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RUMEN FUNCTION IN BEEF CATTLE - PART 4

Steve Blezinger
Ph.D.

In this final part of our series on the rumen development, function and mechanics we need to spend some time on how we can move cattle from one type of diet or feeding system to another. We also need to look at ways that we can manipulate, or actually improve rumen function in cattle to increase performance.

In the overall beef production system, it is very common to change beef cattle from one type of feeding program to another. Generally this is done as standard operating procedure as is the case when we take growing cattle from the ranch to the stocker phase and onto the feedlot. Other situations which are similar is that in placing cattle on feed for show and we must increase energy intake to increase gains. Yet another circumstance occurs when we encounter drought conditions and we run very short on forages to feed the herd and we must resort to feeding a more grain based ration. In each of these situations, in order to avoid serious physiological and metabolic complications we have to “adapt” the cow and the rumen to this different ration.

Performing this properly is simply a matter of a) understanding how the rumen works, and b) knowing the energy levels of various feed ingredients.

A Little Review

Over the last few weeks we've discussed how the rumen works at length. Let's review a couple of things.

First, remember that under normal circumstances the cow derives her nutrients from a predominantly foraged based feeding system. In other words grass and hay which are high in fiber and relatively low in soluble carbohydrates or starch. A good quality forage program is considered by many to be the “ideal” feeding program for cattle since a cow is designed to handle and process large amounts of this type of feed material. As a cow eats this fibrous material the rumen pH is relatively high (6.0 to 6.5) and the system works without many difficulties.

As we begin adding grain to the diet (corn, milo, oats, barley, etc.), the amount of starch entering the rumen increases. This starch is broken down rapidly by the rumen microbes and produces increasing amounts of organic acids. This increased acid production reduces rumen pH making it more acidic. If the acid level gets too high (this makes the rumen pH too low) we can get into a number of metabolic and health problems. This is why we must be careful.

Adapting to Feedlot Rations

Since most feedlot-type diets are very low in fiber (5 to 10 percent) we have to adapt cattle to these rations over a period of time. Commonly you will see a feedyard make this change over a three to four week minimum time period and utilize four to five different rations, each being higher in energy and lower in fiber than the previous ration. Since this can be done in many different ways using many different ingredients the illustration that follows will be relatively simple. Understand that this is only one of many ways this can be implemented and the number of ingredient combinations that can be used is almost unlimited.

Stage 1

Generally, as cattle are moved into the feedlot and onto a higher energy ration they are coming from a pasture situation where they have been consuming mainly grass and/or hay. This is not as true as it one was since preconditioning is becoming a trend if not a necessity. We are finding that cattle perform better if, between the ranch and the feedlot, they are preconditioned and trained to eat a ration which has more grain. It also teaches them to eat from a feed bunk or trough instead of grazing. For this purpose, however, we'll assume these cattle are coming straight off pasture.

As cattle are placed in pen in a feedyard they are given some type of grass hay as well as the starter ration (Table 2, column A). In many cases the starter is top-dressed (spread over the top) of the hay so that the cattle must eat through the feed in order to get to the hay. In many cases cattle have never been in a pen before and eating from a feed bunk or drinking from a waterer is totally foreign to them. They are, however, more than likely familiar with consuming some type of hay and will be drawn to it. By top-dressing with the starter feed they become accustomed to the smell and taste of the feed as they get to the hay. The starter feed itself, in most cases is highly palatable and is somewhat more nutrient dense than the subsequent feeds. This is necessary because for the first few days cattle may not eat very well and each mouthful has to give them as much nutrient as possible to get them back on track after the transition stress. In many cases, these starters may include a medication such as chlortetracycline to help deal with potential systemic infections.

The starter feed is also fairly high in fiber. It is higher in energy than what cattle have been accustomed to on pasture, but is not so high that it should cause a digestive upset in cattle. Starter feeds are normally provided over a period of five to seven days. In some cases it may be a bit longer if cattle are having difficulty adapting and getting started on feed. This starts the process and begins adapting the rumen to the higher grain, starch and energy intake. It begins reducing the number of microbes in the rumen which are necessary to digest fiber and increases the numbers needed to digest the starch.

