The potential for improving welfare standards and productivity in United Kingdom sheep flocks using veterinary flock health plans

Data from industry sources detailing variable costs in 2003 revealed that the average farmer keeping 1000 lowland ewes in the United Kingdom spent 3500 UK pounds annually on veterinary fees and medicines. Despite such expenditure, psoroptic mange and cutaneous myiasis are common in the UK, resistance to one or more anthelmintic group is not only common but increasing in frequency and distribution, and abortion outbreaks caused by Toxoplasma gondii and Chlamydophila abortus are frequently reported by veterinary laboratories. Welfare concerns also arise from farmers' intransigence towards tail docking and castration in lambs (mutilations), reported market forces necessitating long distance road transportation to slaughter plants, and an unwillingness to employ veterinary surgeons for obstetrical problems. The spread of sheep scab in the UK over the past decade illustrates the failure of flock owners to effect rudimentary biosecurity and disease control measures. A first step towards improving the health and welfare of sheep would be the immediate implementation of basic good husbandry practices, including ectoparasiticide treatment for sheep scab eradication, prophylaxis for cutaneous myiasis in selected lambs, and appropriate vaccination strategies for clostridial diseases and certain abortion agents. There would also be money from within current farm expenditure to provide veterinary attention for obstetrical problems affecting up to 2% of ewes per annum. Planned use of ecto- and endoparasiticides is urgently needed to maintain the efficacy of these unique drugs.     

A descriptive study of 'kangaroo gait' in sheep in northern Britain

Two questionnaires were undertaken to obtain improved knowledge of the signalment, incidence and risk factors of the condition termed 'kangaroo gait' (KG; a forelimb locomotor disorder of adult female sheep). The first survey was mailed to 221 veterinary surgeons in practices in northern Britain which provided veterinary care for sheep, and the second was mailed to 438 sheep-flock owners and managers located in the Scottish Borders, who were recruited via their veterinary surgeons. Responses of 84.7 and 30.7% were achieved, respectively. In total, 29.7% of veterinary practices and 24.1% of flock owners and managers had identified one or more cases of KG in their practice area or flocks since the first case was reported in 1976. Almost all respondents indicated that adult females were affected-usually during lactation (and less commonly during late gestation). KG was more common among commercial crossbreeds and less common among sheep grazing hill pasture (than sheep grazing upland or lowland pasture). Cases usually occurred between March and June while sheep were at grass, although it was unclear whether the temporal pattern was associated with grazing or lambing patterns. Stocking densities were significantly higher among affected flocks than among non-affected flocks. The annual number of individuals and flocks identified as being affected had increased since the condition first was identified. Most cases of locomotor disorders resembling KG were not reported to veterinary surgeons.     

Serological cross-sectional survey of psoroptic sheep scab in Switzerland

Sheep scab, caused by the mite Psoroptes ovis, is a notifiable disease in Switzerland. Mandatory prophylactic treatments are carried out in spring for all sheep grazing on common alpine pastures. Despite these strict control measures the number of outbreaks has been increasing in recent years, raising questions on the spread of this epizootic disease. To improve the traditional microscopic diagnosis, we developed an ELISA for the specific determination of antibodies against psoroptic antigens with sensitivity and specificity of 93.7 and 96.5%, respectively. Using this test, a serum bank, representative of the sheep population in Switzerland (approximately 15% of registered sheep flocks, randomly chosen, collected between February and May 1998), was screened. The prevalence using 16,404 sera was 10.4, and 11.9% of the 2083 flocks were diagnosed as positive. Additionally, there was a significant increase found for mean seropositivity relative to the flock size (P<0.001, linear regression). Therefore, larger flocks had a higher risk of sheep scab, which may be caused by more frequent animal movement. Spatial analysis of the results revealed a region with significantly higher risk (relative risk = 3.5, P<0.001) of seropositivity, where no cases have officially been notified in the period between 1997 and 1999. The next goal is to establish an efficient control strategy based on serological monitoring of the total sheep population.     

