Cattle Today

Cattle Today



by: Stephen B. Blezinger

Part 2

A while back we reviewed protein nutrition in cattle and discussed at length individual protein components. The following is the second part of this series and is well-timed given the AI and Herd Bull topic for this issue. Protein is an extremely important part of the breeding program for both cows and bulls. Artificial Insemination programs require feeding programs properly balanced for all nutrients with protein and protein components a very major part of this. The following discussion considers a variety of issues as related to protein nutrition in these breeding cattle.

In the previous discussion of protein in cattle, we discussed crude and degradable protein (protein that is available to the rumen bacteria and is readily broken down in the rumen). These forms of protein make up a very large portion of the animal's total protein intake and sources include soybean meal, cottonseed meal, corn gluten feed, whole cottonseed, urea (protein equivalent).

Other sources of protein include corn gluten meal, distillers grains, brewers grains, blood meal, feather meal and fishmeal. These sources are not as well broken down in the rumen and are considered higher in by-pass or un-degraded protein and will therefore not provide protein components to the microbial population as effectively. These sources should be used once the degradable and soluble protein demands. Use of by-pass protein sources is helpful in improving the overall quality of the protein or rather amino acids that reach the small intestine and are actually absorbed by the animal. As we discussed in the last issue, the protein the cow extracts from the digestion of rumen microbes is pretty constant assuming degradable and soluble protein needs are met but that this protein source may not provide adequate levels of certain amino acids, especially in high producing cattle, growing cattle and cattle that are stressed. In situations where cows are placed in an embryo transfer program, embryo yield and viability has been improved through the appropriate feeding of certain by-pass protein sources which improve the levels of certain amino acids consumed by the cow. This has also been shown to be true in the dairy industry in terms of increasing milk production and improving butterfat content.

The use of by-pass protein sources is also appropriate during the feeding of certain forage sources which, unlike the situation described above, are actually quite high in protein. In cattle consuming winter annuals such as wheat, rye, oats, ryegrass, etc., intake of soluble protein tends to be very high. These forages can possess very high protein contents. Data collected on these types of forages has shown dry matter protein to exceed 30 percent. While this is good in terms of general crude protein needs, a very high proportion of this is soluble protein, meaning it is going to be fermented and utilized by the microbes and be used to produce microbial protein as described above. Also, in these situations, because the soluble protein is so high, in many cases the microbes cannot utilize all the protein available and much of it can actually pass through the cow unused. In addition to this, since the moisture levels in these roughages is so high the rate of speed with which the digested material passes through the tract is very high, reducing the time in which the animal has an opportunity to further digest and absorb nutrients from this source. Several steps can be taken to help offset this problem. First, to help slow down the “rate of passage” or how fast this forage material passes through the cow, always provide access to at least some dry hay. This will provide some drier and bulkier material to slow the movement. Second, feed a small amount of a grain source to provide carbohydrates to the rumen. In order for the microbes to effectively use the soluble protein that is available during the digestive process, they must have access to some carbohydrates (starch) with which to combine the nitrogen extracted from the protein in order to reform these components into bacterial protein. Finally, providing a small amount of by-pass protein sources such as those discussed above will help meet those amino acid needs not met by bacterial protein. This is especially helpful in cows you are preparing for breeding, growing calves or stressed cattle.

Gaining a better understanding of protein nutrition can go a long way to making your herd more profitable and productive reproductively. Although we cannot focus on protein intake and intake of subsequent protein components alone, it does make up a large and very important part of the overall nutritional program. It also tends to be a very expensive portion of the nutritional program. Understanding protein levels and types in your forages and how to compensate for shortages or excessive levels can improve performance, production and efficiency greatly and can, most significantly, increase your profits.

The term or measurement of crude protein is actually broken down into three protein fractions known as degradable, soluble and by-pass protein. The following diagram can help you better visualize how these protein components exist and how they are degraded or broken down in the cow.

As you can also see by this chart a certain portion of the undegraded or by-pass protein is totally unavailable to the cow. It may be bound up in the acid detergent fraction of the fiber, or may have been heat damaged in the harvest and storage process or during the manufacturing/milling process common to some feeds.

Table 1 and 2 provides some numbers of actual dry matter crude protein contents as well as the portion of these protein sources that are soluble, degradable, undegradable and bound.

All values are on a dry matter basis.

Let's discuss these charts just a bit to help you understand the numbers that are found there. Take cottonseed meal for instance. On a dry matter basis, cottonseed meal (CSM) is approximately 43.6 percent crude protein. Of this crude protein content, 22.0 percent is soluble or about 9.6 percent of dry matter crude protein (43.6 percent X 22 percent = 9.6 percent). This means that this amount of protein from cottonseed meal is rapidly degradable. Only 41 percent of the total crude protein or 17.88 percent of dry matter crude protein (43.6 percent X 41 percent) is undegradable or by-pass protein. Very little (2.7 percent) of the protein is actually bound and unavailable to the cow. In comparison look at corn gluten meal, it is 68.9 percent protein on a dry matter basis with 55.0 percent of this protein being undegradable.

How does one apply this? While we really do not have what most nutritionist consider good estimates of what beef cattle require in terms of soluble, degradable or undegradable protein we can “interpolate” a lot of this from work done in the dairy industry. Remember that dairy research has a lot of value to us as beef producers because we are basically attempting to do the same thing: get cattle bred and turn feed and forage into milk. A typical dairy cow ideally requires protein components at about the following levels: soluble protein - 31.0%; degradable protein - 61.0%; undegraded or by-pass protein - 39%. These numbers would hold fairly consistently for a heavy milking beef cow. The primary difference is that a mature beef animal will not require as much total protein as a dairy cow will but the proportion of these components is fairly accurate.

At this time of the year when winter pastures are being grazed or early spring growth is available, these forages are characterized by high moisture contents and high levels of soluble protein, much higher than what is required. Since the overall protein content of these pastures is so high (25 to 30 percent protein on a dry matter basis) typically, feeding a few pounds of grain will balance the energy needs and a grain such as cracked corn or hominy is also high in undegraded or by-pass protein, helping the protein components somewhat. Conversely, when feeding a grass hay, especially hay that may have been allowed to get a little more mature than is preferable, feeding of a protein source such as cottonseed or soybean meal will prove beneficial. As you can see, grass hays tend to have protein which is less degradable than other forage sources. As it matures or when it is cut later in the season, this level of degradable protein goes up even more. Under appropriate circumstances even the use of urea is applicable when properly managed.

Attention to these protein components is especially important with cows capable of producing high volumes of milk, young, rapidly growing cattle and cattle in special production programs such as A.I. or embryo transfer programs. Cattle you are preparing for breeding will also benefit from not only balancing their crude protein needs but from balancing protein component levels as well.

Crude protein content of a forage, ingredient or feed is obviously very important. But as this information shows, as have the previous parts of this series, there is a lot more to protein than meets the eye. Familiarize yourself with the numbers above and begin taking into account how your supplements may need to be changed from time to time in order to compensate for variances in these components. Your herd's performance and efficiency will benefit greatly.


As mentioned in the previous part of this series, as you can see from the text that protein nutrition in ruminants is quite complex – much more than just “what's the protein in that range cube?” Proper protein feeding is very important for growth and a multitude of functions related to health, reproduction, milk production and so on.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX 75482. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at For more information please visit


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