The Skinny on Fat

By John Hibma

Photo by mensatic/

The subject of fat makes for an interesting topic. In human nutrition, fat is associated with poor health and obesity. As we all know, the excessive consumption of calories in the form of fats or carbohydrates has resulted in an obesity epidemic in the human population, and we have become obsessed with managing fat in our diets.

Even though it has been the singular whipping boy for nearly all of the nutritional woes of humans for the past several decades, fat does serve important functions in our overall health and nutrition. Dietary fat intake fills two needs. Fat provides a dense source of calories, and when it's deposited and stored in a body, is a potential reservoir of calories. Fat is also necessary for important biological activities in our bodies such as vitamin absorption. Our bodies require a certain amount of fat to function properly, and it generally tastes good too.

In dairy cow diets, fat provides a means toward an economic end. In properly formulated diets, fat will improve overall cow health, body condition, reproduction and milk production. Fats offer an efficient way to increase energy levels in diets for high-producing cows. And, just as it does in humans, fat can be used to increase or maintain weight on cows and heifers during both cold and hot weather. No other feedstuff can match the available calories per pound that fat does.

The challenge faced by ruminant nutritionists in adding fats to a diet is that the cow's rumen can handle only small amounts of fat at a time. Fat in the form of oil and tallow will quickly interfere with microbial fermentation of fiber, which is the primary source of metabolizable energy for cows. Similar to humans, cows must absorb fat in the small intestine. In order for this to occur effectively in dairy cow diets, the fat must be fed in a protected form that will bypass the rumen and not interfere with microbial fermentation.

In situations where only poor-quality forage is available and dry matter intakes are at the maximum, fat can quickly reverse an energy-deficient situation. In diets that are already high in grain and starch levels, fat is often the only product that can increase dietary energy. Adding more starch to a ration can cause rumen acidosis. Rumen-protected fat will not lower the pH level in the rumen.

Photo by Daniel Bouwmeester/

The ideal diet for all dairy cows should be comprised of 50 to 60 percent forages. In the Northeast that usually means corn silage, grass haylage or hay. And while high-quality corn silage can provide a lot of dietary energy, corn silage does not have enough protein to support high levels of milk production. Hay crop forages may have higher protein levels, but they don't have enough calories. There's usually a trade-off of protein for calories in most feedstuffs.

The decision to use supplemental fat in dairy cow diets should first and foremost be based on the levels of milk production you expect from your cows. There's a pretty good dividing line for Holstein cows around 100 pounds of milk production. To get those cows to peak at higher than 100 pounds of milk and sustain that production for a couple of months, the diets will need supplemental fat to get the energy in the ration up where it needs to be for that production.

Looking at it just a little bit differently, if you expect a daily milk average of 70 pounds per cow or more, you generally need about 10 to 15 percent of your cows providing over 100 pounds of milk at any given time. Not having added fat in the diet will almost always keep the herd average below 70 pounds of milk. Most high-corn-silage diets can only supply enough calories to get cows up into the high 90s area, and production quickly falls off because the diet is energy-limiting and can't provide any more calories for additional milk production. Eventually their bodies will divert energy to maintenance needs rather than milk production.In the summertime heat, added fat will help keep energy levels up when dry matter intakes drop. When cows start getting too ribby, it's time for some supplemental fat in the diet.

Nearly every dairy cow experiences a negative energy balance at the time of freshening. This is where adding fat to the diet really pays off. Bypass fat in both the close-up ration and the fresh cow ration keeps body condition on the cow when she needs it most. Study after study has shown that a positive energy status in both close-up cows and fresh cows has a significant influence on maintaining proper immune function at the time when those cows are under the highest levels of stress of their lactations.

There's also a lot of evidence confirming the value of bypass fats contributing to improved conception in high-producing cows. Certain long-chain fatty acids are necessary for proper formation of follicles, hormone secretions and ovulation. Providing them through properly formulated bypass fats will help get cows pregnant in a timely manner.

Fat is made up of a multitude of fatty acids that are bound together. It's the variety and amounts of these fatty acids that give fats their unique characteristics. Fats that are in liquid form, such as corn and canola oil, have different types of fatty acids than butter or tallow. The fatty acids used in rumen bypass supplements today have been carefully selected for their influence on meeting metabolizable energy requirements as well as their influence on improving butterfat and protein levels in milk.

Milk cows are genetically capable of making significantly more milk than they did 50 years ago. Along with that, the economics for many dairy farmers today require that cows be producing over 22,000 pounds of milk annually if they hope to stay in business. Feeding efficiencies and nutrient densities must be optimal, and every mouthful of feed a cow consumes must count. High-producing cows consuming an energy-packed diet with the correct added fat will produce more milk and breed back sooner while maintaining body condition and good health. It all helps with the bottom line.

The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.