Nelson Marlborough Health is investigating two cases of salmonella gastroenteritis among farm workers in the Murchison area.
In a statement the Public Health Service said it understood the two cases were likely to have come from stock and workers have been advised.
Salmonella is the second most common bacterial cause of foodborne illness in New Zealand and can be picked up through contaminated food, water or contact with infected animals.
The disease can live in the gut of many farm animals and can contaminate meat, eggs, poultry and milk.
The Ministry for Primary Industries said it was not part of the investigation because it was being handled by the local district health board.
Federated Farmers said with school holidays underway it was a good time to remind farmers that they and their children needed to wash their hands before eating and keep vigilant with personal hygiene.
DairyNZ said if farmers were worried about the health of their animals, in particular those showing signs of diarrhoea, they should immediately contact their veterinarian.
It said said weather could contribute to outbreaks because bacteria was spread more easily in wet conditions, and wetter conditions could cause some animals stress, leading them to be more susceptible.