The effect of a metaphylactic treatment with diclazuril (Vecoxan) on the oocyst excretion and growth performance of calves exposed to a natural Eimeria infection.

A multicenter field efficacy study was performed in six farms located in Belgium, France and Germany with a history of suspected coccidiosis outbreaks and the proven presence of Eimeria bovis and/or Eimeria zuernii. At each of these trial sites the calves were randomly allocated to two groups (T, treated; C, control) of similar size. In total, 231 calves were included in the study. Group T calves (n=116) were drenched with a single dose of diclazuril (Vecoxan, 1mg/kg body weight) close to the time of expected outbreak of coccidiosis (day 1 of the study period), group C calves (n=115) served as placebo-treated controls. Although E. bovis and/or E. zuernii were identified at all trial sites, clinical coccidiosis was only noted in 16% of the group C calves. At day 5 of the study period (4 days after treatment), faecal oocyst counts (opg, oocysts per gram) were substantially lower in group T ("short-term effect") compared to group C. At four trial sites, the respective values of groups T and C were significantly different (P=0.0132 to P=0.0001) in favour of group T. For the pooled data of all trial sites, this effect was highly significant (P<0.0001). The overall faecal oocyst counts from day 3 until day 21 of the study period ("Area Under the Curve") was significantly reduced in group T by 87.2-99.5% ("long-term effect") at five trial sites (P=0.0139 to P<0.0001). The pooled data revealed a highly significant effect of treatment on oocyst excretion over the observation period (P<0.0001). On five of the six trial sites, the average weight gain was higher in group T than in group C. On those trial sites, the average weight gain of group T calves exceeded that of the controls by 95-268g/day and by 2.0-6.0kg over the study period. This effect was statistically significant (P<0.01) at one trial site. Altogether the calves of group T gained on average 129g more weight daily than the controls (+2.7kg over the study period). For these pooled data, statistical analysis confirmed the positive effect of treatment of calves exposed to coccidiosis on growth performance (P=0.003). In conclusion, metaphylactic treatment with diclazuril efficiently controls coccidiosis in calves thus reducing environmental contamination with oocysts and preventing negative effects of natural exposure to coccidiosis on growth performance of calves.

Development of a copro-antigen capture ELISA for detecting Ostertagia ostertagi infections in cattle.

The present study reports on the development of a copro-antigen capture ELISA for detecting Ostertagia ostertagi infections in cattle. The ELISA was based on polyclonal rabbit antibodies, which recognize O. ostertagi excretory/secretory antigens (ES). ES antigens are released by the metabolic active stages of the parasite in the abomasum, and passed in the faeces of the host. The detection limit of pure ES material was 30 ng ml(-1) in sample buffer and 125 ng ml(-1) in faecal extract. The test was evaluated using a follow up from six artificially infected calves. Elevated levels of Ostertagia coproantigens could be measured from 21 days after infection, indicating that only the presence of adult parasites can be detected. To evaluate the capacity of the assay to measure levels of infection, three groups of cattle were tested: 38 artificially infected calves, 17 naturally infected first grazing season calves and 16 naturally infected adult dairy cows. Optical densities were significantly correlated to the worm burdens of the animals and the ELISA had an overall sensitivity of 91% and a specificity of 45%. The test gave negative readings for faeces of animals carrying patent mono-infections with Cooperia oncophora.

Nematode parasitism in adult dairy cows in Belgium.

Over a period of 1 year, from November 1997 to October 1998, the abomasa, blood and faecal samples of 121 dairy cows in Belgium were collected and examined for nematode infections. Nematodes were present in the abomasa of 110 animals. Ostertagia was found in all 110, Trichostrongylus was seen in 65 and Haemonchus in 14 abomasa. Overall, 91% of all trichostrongyles recovered were Ostertagia. The geometric mean total number of Ostertagia was 2750, with an average of 74% inhibited early fourth stage larvae (EL4). Between November and February >90% of the Ostertagia worm burden were EL4 stages. The majority of the animals (56%) harboured a low Ostertagia burden (100-5000) and 15% had a high burden (>10,000). Sixty-four percent of the coprocultures were positive and the genera recovered were Ostertagia sp. (100%), Trichostrongylus sp. (42%), Oesophagostomum (32%), Haemonchus sp. (29%) and Cooperia sp. (16%). A seasonal pattern was evident for serum Ostertagia-specific antibodies and for serum pepsinogen concentration, with the highest levels during the summer, and low values during the winter. Dictyocaulus viviparus specific antibodies were detected in the serum of eight (7%) animals.

