D J Wilson

Unexpected production loss caused by helminth parasites in weaned beef calves.

SHEEP farmers are generally quick to consider helminth parasitism as the cause of diarrhoea and illthrift in their lambs, because they are aware that effective helminth control using anthelmintic drugs is difficult to achieve. There is a general awareness among sheep farmers of the production-

Teladorsagia circumcincta resistance to moxidectin and multiple anthelmintic groups in ewes following use of the persistent drug before lambing

This paper describes the nematode control strategy adopted by a Scottish hill sheep farmer. It provides an example of the limited use of anthelmintic drugs, targeted towards control of the periparturient rise in faecal nematode egg output in ewes and exploitation of grazing management, resulting in limited exposure of naive sheep to infective larvae on pasture. Resistance to benzimidazole, imidazothiazole and macrocyclic lactone anthelmintics, and to a combination of a macrocyclic lactone and imidazothiazole anthelmintic drugs was diagnosed. The targeted use of a persistent anthelmintic drug to control a periparturient rise in faecal nematode egg output in ewes may be unnecessary and selects strongly for resistance when the reservoir of anthelmintic-susceptible nematodes in refugia is small at the time of treatment. However, the use of a persistent anthelmintic drug in a selective proportion of ewes can be important and probably does not select strongly for resistance when the reservoir of anthelmintic-susceptible nematodes in refugia is large at the time of treatment. The former circumstances might arise on many Scottish hill sheep farms, whereas the latter may occur on upland and lowground farms, depending on previous grazing management, anthelmintic use and winter weather conditions. These factors must be taken into account when preparing sustainable health plans for nematode parasite control in individual sheep flocks.

Relative inefficacy of pour-on macrocyclic lactone anthelmintic treatments against Cooperia species in Highland calves

Resistance to macrocyclic lactone anthelmintic drugs currently threatens the sustainability of economic sheep farming in the UK. Until recently, macrocyclic lactone resistance in cattle nematode parasites has been considered to present a much lesser threat, and most UK cattle farmers have not

Observations on the epidemiology of autumn nematodirosis in weaned lambs in a Scottish sheep flock

Nematodirosis was diagnosed in the south-east of Scotland during two consecutive autumns in lambs which were grazed on the same field. The problem was unpredicted based on the knowledge of the pasture and animal management, and rudimentary understanding of the behaviour of free-living stages of Nematodirus battus in the region. Unlike the epidemiology that has been described in the south of England, whereby autumn infection of lambs is believed to arise from autumn hatching of eggs shed during the previous spring without prior chilling, it is concluded that the autumn nematodirosis in a particular sheep flock in Scotland most likely arose following prolonged survival of larvae hatched during the spring from eggs shed during the previous summer, following periods of cold exposure over the previous winter. The infective larvae survived in large numbers in a small, sheltered strip of rough grazing, where they would have been protected from harmful ultraviolet radiation and heavy rainfall, before infecting lambs during the autumn. Understanding of the evolutionary potential, nematode parasites to adapt to changing environmental conditions depends on a thorough clinical investigative approach, and is a prerequisite for future preventive management.

Use of a long acting injectable formulation of moxidectin to control the periparturient rise in faecal Teladorsagia circumcincta egg output of ewes

A field study was conducted in a sheep flock in the south east of Scotland with a history of ivermectin resistance in Teladorsagia circumcincta. The objective of the study was to compare the effects of single anthelmintic treatments in ewes before turn-out onto pasture that was contaminated with a moderate level of overwintered, ivermectin resistant, T. circumcincta infective larvae. The ewes were treated according to label directions with either a long acting injectable formulation of moxidectin (1mg/kg; affording up to 14 weeks persistent action against macrocyclic lactone (ML)-susceptible T. circumcincta) or an oral formulation of moxidectin (0.2mg/kg; affording up to 5 weeks persistent action against ML-susceptible T. circumcincta). The lambs were enrolled in the normal management of the farm, and received a total of three oral ivermectin treatments during the 16 week study. The efficacy of both treatment strategies in controlling the periparturient rise in faecal nematode worm egg counts and subsequent pasture contamination was assessed from the faecal worm egg counts of the ewes and their lambs between lambing and weaning. Ewes that were treated with the oral formulation of moxidectin shed approximately 3.5 times more T. circumcincta eggs between lambing and weaning than ewes that were treated with the long acting formulation of moxidectin. This difference was reflected in the faecal worm egg counts of the lambs that were grazed alongside the different treatment groups of ewes. The results of the current study demonstrate persistent efficacy of the long acting formulation of moxidectin against an ivermectin resistant T. circumcincta population. The decreased pasture contamination after treatment could lead to improved lamb growth and a need for fewer anthelmintic treatments, thus potentially reducing one possible selection pressure for anthelmintic resistance. However, treatment with the long acting formulation of moxidectin would give rise to fewer susceptible nematodes being present in refugia, which could increase another possible selection pressure for anthelmintic resistance, depending on the subsequent grazing management of that pasture. The rationale for use of a persistent anthelmintic drug to control the periparturient rise in faecal ML-resistant T. circumcincta egg output of the ewes is discussed and potential differences in selection for macrocyclic lactone anthelmintic resistance using the different formulations of moxidectin are acknowledged.

Identification of Sarcocystis capracanis in cerebrospinal fluid from sheep with neurological disease

Protozoal merozoites were identified in the cerebrospinal fluid of two sheep with neurological disease in the UK. Polymerase chain reaction (PCR) identified the merozoites as Sarcocystis capracanis, a common protozoal pathogen of goats. This is the first report of this species infecting sheep and may represent an aberrant infection with sheep acting as dead end hosts, or alternatively could indicate that sheep are able to act as intermediate hosts for S. capracanis, widening the previously reported host range of this pathogen. It is possible that S. capracanis is a previously unrecognised cause of ovine protozoal meningoencephalitis (OPM) in the UK.

Hepatic encephalopathy associated with cobalt deficiency and white liver disease in lambs

The application of the larvae required no sedation and avoided the potential side effects of repeatedly sedating an elderly, hospitalised donkey at risk from conditions such as impactive colic, choke, cardiac disease or hyperlipaemia. Distracting it with food was sufficient to allow the larvae to be applied in a controlled way. The wound required attention only every five days, rather than daily, resulting in a further reduction in stress. As a result of the reduction in wound pain and the cessation of injections of drugs, the donkey showed fewer signs of stress, and became relaxed and comfortable in the presence of a veterinary surgeon. As stress in donkeys can contribute to delays in wound healing and predispose them to the onset of life-threatening conditions such as hyperlipaemia, this benefit should not be understated. The disadvantages of the treatment were considered of minor significance. Of the eight batches of maggots received in the post, one batch were dead on arrival and another batch failed to become established in the wound. There were two potential reasons for this failure. First, there was probably a delay of more than 24 hours between the despatch of the larvae and their application to the wound. Secondly, the area around the wound margins had been cleaned with dilute chlorhexidine (Hibitane; Schering-Plough Animal Health) which could have had an adverse effect on the establishment of the larvae if some run-off into the wound had occurred. An unforeseen disadvantage was the noise and sight of the feeding larvae, which was repulsive to some members of the hospital staffwho were not enthusiastic about being involved with the day to day care of the donkey. The treatment with larvae was a safe and effective method for treating a severe, focal, suppurative panniculitis in an aged donkey. The method had several advantages over conventional medical and surgical treatments.