Veterinary Services

Nutritional and metabolic disorders

Three seven-month-old Cheviot cross lambs were found dead within a week of moving from a grass field onto stubble turnips. Some within the group were described as appearing sleepy, while others also showed signs of scouring. Necropsy of one lamb at Dumfries confirmed the scour and revealed a pale, friable liver. Hepatic vitamin B12 content was <0.1 ug/g wet weight (normal range >0.19 ug/g wet weight) and histopathology confirmed changes typical of ovine white liver disease. In addition, histopathology of the brain revealed mild to moderate spongy change, consistent with hepatic encephalopathy.

Parasitic diseases

A Suffolk gimmer was submitted to Dumfries from a group of gimmers suffering ill thrift and deaths. The affected animal had a history of fluid faeces and weight loss over several months, despite a good appetite. The group received anthelmintic treatment in June 2007, and since then had run at grass with no supplementary feeding. Ascites and a pericardial effusion were found on necropsy together with severe hyperplasia of the abomasal mucosa. However only 2,250 trichostrongyle species worms were identified within the abomasum. Subsequent blood biochemistry supported these findings with serum pepsinogen 2.4 iu/l (normal range <1 iu/l) and albumin 22g/l (normal range 28-34 g/l). Histopathology indicated that there had been a severe parasitic challenge affecting the abomasum and small intestine, and suggested that if only one animal had been affected then the changes could have been put down to an individual idiosyncratic reaction.

Perth received two live lambs with a history of chronic scour and ill thrift. Both were in poor bodily condition with evidence of ascites and pleural effusion and a fibrinous discharge was present over the capsule of the liver along with fibrous scarring throughout the hepatic parenchyma. Histopathology confirmed liver changes indicative of very recent fasciolosis. In addition changes in the abomasal and small intestinal mucosa indicated a severe parasitic gastro-enteritis, sufficient to explain the chronic ill thrift.

Chronic fasciolosis was diagnosed on 21 occasions this month, while only one outbreak of acute fasciolosis was recorded. This compares to three and five diagnoses respectively, over the same period last year. The SAC VS suggests that while conditions may not have favoured the appearance of the acute form of fasciolosis this winter more flocks were exposed to the parasite. One Ayrshire farm reported six deaths over a period of 10 days, with the affected group of ewes showing anorexia, pallor and weight loss at housing. Postmortem examination of an affected animal revealed many adult Fasciola hepatica in the hepato-biliary tree and severe liver pathology. Concurrent Clostridium novyi infection (black disease) was also evident in this flock. No anthelmintic treatment had been administered. On another farm deaths and clinical disease occurred despite flukicide treatment, and triclabendazole resistance was suspected from investigation of faecal samples and submitted blood samples. Vitamin B12 deficiency was also detected in that flock.

Anecdotal reports from veterinary practitioners and shepherds suggest that the sheep tick (Ixodes ricinus) is now seen in larger numbers and for a longer period during the year in many flocks than previously. The presence of ticks on a carcase at necropsy is frequently regarded as an incidental finding and historical data is difficult to interpret. However, the analysis of data on tick-borne disease in sheep supports this contention. In particular the diagnosis of louping ill in Scottish flocks has shown an upward trend in the over the last 15 years (figure 4 - please see top right-hand side). Most cases in Scotland are recorded between the months of April and October, with a clear spring and autumn peaks apparent (figure 5 - please see top right-hand side). This reflects the most important periods of tick questing and feeding, and the fact that the parasite remains inactive while average temperatures are less than 7°C. While tick pyaemia is a relatively uncommon laboratory diagnosis it also shows a marked seasonal distribution, as young spring-born lambs are exposed to ticks of the first time (figure 6 - please see top right-hand side). Similar analysis of data on tick borne fever (TBF) as a cause of disease in sheep would be expected to show a similar trend. However, collection of information on the prevalence of this condition was hindered by the lack of a readily available, serological test to detect antibody to Anaplasma phagocytophilum, that left the examination of blood films for parasitaemia as the only diagnostic test available. Since TBF often predisposes the affected animal to other conditions, the diagnosis of acute infection is certain to underestimate its actual effect on overall sheep health. The distribution of outbreaks of louping ill and tick pyaemia cases across Scotland is shown in figure 7(please see top right-hand side).

Generalised and systemic conditions

Three lamb carcases were submitted from a Suffolk flock in Aberdeenshire to investigate the deaths of ten of the 40 neonates born during the first week of lambing. While some of the affected lambs were born up to one week prematurely, others were normal for the first 24 hours but suddenly deteriorated and died thereafter. Septicaemia due to Mannheimia haemolytica was found in two lambs and the third showed evidence of dystocia. While the measurement of ZST in the two septicaemic lambs was normal, the third had a ZST level of 4 units (reference range >14 units), consistent with an insufficient intake of colostrum. The lambing ewes had received a multivalent booster vaccination five weeks before lambing and concern was expressed that M. haemolytica septicaemia was diagnosed in young lambs. The SAC VS advised the vaccination programme be reviewed and should include consideration of the timing of boosters and vaccine handling and storage.

Reproductive tract conditions

Two abortions occurred in an Aberdeenshire flock of 70 Charollais ewes, which were due to start lambing three to four weeks later. Material submitted from the second case was positive for toxoplasmosis. Foetuses were submitted from two housed ewes in another local flock of 200 pure Suffolk and cross Charollais ewes. On this occasion Salmonella Derby was isolated on culture from the foetal stomach contents and placentae of each lamb. Within a week there were a further 15-16 abortions and 16 of the twin-bearing ewes that aborted died despite antibiotic treatment. The flock was treated with long-acting amoxycillin and no further abortions or stillbirths occurred. However the SAC VS suspected that the outbreak would have ceased in any event. This was because all the aborted and stillborn lambs were autolytic and ewes about to abort would have aborted in the days following treatment. Further investigations identified wild birds as the likely source of the infection. Salmonella Derby was isolated from bird faeces on a feed trough in the field where the twin-bearing ewes were kept before being housed. Ten of 12 randomly collected faecal samples from ewes were positive for S. Derby two weeks after the last abortion had occurred.

Border disease was suspected following nine abortions in a pedigree Suffolk flock due to start lambing in early January. No abortefacient pathogens were recovered from a batch of aborted lambs submitted and screening for Chlamydophila and Toxoplasma proved negative. However, neuro-histopathological examination showed that the brain of an affected lamb was moderately congested with gliosis in the tips of the corona radiata and apparent paucity of myelin in the same area. These changes, although not pathognomonic, where felt to be consistent with infection by border disease virus. However a subsequent assessment of maternal serology failed to identify any evidence of exposure to this virus.

Skin diseases

Thurso diagnosed sheep scab in ewes that were treated with an injectable avermectin six weeks previously. The animals had been returned to the same grazing after treatment.