Nematode parasites of adult dairy cattle in the Netherlands.

Abomasa, blood samples and faecal samples for examination of nematode infections were collected from 125 dairy cows during the period November 1997-October 1998. Of these, 12 had no grazing history and were, therefore, excluded from this study. From the remaining 113, 88.5% had nematode eggs in the faeces. Larval identification of the positive cultures showed that Ostertagia spp. larvae were most frequent (97%), followed by Trichostrongylus spp. (29%), Oesophagostomum spp. (23%), Cooperia punctata (20%), Cooperia oncophora (4%), Haemonchus contortus (2%) and Bunostomum phlebotomum (1%). The geometric mean EPG was 2.4. Two cows excreted larvae of Dictyocaulus viviparus (0.1 and 0.6 LPG resp.). Worms were found in the abomasa of 108 cows (96%). In all these abomasa Ostertagia spp. was present (100%). Trichostrongylus axei was found in 47 abomasa (43.5%) and two cows (2%) were infected with Capillaria bovis. The geometric mean of the total abomasal worm counts was 1743 and of Ostertagia spp. alone 1615. Almost all male worms were Ostertagia ostertagi, only occasionally Skrjabinagia lyrata10,000) total worm burden. Ostertagia specific antibodies were highest in late summer and autumn and lowest in spring and early summer. The same pattern, although not so pronounced, was observed for the serum pepsinogen values. No clear seasonal pattern was found for the Cooperia specific antibodies. Antibodies against D. viviparus were detected in seven cows (6%).

Evaluation of the persistent efficacy of doramectin and ivermectin injectable against Ostertagia ostertagi and Cooperia oncophora in cattle.

The persistent efficacy of doramectin and ivermectin injectable against moderate and high infection levels of Ostertagia ostertagi and Cooperia oncophora were evaluated in cattle. Calves were allocated to six groups of six animals. On Day 0 animals of Groups I1/I2 and D1/D2 were treated with 0.2mg/kg ivermectin and doramectin injectable, respectively. Animals of the C1, I1 and D1 groups received a daily (moderate) infection of 1000 L3 of O. ostertagi and 1000 L3 of C. oncophora, and animals of the C2, I2 and D2 groups received a daily (high) infection of 10,000 L3 of each species. The animals were infected for 21 days with both species, the infections with C. oncophora and O. ostertagi started from Days 8 and 15 post treatment, respectively. Animals were necropsied on Day 40. The calculation of the persistent activity of ivermectin and doramectin was based on the efficacy against the different developmental and adult stages of both parasites. The present study confirmed that infection levels may influence the duration of persistent efficacy of an anthelmintic. Doramectin had at the moderate infection level a persistent efficacy of at least 35 days against O. ostertagi and at least 28 days against C. oncophora; at the high infection dose persistent efficacy was somewhat shorter i.e. up to 33 days and approximately 28 days, respectively. The duration of persistent efficacy of ivermectin against O. ostertagi at the moderate infection level was between 14 and 25 days, at the high dose level up to 25 days. Persistent efficacy of ivermectin against C. oncophora could, at both infection doses, not be measured, with the present experimental design.

The effect of first season chemoprophylaxis in calves on second season pasture contamination and acquired resistance and resilience to gastrointestinal nematodes.

