How Do I Supplement My Cows?

By Dr. John Comerford

This is the time of year I get the calls from beef producers that usually sound something like, "I am feeding grass hay to my cows, so what should I supplement them with?" I guess if there was an easy answer we would not need to write this column, but the answer is not easy.

All hay is not created equal

If I go back through numerous hay samples I have seen on my desk from "grass hay," it is clear there is significant variation in the feed values for hay named "grass." There can be as much as a 50 percent variation for both energy and protein values in these samples. Another significant value is moisture content. While dry hay normally has a smaller range of dry matter value, consider a 5 percent difference in dry matter for an 800-pound bale of hay. For a cow eating 20 pounds of hay, there will be 5 percent less protein and 5 percent less energy in every bite she takes in the wetter bale. Finally, the whole bale is not feed, even when it is stored inside. Weathering of a bale uses up nearly all the energy and most of the protein in a bale. Dry matter losses are generally 20 to 30 percent for bales stored outside and 4 percent for those stored inside. Table 1 shows some nutritional values observed from "grass hay."

How much hay do they eat

It does not matter how much hay you put in front of a cow. The only thing that counts is how much of it she eats and how much of it is lost. Feeder design will change that value significantly. Most studies show the typical ring feeder will result in about an 8 percent loss, the inverted cone feeder will have about a 2 percent loss, and no feeder at all can result in losses up to 50 percent. The variation in bale weight can fool the feeder. The difference in the amount of feed that is offered in a 700-pound bale is about 12 percent less than that offered in an 800-pound bale. This may make little difference to the feeder who just provides more hay when the feeder is empty, but for winter feed planning purposes, when buying hay, or when hay may be in short supply, it can be significant.

All cows are not created equal

Cows do not "read the book" very well about how they are supposed to perform. In all cases, observing cows, how they are eating, and what they look like will be the most valuable management. The amount of feed a cow eats - and the basic amount of feed a cow needs - is based on the cow's weight. The weight determines the metabolic body weight, which is the amount of feed nutrients it takes to keep a cow breathing and her organs operating. Cold weather, walking, gestation, her age and all other variations to her environment add additional nutrients to her needs, so it can be seen "the book" is not always going to be the best description of what a cow needs.

The most important feature of winter feeding cows is their condition. We know without question the most important feature of profitability in a cow herd is weaning a live calf. The condition of a cow during the winter has a significant effect on her ability to wean a calf the next year. For example, the 3-year-old cow that just weaned her first calf is eating hay this winter that is about 10 percent short on energy for her needs. She goes from a condition score of 5 to just barely a 4 by March. This cow typically has a 30 percent chance of not getting bred for the third calf, and the milk production for her second calf will be diminished. In this day of record prices for feeder cattle, the losses are costly.


The results in Table 2 highlight the type of supplementation usually needed in a cow herd. For mature cows, protein will seldom be the deficient nutrient, while energy often will be needed. Younger cows (2 to 3 years old) will have a protein requirement that is 15 to 20 percent higher.

Energy can be supplied in a number of ways. Generally the cheapest source of energy is corn. With a typical NEm (net energy for maintenance) value of 98 Mcal/cwt (megacalories per hundred weight), the deficiency found with grass hay #4 (Table 2) can be solved with about 7 pounds of corn per head daily. Any cereal grain or grain byproduct can be used to provide energy, but some processing (such as with wheat) may be needed. Food byproducts such as chips, chocolate and bakery waste are also good sources. When corn is $7 per bushel, the cost per pound is 12 cents or 87 cents per day to supplement grass hay #4. The energy value of any substitute for corn must be known to get an equivalent price. For example, oats may cost $3.50 per bushel, but supply only 83 percent of the energy of corn. The equivalent price for oats in this case would be 93 cents per day. The most expensive supplements are usually the most convenient. Blocks and lick tanks are designed for protein supplements, so the energy the cattle get from the molasses is at a high cost.

Dr. John Comerford is associate professor of dairy and animal science at the Pennsylvania State University.