Yersiniosis in Deer
Yersiniosis remains one of the most significant health risks for weaner deer in New Zealand, particularly during late autumn and winter. In regions such as Marlborough, where deer commonly face weaning stress, cold snaps, variable feed supply, and yarding for management, the disease can cause sudden and severe losses if unmanaged. Visit deernz.org for more info.
Vaccinating weaner deer with Yersiniavax® is a proven, cost-effective strategy to reduce mortality, improve growth performance, and protect enterprise profitability.
What Is Yersiniosis?
Yersiniosis in deer is caused primarily by the bacterium Yersinia pseudotuberculosis. It is one of the most serious and common infectious diseases of farmed deer in New Zealand and has been well recognised since the late 1970s.
The organism is widespread in soil, water, and pasture and is carried by many species, including deer, sheep, cattle, pigs, birds, rabbits, and rodents. Carrier animals often appear healthy but shed the bacteria in their faeces, contaminating the farm environment.
Why Marlborough Deer Farms Are at Risk
Marlborough deer systems commonly face several factors that increase susceptibility to yersiniosis:
Weaning stress, particularly when coinciding with yarding or transport
Cold, wet or windy weather during autumn and early winter
Sudden changes in feed quality
Internal parasite burdens
Mixing of unfamiliar mobs during management events
Yersiniosis is considered a stress-triggered disease. While most deer are exposed to Yersinia early in life, clinical disease develops when stress suppresses gut motility and immune function, allowing the bacteria to multiply and produce toxins that damage the intestinal lining.
Clinical Signs and Production Losses
Yersiniosis typically affects young deer aged 4–8 months, often during their first autumn and winter.
Common signs include:
Dullness and isolation from the mob
Reduced appetite or failure to eat
Green watery diarrhoea, progressing to dark or bloody scour
Staining around the hocks and tail
Rapid dehydration and weakness
In some cases, deer are found dead with little or no warning, especially during acute outbreaks.
Impact on Herd Performance
10–30% losses are commonly reported in unvaccinated herds
Up to 30% of a mob can be affected during an outbreak
Survivors often suffer longterm growth setbacks, reducing venison returns.
Why Vaccination Is Critical
Once an outbreak begins, it is too late to vaccinate and control relies on whole-mob antibiotic treatment, fluids, and shelter, which is labour-intensive and costly. Vaccination is therefore best viewed as preventative risk management, not emergency response.
Benefits of Vaccinating with Yersiniavax®
Yersiniavax® is a deer-specific vaccine containing inactivated Yersinia pseudotuberculosis serotypes relevant to New Zealand conditions.
Proven Benefits:
Significantly reduces mortality and severity of disease
Decreases the number of clinically affected deer
Reduces growth setbacks in surviving animals
Lowers reliance on antibiotics during outbreaks
Field data show vaccination can reduce losses to 3% or less, compared with up to 30% in unvaccinated mobs.
From an economic perspective, vaccination becomes costeffective when just one weaner is saved for every 40 vaccinated, before accounting for veterinary and labour costs associated with outbreaks.
Yersiniavax® Dosage and Vaccination Programme
Dosage and Administration
Dose: 2 mL per deer
Route: Subcutaneous (SC) injection
Site: Anterior (front) half of the neck
Vaccination Schedule
Two doses required, 3–6 weeks apart
Weaners must be at least 12 weeks old at the first vaccination
Vaccination should be completed at least 2 weeks before the high-risk period (late autumn/winter)
Timing for Marlborough Systems
Ideally, vaccinate before or at weaning, and before significant weather or feed stress
If vaccinating younger fawns (<12 weeks), a third dose may be required for adequate protection.
Integrating Vaccination with Good Management
Vaccination works best when combined with stress reduction strategies:
Provide quality feed and gradual feed transitions
Ensure adequate shelter from wind and rain
Minimise time in yards
Control internal parasites
Avoid unnecessary transport during high-risk periods
Conclusion
Yersiniosis remains the leading cause of death in weaner deer in New Zealand, and Marlborough farms are not immune. Because the bacteria are always present in the environment, prevention through vaccination is the most reliable way to protect young deer.
Strategic vaccination of weaners with Yersiniavax®, alongside sound management, delivers lower mortality, better growth performance, and greater confidence through autumn and winter.
For more information, please visit deernz.org.