Two groups of second grazing season cattle, which had been treated with an ivermectin-sustained-release bolus (ISRB) in their first grazing season, were monitored during consecutive years (1995 and 1996) on the same second grazing season pasture. In the preceding year (1994), this pasture had been grazed by yearlings that had not received chemoprophylaxis in their first grazing season. The objectives of the study were, firstly, to investigate whether the chemoprophylactic-treated yearlings were less resistant to gastrointestinal nematodes upon subsequent exposure, and hence excreted more strongyle eggs compared to the control yearlings; secondly, whether an increased susceptibility of the previously treated animals resulted in a yearly increase of the pasture infestation on the second grazing season pasture; and finally, whether this affected the second year weight gain of the animals. In 1996, the yearlings that had been chemoprophylactic-treated in 1995 excreted higher numbers of nematode eggs, compared to the previously 'untreated' yearlings. In addition, the proportion of Cooperia larvae was markedly higher in the faecal cultures from the chemoprophylactic treated-animals, suggesting a negative effect of preventive treatment with an ISRB on the acquired resistance of the animals. However, there was no evidence that the slightly higher egg output in the previously treated yearlings had an effect on the larval contamination of the second grazing season pasture. A significant yearly decrease in the second season average daily weight gains was observed, but it could not be inferred from the results of the parasitological parameters that the differences in second year growth were caused by different levels of resilience between chemoprophylactic-treated and -untreated animals. As the study covered three consecutive second grazing seasons, an effect of differences between years (e.g. in weather conditions or grass growth) on the results cannot be excluded.

Persistence of the efficacy of doramectin against Ostertagia ostertagi and Cooperia oncophora in cattle.

The persistence of the efficacy of doramectin injectable against Ostertagia ostertagi and Cooperia oncophora was evaluated in two studies in calves. In both, the calves were allocated to six groups of six. Calves in the first control group (C1) and first treated group (T1) received a daily infection of 200 L3 of O ostertagi and 200 L3 of C oncophora; the calves in groups C2 and T2 received a daily infection of 1000 L3 of each species, and groups C3 and T3 received 10,000 L3 of each species per day. The calves in the three treated groups each received 0.2 mg/kg doramectin injectable on day 0. In the first study, the calves were infected for 21 days with Cooperia and for 28 days with Ostertagia, and they were slaughtered on day 33. In the second study, the calves were infected for 21 days with both species, the infections with Cooperia and Ostertagia starting from eight and 15 days, respectively, after the treatment, and the animals were slaughtered on day 40. The calculation of the persistence of the activity of doramectin was based on its efficacy against the different developmental and adult stages of the two parasites. The data from both studies indicated that the efficacy of doramectin against Ostertagia persisted for at least five weeks, but no conclusions could be drawn about the effect of the size of the infective doses on the persistence of the activity. In contrast, the Cooperia worm counts from the second study suggested that the efficacy of doramectin against Cooperia persisted for at least four weeks when the calves were exposed to a low or moderate infection level, whereas at the highest infection level it persisted for between three and four weeks.

Gasterophilus intestinalis infections in horses in Belgium.

Over a period of one year, from December 1995 to November 1996, larvae of Gasterophilus intestinalis were found in 193 horse stomachs (58%) of 330 that were examined in two Belgian slaughter houses. When August is excluded, 62% of the stomachs had bot larvae. No other Gasterophilus species were identified. The monthly prevalence ranged from 9% in August to 75% in November and December. The mean intensity of bot larvae varied from 8 in August to 29 in March, and the majority of the horses (67%) harboured less than 50 larvae. Prevalences and intensities were not affected by age, but mares were more frequently infected than stallions and geldings (P < 0.014). The mean size of the lesions increased from 1 cm2 to 17 cm2. The majority of the larvae were localised near the margo plicatus.

Effects of preventive anthelmintic treatment on acquired resistance to gastrointestinal nematodes in naturally infected cattle.

