What Influences C15:0 Content in Milk?

Healthy Aging

Why C15:0 Content in Dairy Fat Varies: Temperature, Feed, and Time

A new study looked at potential changes in the nutrient content of milk from black bengal goats in Thailand, based on seasonal changes in temperature. Now, while you may neither drink milk from black bengal goats nor live in Thailand, this study showed something that keeps popping up: the amount of C15:0 in full-fat milk, whether in Thailand goats or Irish cows, can vary significantly based on diet and season. Let’s dive into these studies to better understand just how much a few months in a year can influence how much C15:0 we may get from dairy fat.

C15:0 from goats in Thailand…

The most recent study from Buranakarl et al. measured nutrients in colostrum from goats during either cold or hot seasons of the year. Importantly, these goats were fed the exact same diets throughout the year. The average temperature during the “cold” times was 72°F and the “hot” times was 80°F.

This was Thailand, so there were not extreme temperature differences in hot versus cold seasons. That said, upon measuring 27 fatty acid indices, this study showed that one fatty acid had the most significant difference by season (aka, a p-value < 0.01). You guessed it: C15:0. Specifically, colostrum collected during the “colder” season had less C15:0 compared to the “warmer” season (mean of 0.60 and 0.75 mg/100 g, respectively). That’s 25% less C15:0 during the colder season.

That may not seem like much, but let’s move to Pariyani et al.’s study.

…to cows in Ireland.

This study also measured nutrients in colostrum, but this time from Holstein-Friesian dairy cows during spring (“cold”) vs. autumn (“warm”) in Wexford, Ireland. Unlike the Thailand study, these cows ate different diets during the year. Specifically, cows during the spring were primarily indoors and fed grass-silage. During the autumn, they were outdoors and ate pasture.

In Wexford, the lower temperatures in the spring average around 39°F, while the upper average autumn temperature is 62°F. Of the 944 small molecules they measured in this study, 15 complex lipids differed significantly between the two groups. Of these lipids, only one had levels that went down in the autumn vs. the spring: C15:0 (specifically, phosphatidylcholine C15:0). Here, C15:0 levels during the warmer autumn were 50% less than the colder spring.

A little confused? So were we.

How did one study show that C15:0 content in milk is lower during a colder season, while the other showed the opposite? The answer is likely two-fold:

• First, the Thailand study controlled for diet. No matter the temperature, the goats ate the exact same feed. This allowed them to conclude that cooler temperatures resulted in 25% less C15:0 in milk.
• Second, the Ireland study purposely tested for differences based on seasonal changes in their diet. This study showed that when cows grazed outside versus being fed grass-silage diets inside, they had 50% lower C15:0 in their milk.

In summary, both changes in temperature AND diet can significantly affect the amount of C15:0 in milk.

How what cows eat (and how long they’ve been making milk) affects the C15:0 content in milk.

Similar to the Ireland study, other researchers have reported various reasons C15:0 content can vary significantly in milk.

For example:

• When comparing corn-silage versus grass-silage diets, Shingfield et al. concluded that cows fed grass-silage diets had significantly higher C15:0 content.
• Redoy et al. showed that cows fed a low-forage diet supplemented with isobutyrate could significantly increase C15:0 content in milk. This makes sense, since butyrate helps feed ruminal microbes that make C15:0.
• Beyond what cows are eating, Sun et al. demonstrated that C15:0 content also changed based on a cow’s lactation stage. Specifically, cows that had been lactating for 22 to 100 days had significantly higher C15:0 content compared to those lactating for less than 22 days and more than 100 days.

The bottom line: Peer-reviewed studies are repeatedly showing that C15:0 content in milk can vary significantly based on season, what they’re fed and supplemented, and how long they’ve been milkin’. All that said, full-fat dairy continues to be the world’s primary dietary source of C15:0, an emerging foundational nutrient that can support healthy aging at all stages.