What fats are used in dairy cows? A comprehensive guide

December 27, 2025 •

4 min read

The fat content in a typical dairy cow's diet is relatively low, around 2-3% of total dry matter, with supplemental fat often added to increase energy density for high-producing animals. Understanding what fats are used in dairy cows is crucial for optimizing milk yield, fertility, and overall health while avoiding negative effects on rumen function.

Quick Summary

This guide details the different types of fat sources, including naturally occurring fats and commercial supplements, that are strategically incorporated into a dairy cow's diet. It covers the metabolic processes involved, the specific fatty acids utilized, and the impact various fat sources have on milk production, fertility, and body condition.

Key Points

Fat is a highly concentrated energy source: The primary reason for supplementing fat is to increase the energy density of the diet for high-producing cows, particularly during the negative energy balance of early lactation.
Rumen-protected fats are key for high levels: Unlike monogastrics, cows require fat supplements that are 'protected' from the rumen environment to prevent disruption of beneficial fiber-digesting microbes.
Fatty acids have specific functions: Different fatty acids, like palmitic (C16:0), oleic (C18:1), and omega-3s, have specific metabolic effects, influencing milk fat, body condition, and fertility.
Excessive fat can be harmful: Including too much fat, especially unprotected unsaturated oils, can interfere with rumen fermentation, reduce feed intake, and depress milk fat content.
Strategic supplementation is crucial: The optimal type and amount of fat to feed depends on the cow's stage of lactation and production goals, requiring a tailored approach for maximum benefits and cost-effectiveness.

Fats, or lipids, are a critical component of a dairy cow's diet, providing a highly concentrated source of energy that is essential for maintaining high levels of milk production, especially during early lactation when a cow's energy demands are at their peak. However, ruminant digestive physiology, particularly the unique environment of the rumen, dictates how fats can be effectively and safely incorporated into the diet. The primary goal of using supplemental fats is to increase the energy density of the ration without interfering with microbial activity in the rumen.

Sources of Fat for Dairy Cattle

Dairy cows obtain fat from two main sources: the fats naturally present in feedstuffs and supplemental fats added to the diet. The composition and characteristics of these fat sources are key to their utilization by the cow.

Natural Feed Fats

Naturally occurring fats are a baseline component of a cow's diet and are found in various feedstuffs:

Forages: Contain lipids, predominantly as glycolipids, which have a high proportion of polyunsaturated fatty acids (PUFAs), such as linolenic acid (C18:3).
Grains and Oilseeds: Cereals, oilseed meals, and oilseeds like soybeans, canola, and cottonseed are significant sources of fat. The fat in these sources is mainly in the form of triglycerides rich in unsaturated fatty acids, like linoleic acid (C18:2). Excessive amounts of unprotected unsaturated fats can be detrimental to rumen microbes, which is why they are often fed in moderation.

Supplemental Fat Sources

Supplemental fats are added to increase energy density and provide specific fatty acids. These can be broadly categorized based on their effect in the rumen.

Rumen-Active Fats: These are primarily straight vegetable or marine oils (e.g., linseed oil, fish oil) that are highly unsaturated. While rich in desirable omega-3 and omega-6 fatty acids, they can disrupt rumen fermentation if fed in large quantities.
Rumen-Protected/Inert Fats: To circumvent the negative impact of unsaturated fats on rumen microbes, these fats are specially processed to resist biohydrogenation in the rumen and are digested post-ruminally. This provides a stable, concentrated energy source.
- Calcium Salts of Fatty Acids: Formed by reacting fatty acids (often from palm oil) with calcium, these supplements are protected from rumen breakdown as long as the pH remains stable. A common example is Megalac.
- Fractionated Palm Oil: These products, rich in palmitic acid (C16:0), are saturated and have high melting points, making them less reactive in the rumen. They are often sold in prilled or flaked form.
- Hydrogenated Tallow: Animal fats, such as tallow, can be hydrogenated to increase saturation, making them less prone to rumen degradation.

The Role of Key Fatty Acids

Individual fatty acids play different roles in the cow's metabolism, and targeted supplementation can influence milk composition, body condition, and fertility.

