Research is still ongoing around the relatively new condition of summer scour syndrome, with many herds experiencing the condition in recent years.

The exact cause of summer scour is still unknown, however, there are a number of risk factors that are likely to cause the illness.

The disease is thought to be related to nutritional issues, such as the grass quality being offered to calves and an excessive intake of nitrogen (N), which leads to ammonia toxicity.

The rumen may be insufficiently developed to digest grass, as a calve’s grazing diet in the first year is a common denominator in all cases.

Summer scour syndrome

The condition sees calves experiencing dehydration, rapid weight loss, scour, lethargy, lack of rumination and weakness, which can ultimately, lead to death.

This can happen only a few weeks after turnout to grass, resulting in calves falling behind targets, which can be difficult to regain.

The disease often occurs when calves are grazing lush pastures with a high crude protein (CP) content (>20%) and a low fibre content (<40%).

If their rumen is not properly developed and they continue grazing the leafier parts of the grass which contain more nitrates and non-protein nitrogen (NPN), a large quantity of ammonia may build-up in the rumen.

Unstable pH is another knock-on effect of inadequate rumen development, which may lead to the calf getting summer scour.


There needs to be a gradual weaning for calves, with an appropriate transition from milk to grass.

In order to allow for rapid rumen development, concentrates should be added to the diet within the first week of life.

At four-weeks-of-age, the gradual weaning should begin, and prior to milk being stripped from the diet completely, calves should be eating 1kg of concentrates/day.

Making any dietary changes should be avoided as it will only cause stress on the calf and take the animal longer to adjust.

As calves are unable to handle high quality grass, it may be better for them to have access to more fibre, as calves that are grazing on more fibrous grass rarely suffer from the disease.

A practical way of correcting the fibre deficit for your calves, is to introduce hay or straw into the diet while the calves are out at grass.

It is important to keep this hay or straw fresh and to keep it in their diet for the first number of months out at grass.

Strip grazing calves is another possible method to prevent the onset of summer scour as it will encourage them to graze both the leaf and the stem of the grass.

It is crucial in the first four to six weeks after turnout to grass, to closely monitor your calves for any evidence of scour and weight loss so you can detect the condition early and treat accordingly.