The objective of this study was to investigate the influence of different types of chemoprophylaxis in first season grazing calves on their resistance against a natural reinfection with Ostertagia ostertagi and Cooperia oncophora in the second grazing season. Thirty helminth-naive crossbred calves were randomly divided in three groups of 10 animals. The animals of group B received an ivermectin sustained release bolus on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group ('immune' controls). Although exposure to gastrointestinal nematodes in the first grazing season was only limited, the chemoprophylactic treatments in groups B and D resulted in three distinctly different infection levels (group C > group D > group B). At the start of the second grazing season, six helminth-naive steers (group N, 'susceptible' controls) were turned out together with the second season animals. After 3 weeks of grazing, the 'susceptible' controls were slaughtered, together with four animals from each other group. Parasitological and immunological parameters indicated that resistance to reinfection with Ostertagia was reduced in the chemoprophylactic treated animals, and was negatively related to the degree of suppression of host-parasite contact in the first grazing season (group C > group D > group B > group N). None of the groups had developed a complete resistance against Cooperia yet. A negative relationship was observed between reduction of first grazing season exposure, and weight gains early in the second grazing season. The remaining animals stayed on pasture until the beginning of November. At the end of the second grazing season, levels of acquired resistance against Ostertagia infection were similar in all groups, and all animals had become immune against Cooperia. No effect of first year chemoprophylaxis on total weight gains could be demonstrated. Because of discrepancy between pasture larval counts and tracer worm counts, it was not possible to draw firm conclusions on the effect of chemoprophylaxis on pasture infestation levels in the second year.

Epidemiological observations on gastrointestinal nematode infections in grazing cow-calf pairs in Belgium.

The epidemiology of gastrointestinal helminth infections in beef cows and calves on pasture was studied in Belgium during the 1990 and 1992 grazing seasons. Weight gain, faecal egg counts, generic differentiation of infective larvae, serum pepsinogen levels, herbage larval counts and worm burdens of tracer calves were used as parameters. In Study 1 two groups of ten cows with their spring-born calves grazing on separate pastures (A and B) were monitored during the 1990 grazing season. Ostertagia ostertagi was the predominant species shed by cows and calves. Cows on Pasture A had significantly higher egg counts at turn-out than the B cows, creating a high pasture contamination in the autumn, evidenced by high Ostertagia worm burdens in the Pasture A tracer calves. Calves of both groups showed low egg counts (mean < 60 eggs g-1 faeces, EPG) throughout the grazing season. In Study 2 nine cow-calf pairs were monitored during the 1992 grazing season. The calves were born in winter or spring. Faecal egg counts of the cows remained low throughout the trial period. During the grazing season high egg counts were observed in the calves (mean up to 778 EPG). Cooperia oncophora was the predominant species in the calves. In the cows O. ostertagi, Oesophagostomum, C. oncophora and Trichostrongylus axei were present. It is suggested that, in the first study, the cows were the major source of pasture contamination, while in the second study the winter-born calves, being older and having a higher herbage intake resulting in a higher infection level, were largely responsible for the high Cooperia pasture infection level at housing.

Gastrointestinal nematode infections of first-season grazing calves in Belgium: general patterns and the effect of chemoprophylaxis.

Comparative analyses of the patterns of gastrointestinal nematode infections of first-grazing season cattle in Belgium are presented. The analysis involves 17 studies covering a 10 year period on 13 different farms in Flanders, Belgium. In all studies the calves were divided into an untreated control group, and one or two groups treated with chemoprophylactic systems. Two general infection levels emerged-'sub-clinical' (14 studies) and 'clinical' (three studies). The 'sub-clinical' infections were characterised by no clinical signs of parasitic gastroenteritis in the untreated control groups. Mean faecal egg counts remained low (less than 200), maximum pepsinogen levels only reached about 3500 mU tyrosine, and very small reductions in overall daily weight gain were observed compared with calves given chemoprophylaxis (less than 40 g day-1). Based on these results, on these 'sub-clinical' farms, chemoprophylaxis may not have been needed. In contrast, multiple salvage treatments of the control calf groups were required in the 'clinical' infections. Even with these salvage treatments mean faecal egg counts were high (more than 300), maximum pepsinogen levels were over 5500 mU tyrosine and there was a very large reduction in overall daily weight gain (more than 300 g day-1). However, it was not possible to predict either at turnout, or during the first month afterwards whether an infection on a particular farm would develop into a 'clinical' infestation. With the present data this prediction was possible from 8 weeks (Day 56) onwards, based on faecal egg counts and pasture larval contamination. It was also possible to predict using serum pepsinogen levels on Day 84. Therefore, one possible strategy for the effective control of gastrointestinal nematode infections of calves in temperate regions would be to evaluate faecal egg counts 2 months after turnout, and then only start treatment (i.e. metaphylaxis) if required.