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RUMEN MECHANICS AND FUNCTION IN BEEF CATTLE - Part III

Steven Blezinger
Ph.D.

Over the last few weeks we've been discussing what makes a cow “work.” More specifically, we have been examining how the digestive system of the cow, characterized by the presence of the first stomach compartment or rumen plays an important role in the types of material a cow can utilize as a nutrient source. As we continue this series we'll begin examining what we can do to effect the ability of the rumen to function (both positively and negatively). We'll take a look at what we can do from a managerial standpoint to enhance the performance we get from our cow herds as well as growing cattle.

One thing I have neglected to do up to this point is provide a good diagram of rumen anatomy. Figure 1 (see below) represents the basic rumen system as it would appear from the right side of the cow. Note that in the rumen itself about 1/3 of the cavity is typically filled with gas while the lower 2/3 is a semi-liquid made up of water, undigested and semi-digested food material, etc.

Figure 2 (see below) provides a representation of the inner surface of the rumen wall. You'll note the carpet-like appearance. These small “fingers” are referred to as papillae and serve to increase the surface area of the rumen wall. In cattle on a high forage diet these papillae are relatively long while in concentrate fed cattle they are significantly shorter. This is due to the lower pH in the rumen of grain fed beef.

As we change the diet of cattle we manipulate not only the bacterial population as we've discussed previously but also the actual physiology and structure of the rumen itself. In this way we also affect how well cattle absorb various nutrients. In certain instances severe metabolic conditions can be created such as acidosis or bloat which can cause sickness and death. This is why it is especially important to be very careful when making changes to the animal's feeding and nutrition program.

Our Own Worst Enemy?

At the end of the last segment I touched on a very common practice by many cattlemen that probably creates more problems than it solves - that of intermittent supplementation. What I mean by this is that it is very common for a cattle producer to go out one or two times per week to check his herd and in the process carry along enough range cubes or supplement for several days that he feeds all at that one time. In other words he goes out on Monday and puts out enough cubes for two to three or more days. Instead of feeding four lbs. per day he feeds 12 lbs. every three days. This carries some serious implications on performance we need to discuss.

As pointed out last time, in the most basic sense, two of the most common types of microbes in the rumen are those which digest fiber (grass, hay, cottonseed hulls, soy hulls, beet pulp) and those which digest starch (corn, milo). On pasture or other high roughage rations, the bacteria predominantly present in the rumen are those which primarily digest fiber, specifically cellulose. When we introduce grains which contain high levels of starch the starch digesters that are present begin the rapid breakdown process of these materials which liberates various organic acids as a by-product. If this acid production is high enough and it begins to drop the overall rumen pH. When the pH drops low enough we begin seeing a reduction in the populations of fiber digesting bacteria. This has a detrimental effect for a time on the cow's ability to break down and digest fiber. This is the case until the pH comes back up as the numbers of fiber digesters begins to rebuild. One great benefit to the bacterial population in the rumen is that it can regenerate itself in a fairly short period of time. However, when a producer comes in and “slug feeds” a large amount of grain in one setting (i.e. 6 to 8 lbs or more) he is creating problems. Yes, for a short period of time he has increased the amount of energy available to the animal but because of the situation described above, he has reduced the cow's ability to digest fiber -- her primary source of nutrients -- for perhaps a day or so. All in all, the nutrients available, particularly energy can be ultimately reduced instead of enhanced.

Another consideration to this is the fact that in any group of cows you have a given social organization or “pecking order.” The more aggressive cows will eat a larger amount of feed put out and the more timid animals will get less. What this means is that if a situation exists where a producer is feeding 8 lbs of grain or supplement every two-three days, some cows may be getting 10 to 12 lbs. at one setting which accentuates the problem described above even more. I am familiar with cases where bloat and acidosis has been created in these circumstances and cattle have been lost to this problem.

When it is necessary to supplement cows with a grain or higher energy product what we want to do is feed them smaller amounts more regularly, i.e., every day, every other day at the most. This helps keep production of organic acids lower and has a less significant effect on the fiber digesting bacteria. Here are some ways this can be accomplished:

1) One option is utilization of supplements that are lower in actual starch. In the past we have discussed use of whole cottonseed as an energy supplement. Cottonseed is high in protein, fat and fiber and as long as we don't feed so much that the fat level gets too high and suppresses fiber digestion, we don't have much of a problem with alteration of fermentation patterns and depression of fiber digesting bacteria populations.