Salmonella Brandenburg: case-control survey in sheep in New Zealand

AIM: To identify environmental, management and animal risk factors associated with the occurrence and severity of disease attributed to Salmonella Brandenburg infection in sheep. METHODS: A retrospective case-control study was undertaken, and details of disease prevalence and farm management methods were collected from two affected regions in southern New Zealand. Associations between possible risk factors and disease attributed to S. Brandenburg were evaluated using odds ratios. A case-control approach was used to assess risk factors associated with outbreaks of disease at the farm level, using unaffected farms as controls. A separate analysis was then performed within affected farms only, to assess risk factors associated with increasing severity of disease. RESULTS: Data were collected from 405 farms containing a total of 1,170,737 ewes. Of the 177 case farms, 172 (97%) had diseased mixed-age ewes, 78 (45%) had diseased two-tooth ewes and eight (5%) had diseased hoggets. Increased odds of farms being affected with S. Brandenburg were reported for farms that strip-grazed sheep, and as total numbers of sheep increased. Reduced odds of being affected were associated with feeding crops, and hilly terrain on those farms not feeding crops. Within affected farms, increased severity of disease was associated with strip-grazing and feeding hay in TT flocks, and later removal of rams in MA flocks. Reduced severity of disease was associated with shearing or crutching after July, and vaccination of sheep against Salmonella spp. CONCLUSIONS: Salmonella Brandenburg occurred in flocks that reported using intensive farming methods and that maintained high numbers of sheep. CLINICAL RELEVANCE: Risk factors associated with the occurrence and severity of the disease due to S. Brandenburg have been identified. This information is necessary to identify preventative and control measures that may be effective in reducing the risk of disease.     

Control and management of sheep mange and pediculosis in Great Britain

The patterns of insecticide use for the prevention and control of sheep lice and Psoroptes mites, in England, Wales and Scotland, in 2003-2004, were examined using data from a retrospective questionnaire. Overall, 375 of the 966 (39%) farmers who responded said that they treated at least once to prevent louse infestation. For scab, 426 of the 966 (44%) farmers who responded said that they had treated prophylactically to prevent the disease. There were no significant differences between regions in the number of times farmers treated to prevent lice (chi(2)=0.54, P>0.1) or scab (chi(2)=0.16, P>0.1). Among the farmers who applied prophylactic treatment 23% had a subsequent outbreak of lice and 17% had an outbreak of scab. The majority of sheep farmers who used preventative treatment did so in June and July. Where a second treatment was given it was largely in October. For lice, 52% of farmers used pyrethroids to prevent and 70% to treat louse infestation. For scab prophylaxis, most farmers said that they used either the macrocyclic lactones (41%) or organophosphates (36%) as a preventative. For the therapeutic treatment of scab outbreaks, macrocyclic lactones (largely doramectin) were used on 58% of sheep farms. The high national prevalence of sheep scab and pediculosis indicates that current control methods are failing to contain these ectoparasites. The results of this study suggest that a large proportion of insecticide applications take place at times of year when they might expect to be relatively ineffective, and the use of inappropriate compounds for the parasites in question is common. The widespread use of macrocyclic lactones in particular for scab prevention and control is of concern, because of the additional use of these compounds in parasitic worm control and the potential that their overuse will hasten the development of resistance.     

Effect of agro-ecological zone and grazing system on incidence of East Coast Fever in calves in Mbale and Sironko Districts of Eastern Uganda

Between May 2002 and February 2003 a longitudinal survey was carried out in Mbale and Sironko Districts of Eastern Uganda to determine the influence of agro-ecological zones (AEZ) and grazing systems on tick infestation patterns and incidence of East Coast Fever (ECF) in bovine calves. The study area was stratified into AEZ (lowland, midland and upland) and grazing systems {zero grazing (ZG), restricted-outdoor grazing (ROG) and communal grazing (CG)}, whose strata had previously been shown to influence the prevalence of ECF, babesiosis and anaplasmosis. One hundred and eighty-five smallholder dairy farms with a total of 198 calves of both sexes, between the ages of 1 day and 6 weeks, were purposively selected from the AEZ–grazing system strata. Nine dynamic cohorts (11–51 calves in each) of these calves were examined and sampled monthly. Ticks infesting the calves were counted from one side of the animal body and categorized into the different species, sex and feeding status. Sera were collected at recruitment and monthly thereafter and antibodies against Theileria parva, T. mutans, Babesia bigemina, B. bovis and Anaplasma marginale were measured using ELISA. Tick challenge (total and specific) varied with AEZ and grazing system. The risk of infection with T. parva was higher in the lowland zone compared to the upland zone (hazard ratio (HR) = 2.59; 95% CI: 1.00–6.34). The risk of infection with T. parva was higher in the CG system than the ZG system (HR = 10.00; 95% CI: 3.61–27.92). The incidence risk for sero-conversion, over the 10 months study period, was 62, 16 and 9% in the lowland, midland and upland zones, respectively. Ninety-eight percent of the calves in lowland-CG stratum sero-converted by the age of 6 months, while 56 and 8% did so in the lowland-ROG and the lowland-ZG stratum, respectively. The results of this study show the need to consider farm circumstances and the variation in ECF risk, both spatially and temporally when designing control strategies for ECF.     

