TRENDING TOPIC ARTICLE: FEED & NUTRITION Published: November 1, 2010 print issue of Progressive Dairyman In this past article, nutritionist John Hibma outlined the different forms of fats available and each of their functions in dairy rations. to jump to the article. Because this article was so popular, we asked Hibma, “Why are dairy producers curious about this topic?” Hibma says, “I suspect that many dairy farmers are realizing the critical importance of body condition in their cows and how it affects milk production throughout the lactation. "The rumen-protected fats will maintain body condition very well. The other factor is that energy balance is critical for reproduction, and a herd of cows that is long in days in milk is a herd that is losing money ... so there again, the fats do a good job of improving reproduction performance in a herd.”


As dairy farmers strive to increase the efficiency of their feeding programs, one important area of nutrition to focus on is that of fats. It is well known that fats contain about 2 ¼ times more energy than other carbohydrates.

Even though they can provide a quick fix for a diet that’s deficient in energy, fats – when used incorrectly – will negatively affect rumen fermentation, depressing both dry matter intakes and milk components.

More attention has been paid to fats in recent years as researchers understand the differences between various fats and how they affect the rumen.

Fats (technically known as fatty acids) come to us in couple of different forms – unsaturated and saturated. Then to complicate matters, there are trans-fats and conjugated fats, but those are beyond the scope of this article.


Unsaturated fats tend to be those that are in the liquid form due to their molecular makeup and include the common vegetable oils of soybean, canola and corn.

Commodity byproducts such as hominy and distillers grains also have high levels of unsaturated fats. It is the unsaturated fats that disrupt the fermentation in the rumen, more often than not leading to microbial inefficiencies and butterfat depression.

Two exceptions to the use of unsaturated fats in a dairy cow diet are the use of whole cottonseeds and roasted soybeans. Because of the physical structure of cottonseeds, the fat is released in the rumen much more slowly.

The fat in heat-treated soybeans is chemically bound such that it is also slowly released in the rumen. The rumen microbes are not overwhelmed by the fats from oil seeds as opposed to the liquid vegetable fats, which should be limited and preferably avoided in dairy diets.

Saturated fat for dairy diets is essentially limited to tallow – an animal byproduct. Because of their molecular structure, saturated fats have little or no effect on rumen fermentation.

Saturated fats essentially pass through the rumen and onto the small intestine. However, it is now known that saturated fats are not digested as well as unsaturated fats in the small intestine. So the conundrum that ruminant scientists find themselves in is how to get more unsaturated fats past the rumen and into the small intestine where they are better metabolized.

It’s been well known for many years that energy is most often the limiting nutrient in a dairy cow diet and fats provide a boost in dietary energy for dairy cows – especially high-producing cows.

During the postpartum transition period when a cow is usually in a negative energy balance, adding fat to the diet can quickly supply calories. Also in diets that incorporate a lot of hay and grass forages, fat in the ration is almost a necessity to meet higher milk production levels.

Having adequate energy in a diet is also known to affect milk protein levels, even though there are many other factors involved. For many years the challenge for nutritionists has been preventing butterfat depression when excessive levels of “rumen-active” unsaturated fats are included in a ration.

One of the more significant advances in ruminant nutrition has been the development of rumen-protected fats – also known as rumen-inert fats. The intention of these products is to allow more unsaturated fats (the ones we want) to bypass the rumen and be absorbed as energy for a cow’s metabolic and milk production needs.

Rumen-inert fats are commercially manufactured products and are marketed in one of three forms: 1) calcium salts of fatty acids; 2) prilled fatty acids; 3) hydrogenated fats (fats that have been chemically saturated). Each has a different proportion of individual fatty acids and the effectiveness of any of these products can be influenced by the selection of feedstuffs in the rest of the ration.

The inclusion of fats in a dairy diet can be approached in a couple of different ways:

1) A diet may be deficient of energy and other common feedstuffs simply do not supply that necessary energy. Oftentimes a diet is maxed-out with starch, so corn or other high-starch feedstuffs cannot be increased – even though they are excellent sources of energy. Because overfeeding of grains can cause ruminal acidosis, rumen-inert fats offer an alternative means of providing metabolizable energy to a cow.

2) As dairy farmers and nutritionists attempt to improve the feed efficiencies of dairy diets – lower the amount of feed consumed relative to the amount of milk produced – rumen-inert fats can offer an alternative to other standard feedstuffs. It must be remembered, though, that rumen bypass fats are absorbed in the small intestine and do not contribute to rumen microbial growth and fermentation. Dairy diets still must include carbohydrates such as cellulose, starch and sugars for the rumen microbes.

Rumen bypass fat has also shown promise in improving reproductive performance in dairy cows. Most fresh cows will find themselves in a negative energy balance for a number of weeks before and after freshening.

Close-up cows that are energy-deficient often develop poor ovarian follicles. The eggs in those follicles are the ones that will be presented for fertilization a couple of months later.

The feeding of rumen bypass fats has shown very positive signs of improving conception rates both because of improved follicular health at the time of ovulation and also because the cow has achieved a positive energy balance more quickly after freshening.

Specific blends of essential fatty acids are fed to cows to aid in conception. Essential fatty acids are those fats that are required for certain functions in a cow but are not made in large enough quantities in her body. Therefore, they must be supplied through the diet.

The inclusion of rumen-protected fats in dairy diets is not just about adding calories, anymore. They improve the overall health of a cow during crucial periods of transition and lactation, which will enhance the dairy’s bottom line through improved reproduction, as well as milk production. Work closely with your nutritionist or feed company professional when including bypass fats in a ration. PD


Because over-feeding of grains can cause ruminal acidosis, rumen-inert fats offer an alternative means of providing metabolizable energy to a cow. Photo by PD staff.

John Hibma