Huge differences exist in available protein for cattle depending on the type of forages (i.e. winter annuals, summer perennials, hay, silage etc.) they are on, types of supplements which available and so on. The requirements are likewise highly variable depending on age, production stage, breed, etc. Recent studies have shown that significant differences exist in how cattle respond not only to protein level but also type of protein when grazing a forage base that is relatively low quality in terms of protein content and nutrient digestibility.
For years, the most common question asked when scrutinizing virtually any nutrient source, be it forage or supplement was “what's the protein content?” This is still true on many operations, especially those that adhere to the “that's the way we've always done it” school of cattle production. What is protein anyway? Protein is a nutrient required for various functions in the body. What makes it unique is that it is made up of smaller components known as amino acids and that these molecules include nitrogen in their make-up. On the average, a protein molecule contains 16 percent nitrogen. A way to analyze for protein in a given feed or forage is to analyze the nitrogen content and multiply this number by 6.25. This will give you the approximate protein content of the material to be analyzed. This nitrogen inclusion is relatively unique to proteins since we do not see this characteristics in starches, fats or fibers unless they are bound to a protein in some way. What is more unique about proteins is that in the complex digestive system of the ruminant animal (cows, sheep, etc.) different proteins are digested in different areas in different ways and at different rates of speed. You can see there are lots of variable to consider. For optimum production we need to match the types of protein to the animal at it's given phase of production.
When we talk about types of protein we normally refer to crude protein, degradable protein, soluble protein and undegradable protein. Let's talk about each of these for a second. Crude
protein is a general, all-inclusive term for the protein content of a given feed or forage. It includes all the protein as determined by laboratory analysis. It also includes all of the other types of protein mentioned above. One thing that needs to be noted is that crude protein is a very general term and does not take into consideration digestibility or other factors of concern. Degradable
protein is that fraction of crude protein which is broken down in the rumen by the ruminal bacteria. As feeds and forages are fed to cattle, the first of the four stomach compartments that the material enters is called the rumen. It is basically a large (in a mature cow the rumen can have a capacity equal to a 55 gallon drum) fermentation vat. The rumen is home to countless microbes (bacteria, protozoa, fungi, etc.) and it is this microbial population which begins the early stages of the digestive process of this material. The microbes attach themselves to the feed and forage particles and begin consuming the nutrients and incorporating these nutrients into their own bodies. This is what happens with the protein in a feed or forage particle, a portion of it is consumed by the microbes - not all but a portion. This differs with different types of ingredients and forages. The portion of the protein consumed by the rumen microbes before it leaves the rumen is considered the degradable protein. You will also see this referred to as degradable intake protein (DIP), ruminally degraded protein (RDP) as well as other terms attempting to describe this process.
A portion of the degradable protein which is receiving a lot of interest lately is referred to as soluble
protein. This is the portion of the degradable protein which is broken down by the rumen microbes in a very short period of time upon entering the rumen. It is considered to be the protein fraction immediately available to the microbial population. Once again, this number varies depending on the type of forage or feed ingredient.
A question we need to address is why do the microbes need protein and why does this seem to be so important. Remember that the ruminal microbes initiate the first steps of the ruminant digestive process. If it weren't for this system, cattle and other ruminants could not utilize the large amounts of forage or some of the other high fiber materials from which they can extract nutrients. The fermentation process that takes place in the rumen by the microbial population breaks down materials that otherwise would be indigestible. In order to do this effectively and efficiently the microbes must be fed just like any other living organism and protein is one of the more important components of their diet. Secondly, as the ruminants digestive process proceeds, large volumes of partially digested material move from the rumen to the next three compartments in the ruminant's stomach system (reticulum, omasum, abomasum). As this partially digested material (digesta) moves it carries with it large numbers of these rumen microbes. These microbes are also digested by the animal and the nutrients that are incorporated into the bodies of these tiny organisms then are digested and absorbed by the animal itself. This gives rise to another protein term known as microbial
protein. This is a major protein source available to the cow which is derived from the microbes that are digested. Remember, this microbial protein is derived from soluble and degradable proteins as they enter the rumen.
Refer back a few paragraphs when we said that protein is made up of various amino acids (i.e. lysine, methionine, histidine, etc.). All organisms have a specific need for certain amounts of certain amino acids. In other words, they need a certain amount of lysine, a certain amount of methionine, etc. What this tells us is that animals do not have so much of a protein requirement as they have an amino acid requirement. This degree of understanding of amino acid nutrition has been well adopted by the swine and poultry industries. Unfortunately, due to the complexities of the ruminant digestive system, determining quantitative levels of amino acid requirements has been very difficult. The dairy industry has had some success in this area and have seen positive results in terms of milk production by modifying the amounts of specific amino acids in the diets. In the beef industry we are still “inventing the wheel” in this area although some fairly basic research has been completed with encouraging results. What we have found is that the amino acids cattle receive through the digestion of ruminal microbes is not optimum. In other words, additional amounts of certain amino acids are necessary to meet actual amino acid requirements. Research in the dairy industry has shown positive responses in milk yields to feeding of supplemental methionine, a particularly important amino acid in the diet of all organisms. Note, however, that this is under certain conditions with cattle in certain phases of production. We have a long way to go to truly understand all the nutritional biochemistry involved in this process. Many feeds and forages have low values for certain amino acids. More accurately, we might say that on rations or diets containing substantial amounts of certain ingredients or forages, the ruminal microbes produce low amounts of certain required amino acids. That's a complicated way of saying that when cattle eat certain feeds or forages; they do not get what they need. This is especially true of the forages. Feeding of hays and grasses such as bermudagrass, fescue, bahiagrass, sorghum-sudan grasses, etc. result in substantially less than optimal essential amino acid production. This is also true of other forages such as alfalfa, corn silage, etc. Forages such as fresh wheat pasture, ryegrass, oats, etc. used as winter pastures are very high in their degradable and soluble protein contents. As we learn more about this area we will learn to manipulate the cow's diet to result in the optimum level and profile of amino acids (proteins) flowing into the intestinal tract and therefore available to the cow itself.
