Veterinary Services

Since 1995 SAC C VS has confirmed between 35 and 72 outbreaks of sheep scab each year (Figure 3 - see top right-hand side).  Since 2006 the number has stabilised between 40 and 52 per year as veterinary surgeons have become more confident in diagnosing sheep scab on clinical examination only.  In contrast, the number of outbreaks of lice has increased over the past 10 years.  The Scottish Government introduced the Sheep Scab Order (2010) last December.  This did not result in an increase in the number of laboratory diagnoses of sheep scab with 32 diagnoses obtained in the period January to September in 2010 and 2011.  SAC C VS continues to offer free sheep ectoparasite examinations to veterinary surgeons in practice who wish independent laboratory confirmation of their presumptive diagnosis.  Although sheep scab is considered as a disease seen in the winter and spring, in 2010 and 2011 sheep scab was confirmed by SAC C VS throughout the year whereas lice was only recorded it the winter and spring (Figure 4  - see top right-hand side).

Toxic conditions

 
Perth diagnosed chronic copper poisoning in a Beltex tup from a group of seven being prepared for sale. Two other animals in the group had died recently. The group was grazed in a small paddock and fed a commercially produced coarse mix.  Necropsy revealed generalised jaundice with an orange liver and black kidneys.  Assay of liver and kidney tissues showed copper levels of 44,100 umol/kg DM (314-7,850 umol/kg DM) and 11,660 umol/kg DM (</= 787 umol/kg DM) respectively.  Analysis of the coarse mix found its copper content to be 9.46 mg/kg DM which is considered safe for a sheep feed. SAC C VS recognises that chronic copper poisoning will occur in sheep fed diets with an acceptable copper content.  In these cases factors such as breed predisposition, chronicity of feeding, other forms of supplementation and/or concurrent grazing of pastures low in molybdenum / iron / sulphur can be significant.

Inverness diagnosed suspected salicylanilide poisoning in a four-month-old lamb. The farmer reported that two to three lambs became blind each year and did not recover.  The clinical signs in the lamb comprised blindness with no visible eye lesions.  Characteristic head shaking was noticed with the head being moved slowly to the right, followed by a quick left movement back to mid-line.  The animal was afebrile and displayed a high stepping gait and occasional circling. Histopathological examination of the brain revealed changes consistent with a diagnosis of a toxic encephalopathy such as those reported in cases of salicylanilide poisoning e.g. closantel or rafoxanide.  Blindness was first noticed in July one month after the lambs had been treated with a product containing closantel.  At the time of submission the lamb weighed 18kg however the dose of closantel administered more than two months earlier was adequate for a 25kg lamb.  Blindness in lambs due to inadvertent closantel overdose has been reported previously, (Barlow and other, Veterinary Record, 2002, 151, 25-26).

Parasitic diseases

A high count of 7,975 strongyle eggs per gram was identified by Aberdeen in a pooled dung sample from a group of five-month-old Suffolk cross and Texel cross lambs some of which were  scouring. The lambs were wormed four weeks prior to and at the time of faecal sampling with a benzimidazole wormer. SAC CVS advised carrying out a post-dosing efficacy check. Samples received 14 days post dosing revealed 1050 strongyle epg indicating treatment failure, one explanation for which could be anthelmintic resistance.

The first outbreaks of acute fasciolosis were diagnosed in Ayrshire flocks. In one outbreak eight Scottish blackface ewes were found dead. The group had received a fluke and worm dose in June and had not received a booster clostridial vaccination. Postmortem examination revealed hepatic haemorrhage and necrosis, and immature Fasciola hepatica liver flukes 2-3mm in length were recovered from lesions. Black disease was also confirmed by FAT examination and histopathology.  Immediate fasciolicide treatment and clostridial vaccination were recommended. 
In another outbreak eight mule ewes died acutely having been treated with triclabendazole in mid May and again four days prior to death. Haemorrhagic tracts were evident on the surface and throughout the liver parenchyma, with areas of fibrosis. Large numbers of immature liver flukes 2-20 mm in length were recovered from lesions. Triclabendazole inefficacy was suspected and the attending veterinary surgeon was advised to inform the Veterinary Medicines Directorate.

Generalised and systemic conditions

Systemic pasteurellosis due to Mannheimia (Pasteurella) haemolytica was diagnosed in an Ayrshire flock causing deaths in five-month-old lambs. Splenomegaly and the additional recovery of Staphylococcus aureus from the viscera suggested that tick-borne fever may have predisposed the animals to systemic infection. Further investigation was initiated to follow up this possibility.

Cellulitis and abscessation associated with an injection site reaction were diagnosed by Dumfries as the cause of death of two recently purchased lambs. Subcutaneous oedema was found over the right neck and forequarter in each case accompanied by a focal area of deep seated infection from which Actinomyces pyogenes and Fusobacterium necrophorum were isolated. The history indicated that the lambs were vaccinated after purchase and this was considered to be the likely source of the lesions seen.  Examination of a third lamb two weeks later revealed a subcutaneous abscess approximately 7cm in diameter in the right neck. Micro-abscesses were scattered throughout the right lung and septic arthritis affected multiple joints (Figure 5  - see top right-hand side). These findings supported the previous diagnosis of infection at the injection site and indicated a secondary bacteraemia.  Actinomyces pyogenes, Bacteroides sp. and Fusobacterium sp. were isolated from the abscess and the joints.  Losses continue, but eight of the 100 lambs died and several others were lame.  The group was sourced from three flocks and mixed together before vaccination.  All the affected lambs were from the same flock. SAC C VS have no clear explanation for this.

Alimentary tract disorders

Dumfries diagnosed Johnes disease in four sheep from three farms.  Three to four-year-old mule and blackface ewes were affected with a history of weight loss since weaning.  The blackface ewes were purchased as ewe lambs.  One case had submandibular oedema while a second had ascites indicating hypoproteinaemia.  Varying degrees of thickening and corrugation of the intestinal mucosa was seen and yellow pigmentation was present in all cases.  Both ZN smears for acid fast organisms and ELISA testing proved positive. 

Respiratory tract conditions

Aberdeen diagnosed laryngeal chondritis in a six-month-old, pedigree Texel ram lamb. Coughing and wheezing at exercise was reported in the group of 24 lambs and shearling rams and the submitted lamb had suddenly deteriorated and died.  A large, deep necrotic lesion was found on the left laryngeal mucosa partly occluding the airway. The cause of death was massive intrathoracic haemorrhage thought to originate from the major vessels immediately cranial to the diaphragm. This may have been the result of breathing against an obstructed airway for a long period.

Ovine pulmonary adenocarcinoma (OPA) was diagnosed in two adult ewes submitted to Ayr as part of an investigation into ongoing losses in a mule flock. Approximately 30 ewes had died since turnout after lambing in the spring. They were either found dead or developed hyperpnoea and/or loss of condition prior to death.  Necropsy revealed large areas of white consolidated tissue especially in the antero-ventral lobes. Histopathological changes were consistent with extensive OPA and a concurrent acute, suppurative pneumonia.  Serological screening for evidence of exposure to maedi-visna was negative.