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April 2009 RVL Monthly Report

Cattle

A one-month old calf was submitted to Athlone with a history of flaccid paralysis of the hind legs. It had responded briefly to treatment before being euthanased by the attending veterinary practitioner. On gross examination the meninges were only mildly congested but opening the lumbar spinal column revealed abscessation of the intervertebral space and osteomyelitis of the vertebrae. Mannheimia haemolyica was isolated from the lesion. A one-month old Limousin calf with a history of pneumonia and coccidiosis was submitted to Athlone. Gross post mortem examination revealed lesions of bronchopneumonia from which M. haemolytica was isolated. Kilkenny isolated M. haemolytica from lung, heart and liver of a ten-week old calf submitted with a history of chronic cough. It had the classical gross lesions of pasteurellosis- fibrinous pleuritis, pericarditis and pneumonia (figure 1).

 

Fibrinous pleuritis and marbling of lung

Figure 1: Fibrinous pleuritis and marbling of lung tissue in a ten-week old calf with Mannheimia haemolytica-associated pneumonia (photo: Donal Toolan).

Clostridium chauvoeii was identified by Kilkenny in a blackleg lesion from a five-month old weanling. Four other weanlings had also died suddenly on the farm.

Limerick diagnosed ragwort poisoning in a yearling bullock.  This was the second animal to die from a group of five which had been bought in a mart less than three weeks previously.  The presenting signs were tenesmus, hind limb weakness and evidence of severe pain. The chronology of events in this case presented issues relative to the timing and amounts of toxin ingested. Sligo also reported two cases of ragwort poisoning during the month, both affecting adult cattle.

Athlone visited a beef unit to investigate the occurrence of neck and shoulder abscesses on cattle housed on slats. Up to 25 per cent of 130 bullocks were affected at the time of the visit. This was the third year of the problem. A suspect TB lesion collected previously from one of the animals at slaughter cultured positive for Actinobacillus lignieresii and negative for Mycobacterium bovis. Many of the animals were examined during the farm visit and most were found to have abscessation of the submandibular lymph nodes but no evidence of tongue lesions. Serum copper and selenium levels were analysed and discovered to be very low in all animals sampled. It was suspected that the very low mineral levels may have had some effect on immunity, and that this, coupled with the mixing of clean and infected animals, was at the heart of the problem. Advice was also given regarding appropriate disinfection of the house, paying particular attention to areas where animals would be inclined to scratch. As all animals are to be sent to the factory in the autumn, it was considered that thorough disinfection at that time could break the cycle of infection.

A twenty-month old housed heifer was submitted to Athlone, the second to die in a two-day period. It had a history of being down shortly before death and was unable to get up. On gross post mortem examination, there were subcutaenous haemorrhages (contusions). Blackleg lesions were sought but none were found. Virology for respiratory viruses was negative. Parasitology showed a moderate strongyle burden, and fluke eggs were present. Tissue lead was within the normal range. Analysis of the vitreous humour showed the magnesium concentration to be low (0.25 mmol/L), indicating this animal was hypomagnesaemic. Values less than 0.25mmol/L are consistent with hypomagnesaemia, but magnesium concentration tends to rise after death, up to 50% higher at 72 hours post mortem. Hypomagnesaemia was therefore suspected to be the cause of death. In housed animals hypomagnesaemia is unusual, but plasma magnesium concentration is dependent on adequate dry matter intake, so reduced feed intake can be a risk factor, particularly if the animal is stressed.

Caudal vena cava thrombosis with pulmonary thromboembolism was diagnosed by Dublin in a two-year-old Charolais bullock that died suddenly. A suppurative tenosynovitis of the superficial digital flexor tendon of the right hind limb was also diagnosed in this bullock. The animal had previously been treated for lameness and suspected pneumonia.

Athlone examined a dairy cow with a history of staggering and depression within two days of calving. On gross examination the cow had a large fluid-filled and oedematous uterus. Salmonella dublin was isolated from the a swab of the endometrial surface. The gross and bacteriological findings indicated a diagnosis of septic metritis due to Salmonella dublin infection, with evidence of systemic consequences (septicaemia).

Sligo was asked to investigate weight loss, retained placentas and reduced milk yield in a 100-cow dairy herd.  It became apparent early in the investigation that low fertility and poor milk solids were also issues for this herd.  Ketosis was diagnosed in cows in the first week of lactation. The milk recording data and the loose faecal consistency suggested acidosis.  While the cows were fed a low level of concentrates in late pregnancy to adapt the rumen flora, cows were still becoming acidotic post-calving. It was noted that the diet contained very little fibre and that cows in early lactation were hypocalcemic and hyposelenaemic.  All of these factors were considered to be contributing to the retained placenta and poor production problems.