The immunogenic properties of Salmonella typhi-murium in sheep

Extract

Salmonellosis of adult sheep due to infection with Salmonella typhi-murium was first recognized and confirmed bacteriologically in New Zealand in March, 1949. Since then, 100 outbreaks have been identified, most of which have occurred in the North Island. These outbreaks have occurred on farms varying in topography and under different conditions of management. With one exception, none of these outbreaks, which occur mainly in late Summer and Autumn, has been associated with transit by truck or rail journeys. In 1950, consideration was given to the possibility of affording protection by prophylactic vaccination, and the purpose of this paper is to record the results of some experiments carried out at Wallaceville and in the field with that object.     

Parainfluenza 3 vaccination of sheep

Outbreaks of pneumonia associated with Pasteurella haemolytica have occurred in sheep in the area of Perthshire served by this practice, and on some farms the disease has been an important annual cause of loss. Serological evidence was obtained that parainfluenza 3 (PI3) virus might be implicated as a predisposing factor to pasteurellosis. A live attenuated PI3 virus vaccine licensed for use in cattle was given intranasally to ewes on one farm. Many sheep seroconverted and outbreaks of pneumonia were negligible around the subsequent lambing time. The protection of the flock appeared to last for one season only. Subsequently ewes and lambs on other farms were vaccinated and on these farms there were fewer deaths than expected due to pasteurellosis.     

The use of moxidectin for the prevention and treatment of psoroptic mange (scab) in sheep.

The introduction of systemic injectable products, belonging to the avermectin/milbemycin class of antiparasitic compounds, has provided an alternative to dips for sheep scab control. Their main advantages are that they are quicker and safer to use, cause less stress to the sheep (hence can be used in heavily pregnant ewes), do not require any special handling facilities for their use and do not present the same environmental concerns over disposal of spent product. Moxidectin, a second generation milbemycin, has recently been registered as an injectable product for the prevention and treatment of sheep scab. Laboratory and field studies carried out in the UK and Ireland have shown that two injections at a dose rate of 200 mg/kg bwt., 10 days apart, are 100% effective in the treatment of scab. Further studies have shown that a single injection at the same dose rate will protect against infestation or reinfestation for a period of at least 28 days. This long persistent activity has been evaluated in two large-scale field prophylactic trials, one in Ireland and one in the UK, involving over 16,000 sheep, in which it was demonstrated that a single injection of moxidectin is a safe and effective alternative to dips for routine prevention of scab.     

Lythrum hyssopifolia (lesser loosestrife) poisoning of sheep in Victoria

Objective To document an ovine disease attributed to the consumption of Lythrum hyssopifolia (lesser loosestrife). Procedures Historical and histological review of field and experimental cases. Results 1–20% mortality occurred in sheep flocks grazing paddocks where L. hyssopifolia was the predominant green vegetation. Well‐documented disease outbreaks occurred in summer on nine farms across Victoria between 1974 and 2002. Liver damage occurred in all nine outbreaks, with kidney damage in at least eight. Hepatocyte necrosis was usually zonal to midzonal (zone 2) in the liver samples from four farms and periacinar (zone 3) in those from three farms, but some livers showed only single‐cell necrosis. Multinucleate hepatocytes near necrotic areas were a feature in six cases. Proximal tubular epithelium appeared to be the primary renal target and brown granules were often present in renal tubules. Biochemical and histological evidence of liver and kidney damage was obtained from two sheep experimentally pen‐fed harvested L. hyssopifolia. Conclusion Chemicals in L. hyssopifolia are toxic to ovine hepatocytes and renal tubular epithelial cells.     

