ENERGY REQUIREMENTS IN FEED NOT AS CLEARLY DEFINED

by: Stephen B. Blezinger
Ph.D., PAS

Part 4

Over the last few weeks we've been discussing supplementation basics and economics – and how these can be applied by the cattle producer. Up to this point we have largely focused on meeting the protein needs of the animal, the different forms and some of the costs. In our current economy and certainly in some parts of the United States where the drought challenge has been so great, meeting the nutrient needs of cattle herds in a cost effective manner has been challenging. With cattle markets being what they are and what they are projected to be, it makes sense to develop a plan where current ownership and animal productivity can be maintained. The process of rebuilding herds which have been sold down or out completely will be expensive. As such, finding a means of feeding and supplementing these animals affordably is critical.

This entire series has been focused largely on those producers that have a need to purchase any and all supplemental feeds. As referenced above this also extends to those parts of the US that must also purchase forages thus having to incur this additional, elevated cost. So for this group of producers this highlights the need to scrutinize feeding and supplementation costs more closely than ever.

In addition to protein, other nutrients are also important and in some cases critical. In the beef industry, especially in the cow-calf sector, protein tends to be the primary nutrient of concern. It's the nutrient most producers talk about with their feed supplier and is generally the only nutrient they have a reasonably clear idea of when they look at their feeding program. One of the main reasons for this is because protein has been listed prominently on the feed tag. A second reason is that it is also reasonably easy to understand, it's fairly easy to measure and define. What many producers do not understand is that any of the nutrients can, in fact, be the most important nutrient in their program is it is in short supply. The nutrient in the shortest supply can become the limiting nutrient to performance whether it is protein or energy or any of the various minerals or vitamins. Since we've talked about protein to a large degree, let's shift over to energy for a while.

Energy in the Cow

Every living organism needs energy. Energy is like the gas in your car, it's needed to make many if not all of the body processes work properly. All activities of the body require energy, and all needs are met by the consumption of food containing energy in chemical form. The human diet comprises three main sources of energy including carbohydrates, proteins and fats. Of these three, carbohydrates most readily provide the kind of energy needed to activate muscles. Proteins work to build and restore body tissues. The cow's body transforms chemical energy derived from forages and feed by the process of metabolism, an activity that takes place in the individual cell. Molecules of the feed substances providing energy pass through the cell wall. Inside the cell, chemical reactions occur that produce the new forms of energy and yield by-products such as water and waste materials such as heat and those which are later processed into feces and urine. What remains in the body is used for the production of tissue (such as muscle or fat) or milk.

When we limit the amount of energy needed, some of the processes are then limited. The cow's body prioritizes how it uses nutrients and energy is of particular concern. When energy is limited a variety of undesirable affects occur:

1)      Loss of body condition (fat) – while this is often a good idea for people, it is seldom a good thing in cattle.

2)      Reduced milk production.

3)      Reduce growth of calves (both prior to and after birth).

4)      Reduced function of the immune system.

5)      Reduced ability for the animal to keep itself warm or cool.

6)      Reduced reproductive function.

7)      Reduced ability to get out and travel.

So we see that energy is critical. But one of the problems that many producers have is that energy requirement or how to meet that requirement is not as clearly defined. We can see a pound of protein. We cannot see 100 calories of a specific type of energy. Historically, the feed and cattle feeding industry has defined the energy content of a feed or forage in terms of Total Digestible Nutrients (TDN). TDN is a total of digestible fiber, protein, fat and carbohydrate components of a feed, forage or even a total diet. The TDN system is now considered to be unreliable as it tends to under-predict the feeding value of a concentrate (grain, protein source, etc.) relative to forages. Systems more commonly used now include various measurements of the caloric content (for cattle this is measured in units known as megacalories or Mcal). The exact program used may differ depending on nutritionist or company. One of the most common is the Net Energy (NE) system which separates the energy requirements in to their fractional components used for tissue maintenance (NEmaintenance), tissue gain (NEgain) and milk (NElactation) production. These values are calculated from fiber components in the forage or ingredient and take into account the levels of components that release energy when digested (largely carbohydrates and fats). Over time this information has been collected at great length and some predictability is present. Energy levels will vary significantly in some feed components such as forages and by-products. They will vary less in grains and protein meals that are produced by a consistent process. This is another reason why forages should be sampled and analyzed to that the exact energy content can be estimated. Once these numbers are available then “filling in the gaps” becomes feasible.

