Salmonellosis can cause considerable discomfort for cows and farmers alike. It’s a common disease causing acute diarrhoea and is mainly caused by ingestion of Salmonella bacteria from contaminated environments, infected water and feed.
Rates of the disease have been increasing on dairy farms. While Salmonella Typhimurium is the main serotype, the Ministry for Primary Industries found new serotypes of Salmonella emerged at alarming rates in cattle between 2013 and 2020, particularly S. Bovismorbificans and S. Give. This trend was also reflected in surveillance data of gastrointestinal disease in the human population.
Over the 2021 and 2022 dairy seasons, researchers from Massey University’s EpiCentre led a study among dairy farms aimed at better understanding the impact of salmonellosis outbreaks and to identify management factors that might increase the risk of outbreaks occurring.
Fifty-four farmers with salmonellosis outbreaks (10 or more animals affected) were enrolled in the study after invitation by their vets. Fonterra helped with enrolment of a comparison control group of 119 farmer suppliers not affected by the disease.
Key findings
Over the study period, one in 20 dairy herds experienced a salmonellosis outbreak. Calves were the most severely impacted with 30% experiencing illness and 5% dying from the disease. A few farms in the study had all of their calves affected by the outbreak.
Farmers reported on average 5-10% of heifers or cows had scours or aborted and 1-2% died in outbreaks in these age groups.
One quarter of the outbreaks involved multiple management groups, commonly including calves, as well as cows.
Risk of a farm experiencing a salmonellosis outbreak increased with higher stocking rates and larger herd size, e.g. for each increase in herd size by 100 cows the risk increased by 20%.
Farms with wild animals present on the property, such as deer or gulls, tripled the risk of an outbreak.
Key recommendations
Taking steps to reduce the risk of Salmonella outbreak on-farm allows farmers to protect animal welfare, reduce production impacts and safeguard the health of farm workers, their families, and the general public.
The research recommends owners and key decision makers of dairy farms:
- Discuss with their vet how they can implement biosecurity to control salmonellosis
- Implement effective control programmes for wild animals
- Vaccinate heifers and cows before they calve.
In the event of an outbreak, farm teams should:
- Dispose safely of infected material e.g. aborted calves or foetal membranes or contaminated calf bedding
- Clean and disinfect personal protective or other equipment with an effective product immediately after leaving an affected group
- Isolate affected animals or their group from others on the farm to avoid spreading salmonellosis, especially to calves
- Above all, maintain strict personal hygiene among all people coming into contact with animals, particularly old or very young people.
For further information about the study and its results and recommendations visit sites.massey.ac.nz/salmonella.