Farmers'' opinions on welfare, health and production practices in extensive hill sheep flocks in Great Britain

Despite large numbers of hill sheep reared in the UK, little is known about how hill farmers react to health challenges in their flocks. This paper addresses this lack of knowledge of sheep health management practices and presents farmers' opinions and concerns, particularly regarding ectoparasite control. Focus groups and interviews with UK hill sheep farmers were carried out to collect information on management practices, health concerns, in addition to incidence and impacts of six major ectoparasites (ticks, lice, sheep scab mite, blowfly, keds and headfly), to determine how they viewed the effects of ectoparasites and their control on production practices.

We conclude that despite variations between hill sheep farm conditions and levels of input, similar health concerns and ectoparasite issues were found across different hill sheep farming areas of the UK. Farm labour was also an important issue and most farmers would prefer more labour to be available to effectively manage ectoparasites in their flocks. Finally, there was variation in farmers' opinions of the impact of ectoparasite species on welfare and productivity. This variation in opinion can be related to a trend in their past experience of ectoparasites, but no relationships were found with the animal health treatments farmers use, the number of animals in their flock or variation in the type of grazing land available.     

Within-flock transmission of sheep scab in naive sheep housed with single infested sheep.

The within flock transmission of sheep scab was studied in two trials, which lasted 14 and 12 weeks, respectively. A total of 40 non-infested, scab-naive sheep were divided into six groups of between 6 and 20 individuals. Each group was subsequently housed with a single infested index case, carrying scab lesions of different ages. The groups of sheep in both trials were video recorded continuously and all the sheep were individually examined on a weekly basis. The occurrence of transmission was measured in two ways: first, by the detection of early scab lesions during clinical examination and, second, by an increase in the rubbing of individual sheep as noted from the analysis of the video recordings. These two methods complemented each other in predicting the week on which transmission occurred. Overall, transmission was detected in 34 of the 40 scab-naive sheep. Transmission was shown to occur at about the time when the population of adult mites in lesions on index cases reached their peak numbers. The highest number of mites at this time, however, differed markedly between index sheep. There was no obvious relationship between the incidence of transmission and the time index sheep spent rubbing each day or other index sheep variables, including the age of the lesion or the time since the introduction to the scab free sheep.     

Avermectin-resistance in gastrointestinal nematodes of Boer goats and Dorper sheep in Switzerland

Anthelmintic resistance in gastrointestinal nematodes among small ruminants is widespread in South Africa and Dorper sheep and Boer goats have been imported into Switzerland from this country on a number of occasions. Therefore, this study aimed to investigate the occurrence of avermectin (AVM) resistant gastrointestinal nematodes (GIN) in these breeds in Switzerland. A total of 24 Boer goat farms and 12 Dorper sheep farms participated in the study. According to the faecal egg count reduction test (FECRT) AVM-resistant GIN populations were confirmed in 7 of the 24 Boer goat farms and suspected in a further 8 farms. Likewise AVM-resistance was confirmed in 2 of 12 Dorper sheep farms and suspected in a further 6 farms. Haemonchus contortus and Trichostrongylus spp. were the dominant resistant species according to larval cultures. In the farms with detected AVM-resistance the animals were additionally treated with levamisole after natural reinfection. With the exception of one farm with a 'close-to cutoff-result' the FECRT gave no indication for resistance against levamisole. The results indicate that AVM-resistance is widespread in Swiss small ruminant farms keeping Boer goats and Dorper sheep. The common tradition of grazing animals from different farms on prealpine and alpine pastures could favour the spread of resistant populations within the country.     

Salmonella in sheep in Iceland

In 1995 several outbreaks of food poisoning in humans occurred in Iceland, that were traced to salmonella contamination of singed sheep heads. This prompted us to study the prevalence of salmonella infection in sheep and to trace where and how infection might have occurred. Faecal, intestinal contents and tonsillar samples were collected in the spring and autumn from sheep on 50 farms in the southwestern part of the country, where salmonellosis had been detected and from 5 farms in the northwestern part of the country. All faecal samples from the southwest were negative, whereas samples from 3 farms obtained in the autumn in the northwest were positive. Tonsillae taken in the autumn were positive in sheep from 3 farms in the southwest and 2 in the northwest. Our results show that salmonella infection is rare in Icelandic sheep but healthy carriers my harbour the bacteria in tonsillae. Salmonella was not detected in drainage from slaughterhouses nor in singed sheep heads.     

