A mystery illness which struck dairy herds this spring is the subject of an active investigation by milk processors.

The health condition impacted herds right across Munster and south Leinster, with most milk processors in the region reporting cases among their suppliers.

The symptoms varied across farms. Some animals showed physical signs of ill health, with grass tetany and milk-fever-like symptoms. Bad scour, along with a severe lethargy and lack of energy, were also noted in a number of affected herds.

However, most normal animal health diseases were ruled out upon veterinary inspection.


The condition resulted in cows generally suffering a sudden drop in milk yields for a week to 10 days. This ranged from 10-20% of output, or 4-6l per cow per day. However, some cows that were badly affected went dry.

Industry sources said that while it was difficult to gauge exactly how many farmers were affected, anecdotal evidence suggests that the figure could be in excess of 100.

Although the ailment has not been officially identified and named, one farmer maintained that it was like “COVID for cows”.

Others have referred to it as the “winter cow syndrome” as it seemed to occur when cows changed from a winter diet of mostly silage and meal to a spring diet of grass and meal.


It has been suggested that the wet weather exacerbated the changeover this spring.

The situation seemed to improve after herds were fed higher levels of silage in the diet.

“It knocked milk output by 10-20% over the week that the herd had it,” one Limerick farmer told the Irish Farmers Journal.

“It really pinched the peak,” he added.