Nutritionists and dairy specialists at Provimi North America started using a new bulk tank test to troubleshoot herds that have low milk fat. The technology being used is the analysis of milk fatty acids in bulk tank samples and was developed in a collaborative work between Cornell University and Miner Institute. Combined with other technologies such as analysis of fatty acids in feeds, the fatty acids in milk can help suggest adjustments to the ration and herd management.

Isn’t Fat Just Fat? 

“The short answer? No, not all fat is the same,” says Michel Baldin, PhD, dairy nutritionist with Provimi. “Feeds will have different amounts of C16:0, C18:0, C18:1, C18:2, and C18:3. These 5 fatty acids make up 85-90 percent of total fatty acids in most dairy feeds.”

“Corn-derived products are very rich in C18:2 whereas forages and seeds like flax, are richer in C18:3. Commercially available fat supplements may contain only one fatty acid, like enriched palmitic acid supplements, but are normally blends of C16:0, C18:0, and C18:1.” 

Feeds also differ in their fatty acid availability to rumen microbes. Fatty acids in corn silage, high moisture corn, distillers, and vegetable oils are readily available; whereas fatty acids in extruded and roasted grains, and calcium-salts are somewhat protected against microbial biohydrogenation.

Fatty Acids, Milk Production and Components

Fatty acids are important components of lactating cows’ diets and are present in almost all feed ingredients. Forages have low concentration whereas oilseeds and animal fats are rich in fatty acids. 

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With regard to milk production, fatty acids can be oxidized and used by the cow to meet her energy demands for lactation. As for milk components, fatty acids are important for milk fat yield because 45-60 percent of total fatty acids in milk fat come from diet or body fat mobilization. Some fatty acids, like palmitic acid, have been demonstrated to increase milk fat yield, while others (mainly bioactive trans fatty acids originated in the rumen) can inhibit milk fat synthesis.

What Do Milk Fatty Acids Tell Us?

Milk fatty acids indicate whether or not things are going well in the rumen. They also indicate how well the mammary gland is doing at synthesizing milk components. Trying to look at milk fatty acids individually can be overwhelming, instead we started looking at fatty acid groups (de novo, preformed, and mixed). 

The de novo fatty acids have 4-16 carbons, represent 18-30 percent of total fatty acids, and are synthesized by the mammary gland using primarily acetate. Preformed fatty acids have 16-24 carbons, represent 30-45 percent of total, and come from the diet and mobilization of adipose tissue. Mixed fatty acids have 16 carbons, represent 35-40 percent, and originate half from each source.

“We can look at the contribution of each fatty acid group relative to total milk fat to identify where milk fatty acids are coming from. If contribution of de novo fatty acids is low, this could indicate inhibition of synthesis at the mammary gland or in some cases a shortage of precursors for fatty acid synthesis, says Baldin. “Low contribution from preformed fatty acids may indicate that cows no longer have body fat to mobilize, which indicates an opportunity to feed rumen inert fat supplements.”

To be able to discern the causes of low milk fat we need to look at other factors such as the contribution of each fatty acid group per 100 g of milk and the ratio trans-10/trans-11 C18:1. In this case, if the contributions of de novo and mixed fatty acids are low, but preformed is okay, the ratio t10/t11 is normal, and milk protein is good, this would suggest a need to improve fiber digestion and an opportunity to supplement palmitic acid. If the contribution of de novo and mixed fatty acids are low and the ratio t10/t11 is inverted, this would indicate milk fat depression and a need to fix rumen biohydrogenation.

Analyzing Fatty Acids in Feeds and Milk

Provimi recommends analyzing fatty acids in corn silage, distillers, high moisture corn, and by-products high in fat. We recommend checking with your preferred forage lab if they have a package that reports total fat (or ether extract), total fatty acids, and concentrations of C18:1, C18:2, C18:3 in these samples. 

Bulk tank milk fatty acid analysis can be used to troubleshoot and monitor herds with low milk fat. Recently, an innovative technique has been used for this analysis. The work of Dr. Dave Barbano (Cornell University) and Heather Dann (Miner Institute) has shown that mid-infrared spectroscopy (MIR) can be used to analyze the fatty acid groups in milk Dr. Barbano’s webinar. This is important because the MIR requires no sample preparation and already is an equipment present in many DHIA labs. We expect some DHIA labs around the country to start offering milk fatty acid analysis in the near future.

Changing the Nutrition Game 

Most commonly used ration balancing programs should have the capability to formulate diets on a fatty acids basis. Also, milk fatty acids targets started to become more available to help monitor bulk tank milk fat and protein in Holstein herds. “By looking at milk fatty acids, we can suggest adjustments to the ration and herd management”, says Baldin.  

Knowing the fatty acid profile of feeds, their impact on rumen fermentation and mammary gland performance, as well as linking milk fatty acids to ration balancing and herd management, is another piece of knowledge that dairy farmers and nutritionists could benefit from adding to the toolbox.