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Catherina Cunnane
Catherina Cunnane
Catherina Cunnane hails from a sixth-generation drystock and specialised pedigree suckler enterprise in Co. Mayo. She currently holds the positions of editor and general manager at That's Farming, having joined the firm during its start-up phase in 2015.
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What is Summer Scour Syndrome?

Summer Scour Syndrome is a relatively new condition and has not yet been widely researched, according to Michelle McGrath of AHI (Animal Health Ireland).

But, it is a collection of clinical signs, characterised by scour and rapid weight loss, lethargy, lack of rumination and weakness, which can progress to profound weakness and death.

Some calves may develop oral and oesophageal ulceration or ulceration of the muzzle.

Other infections or infestations that cause similar signs in calves at grass have been ruled out before a diagnosis can be made.

These include:

  • Coccidiosis (blood scour);
  • A high worm burden;
  • Mineral issues such as molybdenum toxicity (with or without concurrent copper deficiency);
  • Copper toxicity;
  • Rumen acidosis (from heavy concentrate feeding);
  • Salmonellosis;
  • BVD (Bovine Viral Diarrhoea).

McGrath outlines that your veterinary practitioner can distinguish between these diseases and summer scour.

She comments, in the body’s technical calf health programme bulletin, that “not all calves in the group are affected, and severity can vary from year to year and farm to farm”.

“It typically occurs in dairy calves within a month of turnout to grass and up to 12 months of age,” she added.


The cause, according to McGrath, is not “definitively known”, and several theories exist as to what the most likely risk factors are.

An infectious cause has not yet been identified, and the disease is thought to relate to nutritional issues, such as when the rumen is insufficiently developed to digest forage, as the one factor common to all cases is a grazing diet (exclusively or partially) in the calves’ first year.

Lush pastures

Summer Scour Syndrome is more common in calves grazing ‘lush’ pastures, typically with a high crude protein (greater than 20%) and low fibre (less than 40%) content per kg of dry matter ingested.

It is suspected that if the rumen has not developed properly, it makes it difficult for calves to deal with a fresh grass diet.

Calves, by nature, are selective grazers and preferentially consume the top, leafier parts of the grass, which contain more nitrates and non-protein nitrogen (NPN).

The consumption of large quantities of nitrates and NPN by young calves with an immature rumen may lead to an excessive build-up of ammonia in the rumen.

Moreover, inadequate rumen development may also lead to an unstable pH for rumen bacteria to function properly, which may potentially contribute to the syndrome.

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