At this time, a way we can have an effect on the amino acids received by the cow is by the feeding of by-pass
protein. This is a common term in the cattle industry but you will also hear it referred to as undegraded intake protein (UIP), ruminally undegraded protein (RUP), escape protein or a number of other terms used to describe protein which is not broken down by the microbes in the rumen and are available to the cow more or less “intact.” Sometimes in ruminant nutrition we can get bogged down by the various terminology used to describe the same thing Understand that virtually all feeds and forages have a certain amount of their protein that passes through the rumen undegraded. The difference is that some feed ingredients possess protein which is predominantly undegraded while other ingredients contain protein that is predominantly degraded in the rumen. For example, protein meals such as fishmeal, bloodmeal, corn gluten meal and feathermeal contain higher levels of by-pass protein, in other words, more of the protein from these sources reach the intestinal tract intact. Other proteins, such as cottonseed meal or soybean meal are higher in degradable protein meaning a higher percentage of the protein is broken down in the rumen by the microbes and is transformed into microbial protein as discussed earlier. Urea, which is commonly used as a protein source is entirely degradable and is entirely soluble for that manner, meaning that it is rapidly broken down in the rumen and utilized by ruminal microbes. Urea can be very effectively fed as a source of protein if fed correctly. We have covered this subject on more than one occasion in this magazine.
In situations where cattle are consuming high levels of degradable and soluble protein sources (i.e. cattle on winter pasture) we can improve performance by supplementing with a by-pass protein source of some type. By doing this, what we effectively do is improve the profile of amino acids which ultimately reach the small intestine and can be absorbed directly by the cow.
Virtually any type of forage base can possess less than desirable nutritional characteristics. It may be pasture that has grown tall and rank, is unfertilized or late in the growing season when accumulation of high levels of acid detergent fiber (ADF) and neutral detergent fiber (NDF) create forages that are poorly digested. Other circumstances which create this type of roughage include hay that is unfertilized, improperly fertilized or was not harvested in a timely fashion (quality was sacrificed for quantity). Possibly the species of grass grown as hay is simply not a great nutrient source. Obviously, some grasses are naturally lower in protein and higher in fiber components making them less digestible, regardless of how they are fertilized and managed. In situations such as these, when these roughages are fed alone, as this material is consumed and enters the rumen, the microbial population has it's work cut out for it. Initially, with a roughage source possessing a low digestibility, the bacteria are having to work doubly hard to break down these particles to extract any nutrients for their own needs. Since the amount of nutrient available is lower to begin with and it takes longer and more effort to get to it, the microbes cannot grow and multiply as fast as is optimally necessary. In other words, the initial digestive process slows down. This means that forage particles must spend more time in the rumen to be fermented to a given endpoint. Secondly, at this point the amount of nutrient released is lower so what we have is a double edged sword. Not only is there not as much protein, energy, minerals, etc. available to begin with, what's there takes longer to get and limits how much the cow can eat in a given period of time. So in two ways this reduces her opportunity to potentially consume the nutrients she needs.
So how do we solve this? As discussed above, if we know how much protein and other nutrient is in a given forage source we have a much better idea where our shortages lie and what we need to do. First, we have to “crank up” the microbial population in the rumen. In many cases this simply means increasing the protein intake but more specifically we need to increase the intake of degradable and especially soluble protein. In other words, we need to provide more of the specific protein components the microbial population needs to grow and reproduce. By increasing microbial numbers and their activity, more poorer quality forage can be fermented and in a more extensive manner and helps solve the two problems described above. This can be accomplished by feeding or supplementing with cottonseed meal, soybean meal, whole cottonseed, corn gluten feed, alfalfa, etc., feeds and forages which are higher in degradable and soluble protein. In a case like this a small amount of urea can be especially helpful since it is considered to be 100 percent soluble protein. However, when feeding urea to meet this soluble protein need we also have to provide a soluble source of carbohydrates (starch) for the microbes to effectively use the urea and convert it to protein. Urea can be effectively fed with ground corn, milo, molasses or other sources of readily fermentable carbohydrates to meet this soluble protein need. Be aware, however, urea is not effective in meeting all the protein needs and can potentially cause many problems including sickness and death in cattle if this is attempted. Urea should make up no more than 1/3 of the supplemented protein source.
As you can see from the text so far 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. In part two of this series we will continue this discussion and examine protein levels in depth as well as how proteins are subdivided into different components.
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 firstname.lastname@example.org.