Research continues to help better understand the intersection of management and the nutritional quality of milk. Driven by the Ireland dairy industry's interest in supporting the export market, food scientists Andre Brodkorb and Mark Timlin collected milk samples from three herds for the entire lactation to accurately assess the change.

“Our goal was to determine if there is a way to distinguish between the feeding regime,” said Brodkorb, research officer for Teagasc Food Research Centre. “Over 90% of our milk is exported, so understanding the changes in the milk due to feeding and the impact on dairy product processing has a huge economic impact on our industry.”

To distinguish the difference, the team fed three rations:

  • Grass-based: 95% Perennial ryegrass
  • Total mixed ration (TMR): 40% concentrate, 40% maize silage, 20% grass silage
  • Partial mixed ration (PMR): Grazing during the day, TMR in the evening

This project was discussed during the August edition of “Dairy Science Digest,” a podcast created by the University of Missouri.

The Irish way of dairying

Ireland recently initiated the “Grass-Fed Standard” for Irish dairy products which specifies the minimum number of days on pasture and requires grass inclusion at a minimum of 90% of the cow’s diet for truth in labeling purposes.

“Ninety-nine percent of farmers in Ireland should be able to produce milk for this grass-based standard thanks to the luscious green grass so easily grown here in Ireland,” Timlin explained. “The low cost of production promotes seasonal calving, with approximately 87% of all cows calving in between January and April of the year to capture the ideal growing conditions.”

Dairy fat for life

For decades, fat from dairy has received lowered nutritional ratings because of the high concentration of trans saturated fat, commonly known as bad fat. However, more recently scientists have become increasingly aware of how these fats digest or break down in the human body, resulting in a general consensus of it being fine in moderation. There’s growing research interest in the benefit of dairy fats in the human diet.

“We were interested in understanding the overall change in fatty acid profile in grass-based milk over those produced in the TMR system,” explained Brodkorb. “A class of unsaturated fatty acids of specific interest is conjugated linoleic acid or CLA.” CLA has been associated with heart health, anti-carcinogenic, anti-hypertensive anti-diabetic.

“Grass is naturally higher in alpha linolenic, and a lower proportion of linoleic acid then the likes of maize,” explained Timlin. “When the diet is high in grass, CLA spills over into blood of the cow and fuels the elevated concentration found in her milk.”

Fatty acid changes found with grass-based milk versus TMR were as follows:

  • Nineteen of the 22 different fatty acids analyzed were statistically different
  • 141% jump in CLA, with the peak increase in August
  • 83% omega-3 unsaturated fatty acid, or the “good fat”
  • Overall unsaturated fatty acids index rose 14% in milk derived from grass-based dairy

Noting the changes

Ultimately, grass-based milk yields approximately half the volume of typical U.S. TMR-based production systems. To ensure this management system remains profitable, the Irish dairymen seek to identify quantifiable changes the processor could use to validate the management system is being honored.

This differentiation would allow the processors to market grass-based milk at an advantage. The shared profit would support the grazing herds, which are currently declining.

The shift in macronutrients and fatty acid concentration shows the grass and PMR ration does change the composition of the milk.

The research milk collected was processed in the pilot plant into common Irish dairy products — butter, cheese, and whole milk powder. Key industry parameters, such as heat coagulation time and milk fat globular size were also assessed. These parameters ensure that grass-based milk is ideal for ultrahigh temperature (UHT) or shelf-stable milk and butter production.

There is an ongoing human intervention trial assessing the change in blood profile for individuals consuming dairy products from grass-based milk.

For those who are able to produce milk using a grass-based system, this differentiation is critical to market access. These findings were captured over the entire lactation, not just a snapshot of time to ensure no seasonal bias occurred. To learn more, listen to the “Dairy Science Digest” on your favorite podcast platform or read the full open access article in the Journal of Dairy Science at:

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(c) Hoard's Dairyman Intel 2023
August 24, 2023

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