For the most part, the two primary components in a feed or forage that are considered the energy sources are carbohydrates and fats. Proteins also release energy when they are broken down and digested but this is not a cost effective use for protein sources. Carbohydrates are broken into two broad categories namely fibers and starches. Fiber is itself broken into a number of components such as cellulose, hemicellulose and lignin. These fiber components vary in terms of the ability of the bacteria in the cow's rumen to break these down (cellulose is the easiest, lignin the most difficult) thus the digestibility and a forage's value as an energy source is dependent on the proportion of each of the different fiber components found in a given forage sample. In many cases this is a function of maturity. The older or more mature a forage becomes, the lower the amount of more digestible components such as cellulose will be. At the same time, as the cellulose content declines with age or maturity, the hemicellulose and lignin contents increase.

Fat content of various feeds and ingredients has become of great interest over the last few years because, by weight, fat contains 2.25 times more calories than do carbohydrates and proteins. So less fat can be fed as compared to starch in order to provide the same level of energy. And in a breeding cattle program, feeding of certain fats has been shown to improve reproductive performance even when the cow may not be in optimal body condition. This has led to the theory that these fatty acids provide necessary energy to critical tissues as well as acting as precursors to the production of certain hormones that might otherwise require the presence of a certain level of stored fat in the body. So it has become increasingly common to insure some fat is included in the animal's diet. Fats can only be fed up to a certain level in the diet, however (~6-7 percent). Higher fat levels than this can reduce fiber and other nutrient digestion in the rumen since the fat can coat these particles and reduce microbial access.

Energy Sources

As with protein, let's look at some different energy sources and what they can provide for the animal. To begin, see below a table that lists out a number of different, common feed ingredients that are commonly used to supply energy.


This is just a sampling of ingredients (grains and by-products) that are available for use as energy sources. Many of these can be fed alone to provide for energy needs but consideration needs to be given to balancing the animal's diet and attempting to provide for only one nutrient typically does not work well. Plus each ingredient has special consideration which should be accounted for when feeding. As with protein sources it may be best to feed these as part of a more complete supplement, taking into consideration what is already available from the forage base.

As you can see from the table, each ingredient contains a variety of nutrients so energy is not the only thing supplied. This is also true the high protein ingredients we looked at in Part 1. So combining the right ingredients together, based on the cost of each is essential to providing the best supplement or feed at the best possible cost.

Feeding Methods

In Part 2 and 3 we considered different feeding methods and forms for protein supplements. In many cases a supplement may be formulated to provide primarily one nutrient with only marginal consideration given to the others. For instance, range cubes can deliver significant amounts of energy, in addition to the protein they are designed to provide. They can and in many cases, do, provide supplemental minerals and vitamins. They can provide these IF they are formulated to include significant amounts of these nutrients. What we have run into, especially lately with the high ingredient costs is that many cubes will provide the amount of protein they are designed to but in an effort to reduce cost, other less expensive, lower energy ingredients are used and this reduces the amount of energy that will be delivered in each pound of supplement. This is true with the mineral and vitamin component as well.

It needs to be emphasized that the supplement should be balance with the forage base to meet the animal's requirements if performance is to be maintained. It should be recognized that compromising nutrient content, while reducing cost will also reduce performance and the producer has to ask “how much performance can I give up?”

Conclusion

Again, making good supplementation decisions is not simple and involves weighing a variety of factors. In Part 5 of this series we'll continue the discussion on supplementation and the related economics, tying all the nutrients together so the requirements are provided in a cost-effective, comprehensive package.

Finally, since this is the last article for 2011 I would like to wish you and your family the very Merriest of Christmases and Happiest of New Years. See you in 2012!

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be reached by phone at (903) 352-3475 or by e-mail at sblez@verizon.net. You can also follow us on Facebook at Reveille Livestock Concepts.







Don't forget to BOOKMARK  
Cattle Today Online!