Stage 2

After the five to seven day stating period, cattle are switched over to the second ration (Table 2, Column B). You may see the terminology used for these different rations as Stage 2, Step-up 2, Grower 1 or something similar. Examples of these are provided in Table 1. This second ration will be somewhat lower in fiber than the starter and therefore higher in grain and energy. A good rule of thumb is that each step-up ration is about 10 percent higher in energy than the previous ration. Since in the feedlot we are attempting, in many cases, to maximize intake, we want cattle to be increasing the amount of each ration they consume to be increasing every day. As we step from one ration to another, however, it is common to see intake back off just a bit as they move up to the next ration. The main reason for this appears to be a link between energy intake and how it relates to overall dry matter intake. As we increase the amount of energy provided, the system must adapt to the higher level of energy and will typically drop back a bit for a couple of days as the system attempts to keep energy intake about equal to what it has been. After this adaptation occurs then the increase in intake will resume and more energy is consumed.

Once again, cattle stay on this second ration about five to seven days before moving onto the next stage of the ration program. (Table 1)

Stage 3

The third ration (Stage 3, Step-up 3, Grower 2) Follows the same principle as the previous ration, increasing grain, reducing fiber and ultimately increasing the energy density, once again, moving to more of a grain based ration and away from one which is forage based. Occasionally you will find a feeding program that includes a fourth set but these are not extremely common and is probably unnecessary. As before, cattle remain on this ration five to seven days.

Finishing Stage

The final or finishing stage takes the animal to the point where we have reached the maximum grain level and minimum fiber level. A number of programs actually exist where they remove the fiber altogether but this concept has never been one that I have been very comfortable with. In cattle on a high grain or finishing diet you see several occurrences. These may include:

·Reduced rumen pH due to increased acid production

·Reduced rumination, i.e. cud chewing. Remember this is a mechanism to increase mechanical fiber digestion. Since fiber levels are low, little cud-chewing is necessary.

·Increased licking of the hair coat. Some researchers feel this is related to the lower fiber content of the ration and the animals natural desire for fiber in the ration. Along with this comes increased amount of hair in the rumen and increased hair penetrating the rumen wall. This can be a potential pathway for microbes to enter the animal's blood stream.

·Increased incidence of bloat, acidosis or other metabolic problems as related to the digestive system.

·Reduced firmness of the manure.

On the positive side, however we see improved gains, improved feed conversions, improved marbling and overall carcass quality, all of which are considered desirable. (Table 2)

1. Megacalories per lb.

2. Non-fibrous carbohydrates or starch

Note: The ingredients and values used in table 2 are very general and are for illustration purposes only. An actual feeding program of this nature would vary from this depending on the type of cattle fed, as well as the ingredients available.

Fermentation Manipulators

Several feed additives are well know for their ability to manipulate fermentation in the rumen. By manipulate we commonly mean select for certain types of microbes, the results of which provide enhanced rumen function for the purpose desired.

The most commonly used products of this nature are the ionophores. The compounds are technically antibiotics and have a negative effect on certain types of microbial organisms. The ionophores currently approved for use in beef cattle include Rumensin (chemical name is monensin sodium), Bovatec (lasalocid sodium) and Cattlyst (laidlomycin propoinate potassium). Each of these compounds are delivered through the feed into the rumen where they actively work to alter fermentation patterns. Although different chemical compound with some similarities they work against certain types of bacteria which tend to consume energy components that are useful to the animal. The overall result is that more energy is available from the same amount of feed resulting in improved feed efficiency (less feed required per lb. of gain) and/or improved overall gains. Other benefits such as reduced incidences of bloat and acidosis as well as reductions in incidence of coccidiosis has also been observed when using these types of products. It is a common practice in the feedlot industry to use at least one of these products. Yet another product that is gaining some acceptance is called GainPro (Bambermycin) although it is only approved for use in cattle on grass at this time. The results a are somewhat similar to the ionophores.

Conclusions

Cattle feeding is an interesting and exciting field as long as some understanding of the physiology and mechanics is available. It is not difficult to change feeds or to move from one type of feed to another as long as the cattleman does his homework and uses some common sense. The results are improved performance and profits and that's the name of the game.

Dr. Steve Blezinger is nutrition and management consultant with an office in Sulphur Springs, TX. He can be reached at P. O. Box 653 Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at sblez@peoplescom.net.

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