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Systemic Pasteurellosis in Lambs

25 November 2022

This year there have been increased outbreaks of systemic Pasteurellosis.  While the reasons are unclear, warm wet Autumn weather may have led to increased pasture worm burdens and prolonged tick activity which, when combined with routine husbandry procedures and/or changeable weather, can increase disease outbreaks.

Systemic Pasteurellosis is a common cause of death in weaned lambs between September and December. This bacteria is found in the throat and tonsils of sheep, however periods of ‘stress’ can lead to septicaemia and the death of affected lambs.  Lambs are most commonly found dead with no period of ill health. Mortality can be high with losses of 20-50% reported but is more commonly around 2% in most outbreaks.

The ‘stresses’ associated with systemic Pasteurellosis include weaning, handling, transport, mixing, movement to good grazing, and change to cold, wet weather.  It is not uncommon to find that lambs which have died of systemic Pasteurellosis also have other conditions which may be contributing to their ‘stress’; these include worm burdens, fluke burdens, tick-borne fever and selenium and/or cobalt deficiency.


Diagnosis is by post-mortem examination. However, sampling faeces for WEC and some fresh liver for trace element analysis can be useful in identifying some predisposing conditions.


Pasteurella strains are included in many multivalent clostridial vaccines or as standalone Pasteurella vaccine. However, it should be noted that vaccines are unlikely to be completely protective in the face of significant stress. Prevention of systemic Pasteurellosis also relies on controlling the controllables and reducing the stresses on weaned lambs whenever possible.


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