A survey of anthelmintic resistance in nematodes of sheep in The Netherlands

The prevalence of anthelmintic resistance in nematodes of sheep was surveyed in 1994 on 70 farms in the Netherlands. An in vitro egg hatch assay, faecal egg count reduction (FECR) 14 days after treatment, and larval cultures were used as methods of investigation. Oxfendazole was tested on 69, ivermectin on 51, and levamisole on 36 farms. The median effective dose (ED50) of thiabendazole could be determined on 64 farms. On 60 farms (94%) the ED50 value was > or = 0.12 microgram ml-1, which is indicative of the presence of benzimidazole (BZ) resistance. On two farms egg output was too low to do a FECR test. Based on the results of the FECR test, BZ resistance was present on 56 farms (84%), on 2 farms there was a suspicion of resistance and on 9 farms no resistance could be found. No clear indications were found for the presence of resistance against ivermectin or levamisole. BZ resistance was demonstrated in Haemonchus contortus, Cooperia curticei, Ostertagia spp. and/or Trichostrongylus spp. No resistance was observed in species from the genus Nematodirus, Chabertia ovina and/or Oesophagostomum spp.

Anthelmintic resistant nematodes in goats in The Netherlands

A suspected case of anthelmintic resistance on a farm with Angora and Anglo-Nubian goats was confirmed in a controlled test. Twelve lambs of sheep were infected with larvae cultured from faeces of the goats. The lambs were allocated to four groups: untreated controls and lambs treated 21 days after infection with 5 mg kg-1 oxfendazole, 0.2 mg kg-1 ivermectin or 7.5 mg kg-1 levamisole. The lambs were slaughtered 1 week later and post-mortem worm counts were performed. Benzimidazole resistance was found in Haemonchus contortus, Teladorsagia circumcincta, Cooperia curticei and Trichostrongylus colubriformis with the efficacy of oxfendazole being 68%, 31%, 21% and 48% respectively. No resistance was found against levamisole or ivermectin.

[Anthelmintic resistance in sheep nematodes in The Netherlands]

The prevalence of anthelmintic resistant nematodes in sheep was investigated in 1994 with a faecal egg count reduction test (FECRT) and an egg hatch assay (EHA) on 71 farms in the Netherlands. A benzimidazole (oxfendazole) was tested on 70 farms, ivermectin on 51 farms, and levamisole on 35 farms. Based on the FECRT benzimidazole resistance was present on 56 farms, 2 were suspected, on 9 no resistance was observed, while 3 farms could not be tested due to a too low egg output before treatment. No clear indications for resistance to ivermectin and levamisole were found. Benzimidazole resistance was demonstrated in Haemonchus contortus, Cooperia curticei, Ostertagia spp. and/or Trichostrongylus spp. No resistance was seen in species from the genus Nematodirus, Chabertia ovina and/or Oesophagostomum spp. De results of the EHA confirmed the results of the FECRT. On 59 farms the ED50 value was > 0.12 microgram ml-1 thiabendazole.

Ovine lentivirus induced indurative lymphocytic mastitis and its effect on the growth of lambs

The effect of the indurative lymphocytic mastitis caused by infection with maedi-visna virus was quantified by comparing the pre-weaning growth of lambs from infected and uninfected ewes under the same conditions. A total of 73 infected, but clinically healthy, ewes and 75 ewes from a maedi-visna virus-free source were purchased to form a new flock; they were all three years old. The ewes were mated and the flock was managed as a normal field flock. Serum samples were taken at regular intervals and tested for antibodies to maedi-visna virus. The lambs were weighed at birth and at 14, 30, 50 and, finally, 80 days old, when they were weaned. The ewes were slaughtered, their udders were examined histologically, and the lesions were assessed by counting the typical lymphocytic follicles. Sixty-six per cent of the ewes that were seropositive at slaughter appeared to have follicles. A statistically significant association was found between the number of follicles in the udder and the reduction in the growth rate of the lambs. Lambs from ewes with the mean number of follicles weighed 1.7 kg less at weaning.