Sheep

Border disease was diagnosed by Sligo in two newborn lambs.  The owner reported a lack of coordination in affected lambs, but had also noted that many of the lambs in this years crop had appeared to have poor resistance to disease.

A lamb was presented to Athlone with a history of scour, rapid deterioration and death. There was no history of nervous signs. On gross examination there was consolidation of a small area of the lung and scant amounts of white/yellow faeces. Listeria monocytogenes was isolated from multiple organs. Histology showed non suppurative interstitial pneumonia and suppurative interstitial nephritis. L. monocytogenes was also isolated by Dublin from a four-week old lamb with lesions of suppurative meningoencephalitis. There had been three similar lamb deaths in this flock prior to this case. The distribution of the lesions in the medulla, and the isolation of the bacterium only from a meningeal swab suggested a pathogenesis of ascending infection from the peripheral nerves rather than blood borne spread, which is not common in young lambs.

A store lamb was presented to Sligo with severe lameness. Most of the flock were affected to some extent. The condition had started when the lambs were at grass last autumn, and had deteriorated substantially after housing.  Fusobacerium necophorum was cultured from the foot lesions and spirochaetes were identified on histopathology. The farmer reported that he had used a foot rot vaccine on later arrivals to the flock and that these lambs were not affected as badly. 

A one-year old hogget was presented to Athlone with a history of pining. On gross examination there were lesions of diffuse pneumonia with consolidation of the apical and cardiac lobes. A large amount of froth was present in the airways and lungworm larvae were also visible. Faecal parasitology identified a strongyle count in excess of 50,000 eggs per gram, and Mannheimia haemolytica was also isolated from the lung.

A seven-year old ewe, noticed ill in the morning, died rapidly and was presented to Kilkenny. The liver was enlarged and had a distinctly lobular pattern. Haemoglobinuria was also present. Copper poisoning was diagnosed based on the demonstration of a liver copper level of 6.2mmol/Kg wet matter (normal range 0.06 to 2.5mmol/Kg) and on the histological changes seen in the liver.

Pigs

Two ten-week old pigs were submitted to Limerick with a history of sudden death. Both animals had similar lesions- polyserositis and bronchopneumonia. Haemophilus parasuis was isolated. Actinobacillus (formerly Haemophilus) pleuropneumoniae was isolated from a group of three-month old pigs submitted to Kilkenny from a unit reporting a high incidence of respiratory disease. Severe lesions of pleuropneumonia and large focal areas of consolidation were found at post mortem (figure 2).

 

Pleuropneumonia associated with A. pleuropneumoniae

Figure 2: Pleuropneumonia in a three-month old pig associated with Actinobacillus pleuropneumoniae infection (photo: Donal Toolan).

An eleven-week old pig discovered in severe respiratory distress was euthanased and submitted to Kilkenny. It had a diaphragmatic hernia, with the stomach and anterior small intestine situated within the thoracic cavity.

Other Species

Equine herpesvirus type 1 was detected in an equine foetus that was submitted to Limerick.

A heavily pregnant goat was submitted to Limerick from a herd experiencing an increased level of late-term abortions and adult mortalities. On examination the goat was pregnant with twins and was in a fat condition. However the liver was enlarged, pale and greasy to touch. Listeria monocytogenes was isolated from the brain. Histopathology confirmed fatty liver and listeriosis. It is likely that feed management in the latter third of pregnancy was inadequate to provide for the needs of the goats on this farm. Poor quality baled silage was being fed. Advice was given on the necessity to improve the diet quality.

Kilkenny diagnosed amyloidosis in an emaciated mute swan (Cygnus olor) that was euthanased in-extremis. Amyloid deposits were seen histologically in liver, kidney and spleen. Amyloidosis occurs in association with a number of chronic primary diseases and can be induced by repeated exposure to Salmonella typhimurium, Escherichia coli or endotoxin. Amyloidosis in domestic ducks has been related overcrowding or social stress. Chronic and repeated exposure to bacteria or endotoxin that could occur under such circumstances, is thought to be a major contributing factor. (Wobeser, 1997)

Reference

Wobeser G. A. (1997): Diseases of Wild Waterfowl. 2nd edition. Plenum Press, New York.