Veterinary Services

Generalised and systemic conditions

Antibody to alcelaphine herpesvirus-1 was detected in a blood sample from a six-year-old Aberdeen Angus-cross cow that was anorexic and pyrexic. This virus is the causal agent of malignant catarrhal fever. The cow had not responded to antibiotics and developed multiple small patches of oedema of the skin in addition to ataxia and hyperaesthesia. Unusually, an improvement in the neurological signs was reported and the cow's appetite returned.

Four of a pen of 10, six-month-old Limousin calves died over a week. The right hind leg of the calf submitted to Dumfries was swollen from the hock to the hip due to emphysema found subcutaneously and between the muscles which were black. Fluorescent antibody tests (FAT) were positive for Clostridium chauvoei, which was also isolated from affected muscle confirming a diagnosis of blackleg.

SAC considered that septicaemia due to Listeria monocytogenes caused the death of a 10-day-old Aberdeen Angus cross Holstein Friesian calf submitted to Dumfries. At postmortem, the meninges appeared slightly cloudy and the navel thickened. Listeria monocytogenes was isolated from the liver and kidney. Calves were artificially reared in small group pens with no access to silage. Contaminated straw was suspected as a potential source of the organisms.

A three-week-old beef suckler calf submitted from a farm in Angus was the second calf to die suddenly on the farm in two days. At necropsy the mucous membranes were pale, and this was associated with a marked paleness of the skeletal musculature. Extensive areas of pale myocardial necrosis were apparent in the wall of the left ventricle and the inter-ventricular septum (figure 1 - see top right-hand side). The liver was enlarged and the kidneys congested. Streptococcus bovis was isolated from heart tissue while histological examination showed extensive fibrosis and mineralisation. Much of the myocardium encased by the fibrous tissue was undergoing coagulative necrosis. Histology of skeletal muscle found no evidence of abnormalities. These changes were consistent with infarction and scar tissue formation but white muscle disease could not be totally excluded.

Alimentary tract disorders

Johne’s disease was diagnosed on postmortem examination of a two-year-old Charolais-cross cow. The disease was previously seen on the farm but the cow's dam was 14-years-old and fit and healthy. The cow was in poor condition, dull, depressed and dehydrated with diarrhoea. At necropsy 90 per cent of the ileum was thickened and corrugated and Ziehl Nielsen stained smears showed numerous acid-alcohol fast bacilli consistent with Mycobacterium avium subsp. paratuberculosis.

A farm visit was carried out to investigate an outbreak of cryptosporidiosis on an Aberdeenshire unit that experienced a 58 per cent calf mortality rate in a batch of 24 suckler cows and calves, despite preventative treatment with halofuginone. A variety of other treatments were attempted but only one of the diarrhoeic calves survived. The herd had almost doubled in size to 100 cows in the space of one year but no additional accommodation had been provided. The SAC considered that the high stocking rate in the shed was a significant contributory factor together with chilling of the calves as the shed was open to the wind and rain.

Reproductive tract conditions

All centre received many submissions for bovine abortion investigation as the main spring calving season approached. Confirmed diagnoses were reached in 39 cases with 60 per cent of these diagnoses being Bacillus licheniformis, Listeriosis or fungal. This is consistent with the poor quality of silage and hay made during the wet summer last year.

Edinburgh diagnosed a combined infection with Bacillus licheniformis and fungi (suspect Aspergillus sp.) in a Limousin fetus, the first abortion in a group of heifers. The placenta was markedly thickened and covered in exudate. Unusually no fungal hyphae were seen in the stomach content and cultures were sterile but a moderate pure growth of Bacillus licheniformis was obtained from the placenta. Histopathology revealed a dramatic suppurative placentitis with vasculitis and numerous fungal hyphae consistent in morphology and staining characteristics with Aspergillus sp. No bacteria were seen but they could easily have been masked by the intense inflammation. Examination of the lung revealed a cellular infiltrate confirming fetal infection.

Twin foetuses with associated placenta were submitted for an abortion investigation from a beef unit in Perthshire. This was the first abortion in group of 50 cows being fed primarily on home-produced baled silage. No gross abnormalities were detected at necropsy however culture of placenta and foetal stomach contents yielded pure growths of Listeria monocytogenes, consistent with a diagnosis of listeriosis. Another Perthshire farm submitted a bovine foetus, the second abortion in the herd of out-wintered cows being fed silage and concentrates. Washing the contaminated placenta revealed numerous red spots spread across the membrane. Routine bacteriology yielded no significant bacterial growths, however antibody to Bovine Virus Diarrhoea (BVD) virus was detected in fetal fluids. Histological examination of the placenta showed a placentome with extensive mineralisation of the fetal component along with oedema and focal areas of coagulative necrosis. There was an apparent increase in cellularity of the maternal elements. These findings are not typical of bacterial or fungal infections but were consistent with the evidence of BVD challenge.

Nervous system disorders

A four-month-old, Holstein-cross calf submitted for necropsy was seen staggering and falling over three days previously. It was treated for cerebrocortical necrosis (CCN). At necropsy the cerebrospinal fluids (CSF) was slightly blood-tinged but no inflammatory cells were demonstrated on microscopic examination. The whole brain did not fluoresce under UV light but on further examination multiple, very discrete areas of fluorescence were found on cut surfaces of the coronal slices. Histological examination showed multiple areas of CCN, especially in the deep cerebral cortex on the border between the grey matter and the tips of the white matter. Necrotic neurones were present within many of these areas. The SAC considered that the unusual distribution of these lesions was consequence of the treatment given.