Prevalence and incidence of scrapie in The Netherlands: a questionnaire survey

Two independent nationwide surveys of randomly selected sheep farmers were conducted: in one a questionnaire was mailed to farmers and in the other the farmers were interviewed. The questionnaire was designed to obtain data on the occurrence of scrapie in the national sheep flock of the Netherlands. Farmers owning 30 or more ewes were selected from a database at the Ministry of Agriculture, Nature Management and Fisheries, resulting in 10,000 addresses. Two lists of names were compiled at random. In the postal survey 700 questionnaires were distributed, and 137 farmers were interviewed directly. The response rate in the postal survey was 37 per cent and in the interview survey 100 per cent. The results from the two surveys did not differ significantly. Six per cent of the farmers indicated that they had at some time observed signs of scrapie in their flock. For the total sheep population in the Netherlands, the prevalence of flocks with sheep showing signs of scrapie was between 3.8 per cent and 8.4 per cent (with 95 per cent certainty). In 1989 and 1990 the incidence rate within infected flocks was 1.27 cases/100 ewes/year, and the incidence rate for the total sample population was 0.1 case/100 ewes/year.

[Serological study of the occurrence of L. hardjo in sheep in The Netherlands]

Sheep (3918) from 137 farms in the regions of North-, West- and Mid-Netherlands and Gelderland were serologically investigated for the presence of antibodies against Leptospira hardjo. Antibodies were detected in 3.3% of the sheep. There were large regional differences with respect to both the percentage of positive sheep and the percentage of positive flocks. All sera from sheep in Gelderland were negative. In West- en Mid-Netherlands there were 0.9 and 6.5% positive sera, respectively, and 19.4 and 32.7% positive flocks. The percentage of positive sheep per positive flocks varied from 1 tot 51.6. Serological positive sheep were from farms with and without cattle. On farms with cattle, there was no clear relationship between serologically sheep and the presence of hardjo antibodies in cattle. It thus seems plausible that sheep can be infected with hardjo independently of cattle.

[Findings in goats at necropsy]

An overview is given of the results of diagnostic investigations into the cause of death of 463 goats performed by the Animal Health Service of West and Middle Netherlands during the period 1 January 1986 to 31 December 1991. The results are discussed and analysed with regard to the age of the animals, the anamnesis, and the abnormalities found at post-mortem examination and with regard to the results of further parasitological, bacteriological, and virological investigations. Enterotoxaemia caused by (epsilon-toxin-positive) Clostridium perfringens was present in 9% of the animals and fibrinous pneumonia with pasteurella in 15% of the animals. Animals with Aujeszky's disease did not show the 'itching' symptom. There were few parasitic infections.

[Early diagnosis of liver fluke infection in sheep]

The sera and livers of slaughtered lambs were studied in October 1987 in order to achieve a suitable interpretation of the indirect haemagglutination assay (IHA) in the diagnosis of fascioliasis in flocks. In view of these studies, it is concluded that the IHA is useful in the early diagnosis of liver fluke infection in lambs. It is recommended to take samples from at least five lambs in each flock. An interpretation model is provided.

Incidence of indurative lymphocytic mastitis in a flock of sheep infected with maedi-visna virus

Sheep in a flock in which 88 per cent of the ewes had antibodies to maedi-visna virus were clinically examined for udder induration during lactation and after drying off. On both occasions about half of the ewes had indurated udders. Histological examination revealed lymphocytic mastitis associated with maedi-visna virus infection, in the udders of six of 25 hoggs (24 per cent), 21 of 39 shearlings (53.8 per cent) and 42 of 67 ewes (62.7 per cent). Distinct lung lesions were found in 8 per cent of the hoggs, 12.5 per cent of the shearlings and 10 per cent of the ewes. The results of a clinical examination of dry udders were correlated with the histological findings.

Environmental contamination by heavy metals and fluoride in the Saeftinge salt marsh (The Netherlands) and its effect on sheep

The Saeftinge salt marsh in the Westerschelde estuary (southwestern part of the Netherlands) represents one of the very few tidal brackish marsh ecosystems in Western Europe. From May 1983 to May 1985 the local pollution of this marsh with metals and fluoride was investigated. Samples from soil and vegetation were analysed monthly for cadmium, lead, copper, zinc, manganese, iron, and fluoride. The amount of these substances in the soil appeared to be related to both the percentage of clay particles and organic matter in the soil and to the frequency of tidal submergences. In vegetation, the pollutants clearly showed a seasonal variation. Adherent clay, deposited on the plants during submergences, contributed considerably to the total amount of these elements. Sheep grazing in the marsh were investigated for renal and faecal excretion of these elements, but no relation between these samples and the seasonal variation in vegetation was found. Presumably sheep consumed vegetation selectively, avoiding the more contaminated plants. Regular clinical inspections of the sheep revealed no signs of acute or chronic intoxication. The organs of sheep that died during the investigation showed increased levels of cadmium in the liver and kidney, and iron in the liver, but not enough to cause alarm. Fluoride found in the rib material, although slightly increased, did not indicate fluorosis. In conclusion, contamination with metals and fluoride, as observed in the salt marsh, apparently does not impair the health of locally grazing sheep. This may be due to selective consumption behaviour of the sheep, their stabling during the winter, limited biological availability of the elements studied, and a sheep management adapted to the local circumstances.

