicity of daily intakes of Cooperia oncophora larvae in growing calves. Vet. Parasitol. 5, 261–269. Familton, A.S., 2001. Cooperia in cattle in New Zealand. Proc. of the 31st Seminar, Soc. Sheep and Beef Cattle Vet N. Z. Vet. Assoc 99–109. Fazzio, L.E., Sánchez, R.O., Streitenberger, N., Galvan, W.R., Giudici, C.J., Gimeno, E.J., 2014. The effect of anthelmintic resistance on the productivity in feedlot cattle. Vet. Parasitol. 206, 240–245. Hawkins, J.A., 1993. Economic benefits of parasite control in cattle. Vet. Parasitol. 46, 159–173. Herlich, H., 1965. The effects of the intestinal worms, Cooperia pectinata and Cooperia oncophora: on experimentally infected calves. American J. Vet. Res. 26, 1032–1036. Jackson, R., Rhodes, A.P., Pomroy, W.E., Leathwick, D.M., West, D.M., Waghorn, T.S., Moffat, J.R., 2006. Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand. N. Z. Vet. J. 54, 289–296. Leathwick, D.M., Miller, C.M., 2013. Efficacy of oral, injectable and pour-on formulations of moxidectin against gastrointestinal nematodes in cattle in New Zealand. Vet. Parasitol. 191, 293–300. Leigh, J., Hunnam, J., 2013. The effect of ML resistant Cooperia in healthy cattle. Proc. of the 43rd Seminar, Soc. Sheep and Beef Cattle Vet N. Z. Vet. Assoc. 247–251. Louvandini, H., Rodriques, R.R., Gennari, S.M., McManus, C.M., Vitti, D.M.S.S., 2009. Phosphorus kinetics in calves experimentally submitted to a trickle infection with Cooperia punctata. Vet. Parasitol. 163, 47–51. Lyndal-Murphy, M., 1993. Anthelmintic resistance in sheep. In: Corner, L.A., Bagust, T.J. (Eds.), Australian Standard Diagnostic Techniques for Animal Diseases. CSIRO Melbourne, Australia, pp. 1–17. Mason, P.C., McKay, C.H., 2006. Field studies investigating anthelmintic resistance in young cattle on five farms in New Zealand. N. Z. Vet. J. 54, 318–322. Miller, C.M., Waghorn, T.S., Leathwick, D.M., Candy, P.M., Oliver, A.-M.B., Watson, T.G., 2012. The production cost of anthelmintic resistance in lambs. Vet. Parasitol. 186, 376–381. Purchas, R.W., Grant, D.A., 1995. Liveweight gain and carcass characteristics of bulls and steers farmed on hill country. N. Z. J. Agric. Res. 38, 131–142. Sauermann, C.W., Leathwick, D.M., 2018. A climate-driven model for the dynamics of the free-living stages of Cooperia oncophora. Vet. Parasitol Vetpar-17-11844. Smith, H.J., Archibald, R.M., 1968. The effects of age and previous infection on the development of gastrointestinal parasitism in cattle. Canadian J. Comp. Med. 32, 511–517. Smith, H.J., 1970. On the development of gastrointestinal parasitism in bovine yearlings. Canadian J. Comp. Med. 34, 303–308. Stromberg, B.E., Gasbarre, L.C., Waite, A., Bechtol, D.T., Brown, M.S., Robinson, N.A., Olson, E.J., Newcomb, H., 2012. Cooperia punctata: Effect on cattle productivity? Vet. Parasitol 183, 284–291. Sutherland, I., Scott, I., 2010. Nematode parasites. Gastrointestinal Nematiodes of Sheep and Cattle − Biology and Control. Blackwell Publishing Oxford. Sutherland, I.A., Bailey, J., Shaw, R.J., 2010. The production costs of anthelmintic resistance in sheep managed within a monthly preventive drench program. Vet. Parasitol. 171, 300–304. Waghorn, T.S., Leathwick, D.M., Rhodes, A.P., Jackson, R., Pomroy, W.E., West, D.M., Moffat, J.R., 2006. Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand. N. Z. Vet. J. 54, 278–282. Waghorn, T.S., Miller, C.M., Leathwick, D.M., 2016. Confirmation of ivermectin resistance in Ostertagia ostertagi in cattle in New Zealand. Vet. Parasitol. 229, 139–143.
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