Palmitic Acid (C16:0): Increases milk fat percentage and is most effective in mid- to late-lactation to drive nutrients toward milk production.
Stearic Acid (C18:0): Produced from the biohydrogenation of unsaturated fats in the rumen, stearic acid's digestibility decreases with higher intake.
Oleic Acid (C18:1): Improves total fat digestibility and directs nutrients toward restoring body condition, making it valuable in early lactation.
Omega-3 (Linolenic Acid, C18:3) and Omega-6 (Linoleic Acid, C18:2): These polyunsaturated fatty acids are important for immune function and reproduction. Supplemental omega-3 can improve embryo survival and fertility, especially when rumen-protected.

Comparison of Different Fat Supplements


Feature	Calcium Salts of Fatty Acids	Prilled/Fractionated Saturated Fats	Unprotected Vegetable/Marine Oils
Rumen Effect	Minimal interference if pH is stable.	Very little impact; highly inert.	Can harm fiber-digesting microbes.
Primary Fatty Acid	Primarily palmitic (C16:0).	High in palmitic (C16:0), stearic (C18:0).	High in unsaturated fatty acids (oleic, linoleic, linolenic).
Main Benefit	Highly digestible energy source; increases milk fat.	Increases milk fat; supports body condition.	Provides essential fatty acids for reproduction and health.
Best Used For	General energy density boost across lactation.	Targeting increased milk fat and energy partitioning.	Strategic supplementation for fertility, must be limited.
Risk of Milk Fat Depression	Low if rumen pH is managed.	Low due to saturation.	High if fed in excess.

Understanding the Metabolism of Fat in Dairy Cows

The digestive process for fats in a cow is complex. Dietary lipids are first hydrolyzed in the rumen, releasing free fatty acids. Unsaturated fatty acids then undergo biohydrogenation by rumen microbes, converting them into more saturated forms like stearic acid. These saturated fatty acids, along with rumen-protected fats, pass into the small intestine where they are absorbed. The absorbed fatty acids are then repackaged into lipoproteins and circulate in the bloodstream. During lactation, these lipoproteins are taken up by the mammary gland for milk fat synthesis. Alternatively, they can be stored in adipose tissue during periods of positive energy balance or mobilized for energy during negative energy balance.

Conclusion

Dairy nutritionists have a variety of fat sources and supplements to utilize when formulating rations to meet a high-producing cow's energy needs. What fats are used in dairy cows depends on the desired outcome, such as increasing milk fat percentage, improving body condition, or boosting reproductive performance. By understanding the unique way a cow's rumen processes different types of fats—from naturally occurring forage lipids to specialized rumen-protected supplements—producers can make informed decisions to enhance cow health, productivity, and profitability. This strategic use of fats can mitigate energy deficits, improve milk quality, and support overall herd performance. For further reading on detailed dairy cow nutrition, refer to resources like the Extension Foundation's guides on feeding fat.

Frequently Asked Questions

Bypass fat is a type of fat supplement that is treated to 'bypass' or resist digestion in the rumen, ensuring that the fat is absorbed and utilized in the small intestine. It is used to increase the energy density of a dairy cow's diet without negatively impacting rumen function.

High-producing dairy cows, especially in early lactation, have extremely high energy demands that often exceed their energy intake, leading to a negative energy balance. Fat supplements provide a concentrated source of energy, helping to meet these demands and supporting milk production.

Yes, feeding excessive fat, particularly unprotected unsaturated fats, can be detrimental. It can overwhelm the rumen's biohydrogenation process, disrupting the microbial population, reducing fiber digestion, and leading to decreased feed intake and milk fat depression.

The effect of fats on milk fat depends on their saturation. Saturated fats, like palmitic acid, tend to increase milk fat percentage. Conversely, unprotected unsaturated fats can produce intermediate isomers in the rumen that inhibit milk fat synthesis, leading to milk fat depression.

Some fatty acids, specifically omega-3s (like linolenic acid) from sources like linseed or fish oil, are important for reproductive health. They are involved in hormone production and can improve embryo survival and fertility, particularly when fed in a rumen-protected form.

Naturally, dairy cows consume fat from forages, which contain lipids rich in unsaturated fatty acids, and from grains and oilseeds like soybeans, canola, and cottonseed, which provide triglycerides.

Yes. Unsaturated fatty acids are extensively biohydrogenated (saturated) by rumen microbes, while saturated fats largely pass through the rumen unaltered. This process is a key difference in how ruminants metabolize dietary fat compared to non-ruminants.