Concentration of conjugated linoleic acid in grazing sheep and goat milk fat

The conjugated linoleic acid (CLA) content of grazing sheep and goat milk fat, throughout their lactation period, was examined. Six sheep and six goat representative farms were selected at random and milk samples were taken at monthly intervals for fatty acids profile determination. Sheep and goat nutrition was based on natural grazing and on supplementary feeding during the winter months. From April onwards, grazing native pastures was the only source of feed for sheep and goats. The University farm whose sheep are kept indoors all year round without any grazing, was also used as reference. Fifteen individual milk samples were also taken in April from a sheep and goat farm respectively, in order to see the variability of CLA inside the farm. The results showed that: a. the CLA content of grazing sheep and goat milk fat increased significantly in April–May (early growth stage of grass) and then declined while that of indoors kept sheep was more or less constant during the same period, b. the isomers cis-9, trans-11 and trans-10, cis-12 of CLA were found in grazing sheep milk fat, while in indoors kept sheep and goats' milk fat only the cis-9, trans-11 isomer was found, c. the CLA content of sheep milk fat was much higher than that of goats, d. a negative correlation between sheep milk fat and CLA content was found and e. there was considerable variation in milk fat CLA content between sheep and goat farms and inside the farms.     

Approaches to vaccines for Psoroptes ovis (sheep scab)

A brief outline of the history of sheep scab in the UK is presented together with the current chemical methods used for its control and problems associated with these. Possible alternative approaches to control are discussed, as are selected aspects of the physiology of Psoroptes ovis and the pathogenesis of the scab lesion from the perspective of control through immunisation. Evidence is provided that immunity to the disease can indeed be acquired, both naturally after a previous infection and following inoculation of mite proteins in adjuvant. These results support the view that control by vaccination may be possible, although little is known to date about the antigens involved or the mechanism of protection.     

The behaviour of sheep with sheep scab, Psoroptes ovis infestation.

Methods of behavioural data collection as applied to the study of sheep scab are described. The behaviour of a number of marked animals within an affected flock was recorded using an event recorder. Focal sampled data were analysed for duration and frequency of the observed behaviours. In addition, the flock was observed at intervals and the instantaneous behaviour of each animal recorded. These data were compared with similar observational data from the same flock recorded at intervals during post-treatment recovery. Sheep scab resulted in pathological behaviours of rubbing, scratching and biting at the lesion, and these resulted in interruption of the normal behaviours, grazing, cudding and idling, but did not result in reduced levels of these behaviours. Infested sheep showed stereotypic mouthing behaviour, initiated by rubbing or scratching, or in some cases without any external stimulus. No stereotypic behaviour was seen in animals after treatment. The implications of the behavioural data for the welfare of the sheep is discussed.     

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

AIM: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand. METHODS: An interview-based cross-sectional study of grazing management and anthelmintic usage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand. RESULTS: Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target sample size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased. CONCLUSIONS: Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.     

A spatial risk assessment of bighorn sheep extirpation by grazing domestic sheep on public lands

Bighorn sheep currently occupy just 30% of their historic distribution, and persist in populations less than 5% as abundant overall as their early 19th century counterparts. Present-day recovery of bighorn sheep populations is in large part limited by periodic outbreaks of respiratory disease, which can be transmitted to bighorn sheep via contact with domestic sheep grazing in their vicinity. In order to assess the viability of bighorn sheep populations on the Payette National Forest (PNF) under several alternative proposals for domestic sheep grazing, we developed a series of interlinked models. Using telemetry and habitat data, we characterized herd home ranges and foray movements of bighorn sheep from their home ranges. Combining foray model movement estimates with known domestic sheep grazing areas (allotments), a Risk of Contact Model estimated bighorn sheep contact rates with domestic sheep allotments. Finally, we used demographic and epidemiologic data to construct population and disease transmission models (Disease Model), which we used to estimate bighorn sheep persistence under each alternative grazing scenario. Depending on the probability of disease transmission following interspecies contact, extirpation probabilities for the seven bighorn sheep herds examined here ranged from 20% to 100%. The Disease Model allowed us to assess the probabilities that varied domestic sheep management scenarios would support persistent populations of free-ranging bighorn sheep.     

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

AIM: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand.

METHODS: An interview-based cross-sectional study of grazing management and anthelmintic useage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand.

RESULTS: Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target sample size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased.

CONCLUSIONS: Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.