2) Another option is the feeding of supplements that are higher in more soluble fiber. This would include soy hulls, beet pulp, citrus pulp, etc. These ingredients are higher in fiber but because the fiber in these products is more digestible, they provide good amounts of energy yet are not broken down so rapidly that high levels of organic acid are produced.

3) Yet another possibility is feeding a supplement that is self limiting. This can be accomplished by adding limiting agents such as salt (not terribly consistent and it's hard on the equipment) or an anionic compound such as calcium chloride (more expensive). Other limiters are also available but they tend top be pretty expensive as well. A cow can “normally” eat a maximum of about one lb. of salt per day. Mixing one lb. of salt with four lbs. of grain supplement may hold her consumption of the overall product to a total of five lbs., four of which are the grain portion. Remember, this is an average. A lot of cows can eat a lot more salt than others, just like people. Compounds, such as CaCl actually manipulate blood pH to a degree and reduce the intake of a supplement. This is typically accomplished using a lower amount of limiter as compared to salt and seems to be more effective. Other commercially manufactured feed products use limiters such as fish oil and meal which are effective but as indicated above tend to be pretty expensive.

4) Supplements such as liquid feed fed in lick-wheel feeders are often useful. The nutrition here is a little different in that these supplements don't supply large amounts of energy directly. What they do provide is additional needed protein which stimulates microbial growth and activity and ultimately increases digestibility of the forages the cattle may be on. In other words, it provides a tool for the animal to extract more energy from the nutrient base it is already on. This has been seen to be most effective when cattle are on dormant forages or grass hays where the protein content is not sufficient to meet the bacterial population and ultimately the cow's needs. Liquid supplements do provide a certain amount of energy, the energy coming from sugar and other starches as well as fats, but they are not generally designed to be an energy supplement. An additional benefit is that cows will eat a small amount of supplement multiple times per day thus reducing the potential impact on adverse effects to rumen fermentation.

5) Blocks and tubs have gained a lot of popularity over recent years for much the same reasons. They provide intake limitation while also providing a constant source of nutrients. A particular problem with many blocks is that they may limit intake too much and while they do provide some supplemental nutrient it may not be adequate to have the desired effect. Additionally, they tend to be fairly expensive compared to other types of supplement when viewed on a cost per unit of nutrient (i.e., $/lb protein, $/Mcal of energy). However, from a convenience standpoint the benefit is obvious.

The ultimate point is to feed smaller supplemental “meals” more frequently, if we can accomplish this we've gone a long way toward meeting the nutrient needs of the herd.

Feeding and Ration Changes

One of the biggest challenges we face in the beef industry is taking cattle from a forage based diet to a grain based diet. This is what we encounter when we take growing cattle from the pasture with the cow to a grazing operation and on to the feedlot. Typical feedlot finishing rations may have as the fiber component no more than 10 percent of a high fiber ingredient such as cottonseed hulls, gin trash, ground hay, etc. This is drastically different than what the animal is accustomed to when grazing pasture. Fermentation is much more rapid because of the solubility of the carbohydrates, rumination involving cud-chewing is almost non existent, salvia production is reduced thereby reducing saliva production which is a significant buffer to keep acid levels in check in the rumen. To change an animal directly from a high forage program over to a high grain program creates any number of problems, most notably, as we discussed, bloat, acidosis, going off feed, etc. This change need to be gradual and done with extreme care. In the feedlot this change occurs over a period of three to four weeks. It may be even longer in certain circumstances. The whole point is to alter the bacterial population from predominantly fiber digesters to predominantly starch digesters in such a way that it does not adversely affect the animal. This same circumstance presents itself when we place cattle of feed for show. We need the higher energy intake for the gains that are necessary but at the same time we need to be sure to maintain the health of the animal.

In the next issue, I'll provide some examples of how this feeding program change can be implemented and how it is commonly performed in the industry. Management of cattle requires that we understand how the rumen works and how we have to manipulate this complex system. While there are still many issues we don't understand, a lot of experience has been gained in how to handle these circumstances in an effective, profitable manner.

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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