Maedi-visna control in sheep. III: Results and evaluation of a voluntary control program in The Netherlands over a period of four years

The results of the first four years of the Dutch national voluntary maedi-visna control program, which was launched on January 1, 1982, are presented. At the end of the observation period, 1711 breeding flocks representing 70% of the registered breeding flocks participated. The program is based on accreditation of flocks that have passed two successive serological tests with an interval of six months between and post-accreditation tests every 12 months. The flocks have to conform to a set of specific regulations. Sheep sold from such flocks receive a certificate stating that their origin was accredited. A total of 1212 flocks gained accreditation. Of these flocks, 29.5% were free from infection from the beginning, 35.6% were created by total replacement of the original stock, 19.6% employed repeated testing and culling of positives, and 15.3% were created by artificial rearing of colostrum-deprived lambs. A total of 22 flocks lost accreditation due to detection of 36 seropositives. These positives and their progeny were culled, and all flocks regained accreditation after passing the two negative flock tests required. In a total of seven flocks, an unusual course of events during the pre-accreditation stage was observed; this was mainly attributed to late seroconversions and uncommon degrees of horizontal transmission. The results indicate that this certification yields a substantial guarantee of freedom from maedi-visna virus and they indirectly show that the basic design of the program has been adequate.

[Ecthyma, a known disease, of which little is known (author's transl)]

The symptoms of ecthyma are described. Treatment directed against secondary bacterial infection may consist in parenteral or local administration of antibiotics. Experimental inoculation of two commercial vaccines showed that reinoculation will take within 2-3 and five months after the first vaccination. The two vaccines produced a serological response, even after reinoculation. The fact that humoral antibodies are found to be present, is not indicative of the degree of immunity. Inoculation by scarifications will introduce pathogenic virus in a herd without producing a form of immunity, the degree and length of which are known. The virus used on vaccination will spread among the herd.

The efficiency of diamphenethide in controlling natural infestations of Fasciola hepatica in lambs

The activity of diamphenethide against natural infestations of Fasciola hepatica in fattening lambs was assessed on a farm with a noted history of fascioliasis. The main experimental groups, two treated and one control, grazed known contaminated pastures for a twelve week period after which they were removed to fluke-free areas to await slaughter. Three groups of four tracer lambs were each grazed for three successive four week periods with the main flock to determine continuity of infection. A single treatment with diamphenethide at 110 mg/kg bodyweight given when the sheep were removed from the trial area was 96.7% effective against the sub-chronic disease which had developed by this time. Three treatments at 110 mg diamphenethide/kg bodeweight given at intervals of four weeks during the grazing period proved to be 100% effective in preventing the establishment of the disease. Significant benefits in terms of weight gain were exhibited by the treated lambs.

[Tuberculosis among Japanese deer in a deer-park in Goes (author's transl)]

Severe infection with tubercle bacilli of the avian type was detected among Japanese deer in Goes. All animals were disposed of and post-mortem studies were done, which showed that only two specimens were culturally negative. After thorough cleaning and decontamination of fecings and cages and burning of the mown grass during the period from August 1971 to April 1972, the park was repopulated with deer free from tuberculosis. The herd was continued to be free from tuberculosis ever since. Well over one hundred children who occasionally visted the deer-park as well as the attendants of the deer were examined twice (at a four-month interval) using avian tuberculin, the results of the tests being negative.

[Field experinence of the molluscicide "Frescon" in the control of fascioliasis (author's transl)]

The effectiveness of the molluscicide N-tritylmorpholine (Frescon, Shell) in the control of fascioliasis was tested in various field conditions. The effect was not only measured by the study of populations of L. truncatula but its use in prevention was also determined by turning tracer lambs out to grass in treated and control field. The studies showed that Frescon applied at the recommended dose rate is a reliable agent, even in the prevention of acute outbreaks of fascioliasis. The preventive effect was found to be most marked on treatment in the spring (preferable to single treatment during the summer), which is of particular importance in view of the fact that infections may occur in the southern Netherlands during the early grazing season.