In my April column I focused on the principles of protein nutrition in beef cattle with an emphasis on rumen degradable and undegradable protein and on meeting the metabolizable protein needs of the animal. The reason that I focused on this topic was my experiences this past winter with producers who were having difficulty meeting the protein requirements of backgrounding calves, particularly those who fed corn silage as a roughage source. With this article I would like to explore the protein value of common feedstuffs and perhaps point you in the direction of some viable options for this fall.
First let’s compare corn versus barley whether fed as silage or grain. Corn typically averages seven to nine per cent crude protein (CP) on a dry matter (DM) basis, regardless of the form fed. As a forage source, corn silage usually provides adequate protein levels for pregnant beef cows, however, for backgrounding calves and finishing programs, diets formulated with significant levels of corn silage will be short on protein. The same holds true for diets formulated with corn grain. Relative to corn, barley grain and silage have higher levels of CP, typically ranging from 11 to 13 per cent on a DM basis. Protein from both corn and barley silage is relatively soluble in nature and thus is readily degradable in the rumen. Poor silage preservation techniques can, however, lead to heat-damaged protein which is poorly digested. It is also important to remember that while corn grain has a lower level of CP, it also has a higher rumen undegradable protein content than barley grain. This is particularly important in finishing programs. Not only will such programs be short on protein, but they may also be short on rumen degradable protein, a situation I will address below.
Legume silage (i.e. alfalfa or sweet clover) while harder to ensile, is typically superior to cereal silages in terms of CP content, averaging 16 to 18 per cent CP. Legume silage is also high in soluble protein which means that it is extensively degraded in the rumen. For backgrounding operations, alfalfa silage is an excellent protein source. In some cases, feedlot operators will layer alfalfa with their corn or barley, which helps with the ensiling of the legume and increases the overall crude protein content of the cereal silage.
Similar to silage, the protein content of typical hays will vary with forage type. Legume hay (16 to 18 per cent CP) will be higher in CP than grass hays (nine to 11 per cent), with grass/legume mixtures intermediate. It should be emphasized that these are typical values. Actual values will vary depending on a number of factors with the most important being the stage of maturity at cutting. For example, alfalfa hay cut at 10 per cent bloom might average 18 per cent CP while at full bloom, the protein content could drop to 14 per cent or less.
A number of producers rely on a variety of byproduct feeds to meet protein needs. Lentil or pea screenings are good examples. Averaging 18 to 20 per cent CP, lentil screenings work well in both backgrounding and wintering cow diets, particularly considering that their energy content is similar to that of a light oat. Grain screening pellets, depending on their formulation, are an intermediate source of both energy and protein, averaging 13 to 15 per cent CP. As has been discussed previously in this column, wheat or corn distillers grains with solubles (DDGS) at 40 and 30 per cent CP, respectively, also fall into this category. Not only are they excellent sources of CP, but they also supply rumen undegradable protein. Depending on cost, it is not uncommon to see corn or wheat DDGS in finishing diets at levels ranging from 10 to 15 per cent or higher. At levels greater than 10 per cent of the DM, DDGS are not only supplying protein, but are also used as an energy source.
One can also encounter a variety of opportunity feeds that as long as they are processed properly (i.e. cracked or rolled) can serve as excellent protein sources. Examples include cull or heat-damaged faba, pinto and kidney beans which will average 20 to 22 per cent CP. Off-grade canola seed or soybeans can also be fed to beef cattle. While excellent protein sources, one needs to keep in mind that they also supply a significant level of fat which can have an adverse effect on feed intake. In such situations, dietary fat levels should be kept below five to six per cent (DM basis). Both oilseeds need to be processed for effective utilization, particularly off-grade canola seed.
Finally let me come back to the scenario where one is feeding high levels of corn grain, perhaps in combination with corn silage. In such a situation, you not only need to balance the ration for CP, but you also need to supply a source of rumen degradable protein to ensure optimal rumen function. In this case, a commercial protein supplement that has a combination of natural protein and urea would be an excellent choice. An example would be a 32(20) supplement which has 32 per cent CP with 20 per cent of the CP coming from non-protein nitrogen (i.e. urea).
In summary, there are a lot of options available to meet the protein needs of your cattle; the key is to plan ahead.