Epidemiology of trichostrongylidosis in cattle: development of infective larvae in the second part of the grazing period and their contribution to infections in the same year

Failure of Duddingtonia flagrans to reduce gastrointestinal nematode infections in dairy ewes

A field study was conducted on three Swiss farms to investigate the efficacy of Duddingtonia flagrans against naturally acquired infections of gastrointestinal nematodes in adult dairy sheep. On each farm the ewes were divided into two equal groups. One group received Duddingtonia during a period of 4 months at a daily dose rate of 10(6) chlamydospores per kilogram body weight, the second group acted as controls. At an overall moderate infection level in all farms D. flagrans did not have a significant effect on the observed parasitological parameters with the exception of a significantly reduced herbage infectivity in one farm. In contrast, the results from faecal cultures indicated a mean suppression of larval development during the fungus-feeding period between 82, 89 and 93% on the three farms, respectively. The discrepancy observed between the fungus efficacy in coprocultures and on pasture, which was also observed in several other studies deserves further research.

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.

Parasite control in transhumant situations

Transhumance is defined as 'seasonal moving of livestock to regions of different climate'. It is an integral part of livestock production in many parts of the world and takes several forms including moving of livestock from lowland to mountainous pastures or from dry to humid areas. The impact of transhumance on parasite populations of livestock and on parasite control is described, mainly using examples from Europe. The epidemiology of trichostrongylidosis of cattle, mainly caused by Ostertagia ostertagi and Cooperia oncophora, is characterised by prolonged survival of overwintered infective larvae until the end of June. Cattle moved to such contaminated pastures in a transhumant grazing system are exposed to these larvae and may be protected, during the second half of the grazing season until autumn, by a late application (June/July) of an intraruminal drug-release device. Community pastures used in a transhumant system with mixed grazing of young cattle originating from various farms may enhance transmission of dictyocaulosis. Therefore, specific prophylactic measures are required. Hill sheep nematode populations may differ from those in lowland sheep in that Haemonchus contortus generally plays a minor role in hill sheep in which Ostertagia circumcincta and Nematodirus spp. predominate. Infections with Fasciola hepatica and Dicrocoelium dendriticum can be acquired on mountainous pastures by cattle, sheep and other livestock grazing in a transhumant system as intermediate hosts of these parasites may find suitable habitats in these regions. There is evidence that in the prealpine and alpine area both parasites are mainly transmitted in two-season cycles. Further examples for the impact of transhumance on parasite-host inter-relationships include cysticercosis in cattle, echinococcosis, psoroptic manage in sheep, tick-borne fever of cattle, and hypodermosis in cattle. These are described and discussed.

Prophylaxis of bovine trichostrongylidosis in the alpine region: effect of pasture contamination on infections in calves receiving a morantel sustained-release trilaminate bolus in mid-July

In the alpine region, mixed grazing systems with cattle of different age, origin and prophylaxis against trichostrongylid infections are most common. Under these conditions the administration of anthelmintic devices to susceptible calves is frequently postponed to June or July to achieve a better protection during the period of increased pasture infectivity in summer and autumn. In a field experiment with 27 first-year grazing calves a morantel sustained-release trilaminate bolus (MSRT, Pfizer) was given to two groups (Groups A and B) of nine naturally infected calves each, on 22 July. Calves of Group B were moved to a clean pasture (B) 1 day later, whereas the calves of Group A remained on the previous pasture (A) together with nine untreated calves (Group C). The contamination with infective larvae (L3) on Pasture A remained below 1000 L3 kg-1 dry matter, which was sufficient to produce clinical parasitic gastroenteritis in five of nine control calves. The MSRT bolus reduced the mean egg output by more than 90% within 14 days after administration and prevented clinical parasitic gastroenteritis in the calves of Groups A and B. Owing to the persisting infection risk on Pasture A, the mean serum pepsinogen levels reached about 3000 mU tyrosine in the calves of Group A in September compared with approximately 2000 mU in Group B grazing the clean pasture. However, the differences in pasture contamination were not reflected in the mean bodyweight of the calves, which were 20 kg heavier at the end of the trial in both MSRT-treated groups compared with the control calves (P < 0.01). As there is a high probability that a moderate larval contamination is present on prealpine and alpine community pastures in summer, the metaphylactic use of an MSRT bolus in mid-July is likely to limit trichostrongylid infections within a subclinical range and thus provides sufficient protection of susceptible calves against parasitic gastroenteritis.