Veterinary Services

As a consequence of the exceptionally cold and snowy weather, many producers with out-wintered sheep were forced to introduce concentrate feeding.    The feeding of concentrates under such circumstances carries a particular risk of ruminal acidosis in animals unused to a carbohydrate rich diet.  These risks may be compounded when certain animals gain a disproportionate share of the ration due to a lack of trough space or an initial reluctance of others in the group to eat their share. Ruminal acidosis secondary to carbohydrate overload was confirmed on seven occasions.  Aberdeen examined the carcase of sheep that was humanely destroyed after being found recumbent in the lairage of a local market. The rumen was found to contain a large quantity of barley grains and the pH of the rumen liquor was 4.0. Four other animals from the group were found dead, and ruminal acidosis was considered the most likely cause of death in all five. 

Toxic conditions 

 
Three Shetland-cross ewes submitted to Dumfries for postmortem examination were among eight ewes found dead in a field they had been grazing for two weeks.  A further three ewes were euthanased and six more were recumbent. Rhododendron poisoning was confirmed when leaves were found in the rumens of all three ewes examined. Vomiting, said to be the classic sign of rhododendron poisoning in sheep, was not observed within the affected group.  The SAC C VS considered that the heavy snow had forced the sheep to graze the rhododendron plants that they would normally have avoided. 

Parasitic diseases

Parasitic gastroenteritis continued to be recorded by most centres during December.  Aberdeen confirmed the diagnosis in a group of 18-month-old Suffolk lambs that were treated at three-weekly intervals with anthelmintics from the benzimidazole and avermectin groups.  Advice was given on how to investigate the possibility of anthelmintic resistance.

Generalised and systemic conditions

The incidence of systemic pasteurellosis tends to fall in December, following the normal annual peak in diagnoses during the month of November.  2010 was no different, with three cases recorded by SAC C VS in December, after eight were diagnosed the previous month.  An eight-month-old mule hogg was submitted to Inverness following sudden death. Gross pathology was suggestive of septicaemia and Bibersteinia trehalosi was isolated from both lung and liver tissues.  In addition there was also a significant faecal worm egg count of 1,250 trichostrongyle eggs per gram.

Listeria monocytogenes was isolated from the spleen, liver, lung and kidney of a nine-month-old hogg submitted to Thurso. Listeriosis is commonly associated with feeding of spoiled conserved forage.

Review of Clostridial Disease in Sheep

Clostridial disease accounted for approximately nine per cent of all diagnosable submissions in sheep submitted to SAC C VS between 2005 and 2010. Clostridium perfringens type B and Clostridium perfringens type D are the most commonly identified causative agents (Figure 4 - see top right-hand side). The low incidence of Clostridium sordellii should be interpreted with caution as specific diagnostic criteria allowing accurate recording of cases only began in 2009. Clostridium sordellii is the causative agent of abomasitis in lambs aged four to ten-weeks-old, and toxaemia in older sheep. Clostridium perfringens type B is the causative agent of lamb dysentery which typically causes bloody diarrhoea and death in lambs less than three weeks of age. Clostridium perfringens type D is the causative agent of enterotoxaemia and pulpy kidney which usually presents as sudden death in older lambs. The seasonal variation in Clostridium species diagnoses is marked (Figure 5 - see top right-hand side). As expected, the peak incidence of Clostridium perfringens type B is centered on the spring lambing period. Clostridium perfringens type D is diagnosed all year round, however there is also a notable upsurge of cases during the spring. The reasons for this seasonality are not well defined but reinforce the need to ensure vaccination programs are adequate at this time of year. Flock health plans should ensure that pregnant sheep are vaccinated with a multivalent Clostridium species vaccine prior to lambing to optimize protection of lambs. A follow-up primary vaccination course is essential for growing lambs. Year-old hoggs and tups are often forgotten about at this time of year and their booster vaccinations should be highlighted in flock health plans to ensure ongoing protective immunity.

Respiratory tract conditions

A Scottish blackface ram, purchased as a lamb twelve months earlier, was in poor body condition following the mating period.  The ram subsequently died and the necropsy revealed areas of both lungs that were grey in colour and firmly consolidated.  Ovine pulmonary adenocarcinoma (OPA) was confirmed on histopathology.  In contrast a six-year-old mule ewe submitted to Edinburgh died suddenly in good bodily condition.  This was the fourth ewe to be lost in a two day period from group of 380.  In this case necropsy revealed a severe suppurative pneumonia and pleurisy, superimposed upon a number of pale firm nodules within the lung.  A pure growth of Mannheimia haemolytica was isolated and an underlying OPA was again confirmed by the histopathologist. These two cases illustrate the two most common clinical presentations of disease due to OPA and the most common necropsy findings.

Skin diseases

 
Samples of wool and scab material were received at Dumfries from a greyface ewe with scaling alopecic areas on the face. Trichophyton verrucosum, the most common cause of ovine ringworm, was isolated on dermatophyte culture.

Periorbital eczema was diagnosed in a ram with a head abscess from which a pure growth of Staphylococcus aureus was isolated. This condition is an uncommon diagnosis in Scotland with only two cases recorded during 2010.