Yersiniosis, a highly infectious disease, is characterised by a bloody scour in deer fawns which rapidly leads to death if untreated. Early clinical signs of the disease in deer include a green, watery, smelly diarrhoea which soon becomes bloody.

What causes Yersiniosis?

• Yersiniosis is caused by a bacterium called Yersinia pseudotuberculosis which can be carried by wildlife (birds, rodents, rabbits and hares) as well as domestic animals (cattle, sheep, pigs and goats).
• Carrier animals usually remain healthy although they secrete the organisms in their faeces.
• The bacterium survives well in soil, water and pasture during the winter months.
• Because the bacterium is widespread in the environment it is highly likely that fawns will be exposed to it.

Yersiniosis is stress related

• New Zealand experience has shown the disease is much more prevalent in late autumn and winter, and that its onset may be triggered when deer are exposed to stress.
• Typical stresses are poor nutrition, sudden change in feed, mixing of deer groups, snow storms, cold wet windy weather, yarding, transport and heavy parasite burdens.
• Some or all of these stresses may occur at, or soon after weaning, in addition to the stress of weaning itself.
• Particularly severe stress occurs in deer that are weaned, sold and transported to new properties all at once. The weaners have no time to adjust to their new environment and become extremely susceptible to disease.

How is bad weather involved?

• In bad weather fawns can lose a lot of body heat very quickly because they have very low fat reserves and their coats do not provide good insulation.
• Bad weather also causes fawns to stop eating, seek shelter and lie low. If bad weather continues, the fawns’ low food intake can cause their intestinal movements to slow down, and a reduction in heat production. This compounds the heat loss due to bad weather.
• The slowing of the intestinal activity allows Yersinia organisms to multiply excessively and produce toxins which damage the lining of the intestines.
• This leads to rapid loss of body fluids, bleeding into the intestines, and dehydration and shock, and frequently results in death of the affected animal.

What can the farmer do?

If exposed fawns are healthy, well-fed, and not burdened by parasites or subjected to abnormal stress, the infection will probably be mild and not noticed. However, if the fawns are stressed at the time of infection, then they may develop diarrhoea and are likely to die if untreated.

Farmers should:

• Aim to reduce the effects of common stresses
• Vaccinate with Yersiniavax vaccine to prevent clinical disease
• Use Yersiniavax to enhance, rather than as a substitute for good management

Remember: it is too late to vaccinate once an outbreak of Yersiniosis has started.

Ideally you should try to plan your vaccinations so that the fawns receive 2 shots of Yersiniavax 3 to 6 weeks apart, with these completed at least one week before weaning.