GRAIN PROCESSING HAS POSITIVE AFFECTS ON PRODUCTION - PART II
by: Stephen B. Blezinger
A couple of issues ago we started a series on the effects of grain processing on the gain and feed efficiency performance of livestock. Here we pick up with the second part of this series, delving more deeply into the cause and affects of the various types of processing described and what some of the nutritional effects are.
Effect on Starch Availability – The Main Energy Source
The digestion and utilization of starch in the ruminant is amazingly complex, primarily because there are so many factors that play a role in the process. As discussed previously the processing of the grain plays a significant role in how the starch within the grain is presented to the rumen bacteria and how it is either broken down at this point or is passed on for further digestion in the lower digestive tract. This processing also directly affects how the starch particles and compositional molecules are also presented to the digestive process.
Remember for a moment why the availability of starch is important in the ruminant animal, be it a dairy cow, a growing calf, a range cow or a feedlot steer. Starch provides for the animal a substrate for two major processes.
1) As starch is broken down by the rumen bacteria, organic acids such as acetic and propionic acid are produced. While these two acids have different functions in the body and higher concentrations of one may be preferential over the other depending on the type of animal (i.e. a dairy cow vs. a feedlot steer) these acids are precursors for important metabolic pathways. Acetic acid enters a pathway by which fatty acids are produced while propionic enters that path which results in the production of glucose in the liver and is subsequently used for energy by the animal. Acetic acid can also be used for this process but it is a more indirect process and less efficient.
2) As the starch particles and submolecules are broken down the result is a supply of carbon skeletons which are available to the bacterial population. The microbes can combine these carbon chains with nitrogen (ammonia) cleaved from intake protein to form protein of their own (microbial protein). This protein makes up the majority of the protein available to the animal as the bacteria are passed down the digestive tract.
As you can see based on this information, starch availability and digestion is required for two very major roles, i.e. energy and protein production.
The starch in corn is found in two main forms -- amylose and amylopectin. Both of these molecules are made up of chains of glucose molecules bound together in beta 1-4 linkages. In other words one glucose molecule is bound at it's No. 1 carbon to the No. 4 carbon of the next and so on. Amylose is basically a straight chain of these glucose molecules while amylopectin has many branches in the chain. The entire starch granule is made up of clusters of these molecules. Amylopectin is more digestible than amylose because of its branched chain configuration. This simply provides more access points for starch digesting enzymes. Normal corn contains approximately 25 percent amylose and 75 percent amylopectin. Research has shown that these numbers can be altered and the amylopectin concentration can be increased through bioengineering. Obviously though this opens up a whole new can of worms. The theory is that this should increase the digestibility of the corn starch as-is. Interestingly, in research done at North Dakota State and the University of Minnesota no significant differences were noted in the milk yield and composition between cows fed high amylopectin corn and those fed conventional varieties.
Starch Gelatinization Dynamics
It would appear at this point that the greatest effect on improving starch digestion in the rumen occurs when it is processed through a method such as steam-flaking. Steam flaking subjects the grain to high temperatures and moisture in the steam cabinet. This allows the heat and moisture to enter the starch matrix of the individual kernel. Mechanical pressure is then applied which, when combined with the previous effect causes the starch to expand and disrupt. The term applied to this process is referred to as gelatinization. When exposed to water starch granule swell although without the applied heat the change may not be noticeable. Heating breaks the intermolecular bonds to allow significant swelling. This swelling of the starch-water mixture then becomes translucent and forms a “gel” as it cools and intermolecular bonds are allowed to reform. Because the amylopectin molecules are branched, they interfere with themselves and cannot reform into a tight, firm structure, therefore leaving the starch matrix more open and susceptible to microbial and enzymatic activity. The degree of gelatinization is typically considered an indicative measure of the improved digestibility of the starch. Gelatinization values of 50 to 68 percent and higher are commonly observed in operations such as feed-yards which feed the flaked grain within hours of it's production.
Gelatinization values are often cross-reference with flake densities which provide an indication of moisture uptake and how well the rollers on the mill are set and the thinness of the resulting flake. Unpublished data by Plascencia and Zinn in 1996 examined the effect of steam-flaking and flake density on production in dairy cows. Steam flaked corn (SFC) with flake densities of 20, 25 and 30 lbs. per bushel were produced. Dry-rolled corn (DRC) was also used in this trial and had a density of 40 lbs. per bushel. These variations were fed in TMRs at 39.5 percent inclusion along with 43.4 percent alfalfa hay as well as the necessary protein, minerals and vitamins. Improvements in performance were noted as follows for SFC fed cows compared to DRC:
Other changes noted were:
• Decreased acetate to propionate ratio.
• Quantity of microbial N produced per unit of organic matter fermented in the rumen was greater.
• Ruminal ADF digestion was reduced.
• Calculated Net Energy value was increased by 33 percent (from .83 to 1.1 Mcal/lb).
The researchers suggested from this and other studies that the optimal flake density should be between 25 to 30 lbs. per bushel.
A conservative estimate would be to use an energy value for SFC that is 10 to 15 percent higher than cracked or coarsely ground corn grain. This is, however, only an estimate and will change as more research data becomes available. Another thought is that when we examine the dry matter intake levels of the two rations we see improved dry matter intake in the flaked corn rations. We know that flaked corn is more palatable primarily because it has a better texture than ground corn. So in this case part of the benefits may be derived from a product that the cattle simply like better.
As gelatinization and flake densities are regressed we find that a point of diminution occurs where decreased flake density may yield higher gelatinization values but because of other physical considerations such as increased fines in the bunk, performance is not improved. This simply means that although we may have slightly lower gelatinazation values than is possible, as indicated above, achieving optimal bushel weights can and do improve performance over attempting to maximize starch gelatinization.
Starch gelatinization and flaked grain bushel weight provide indicators to the producer of the degree of starch availability and digestion possible. Increased use of these indicators and techniques can allow us to better estimate performance and to optimize economic return of rations utilizing various means of grain processing. It is important that we understand what can and cannot be accomplished by different processing methods. In the next issue we will continue this dicussion a bit more by looking at what type of effects can be observed in cattle fed grains processed in different ways.
Choice of Processing Technique
In the first part of this series, we looked at a number of the different processing methods in existence. Choice of processing technique is highly dependent on the cereal grain to be fed. A given processing technique may be very desirable for one grain, but quite detrimental to another. Corn may be fed without any processing, but not milo. Pressure treating appears to be desirable for milo, but harmful to wheat.
Comparison of grain processing techniques is difficult because there are a number of interactions between processing technique and roughage level or type of ration fed. To illustrate this problem, data from Ohio State University has shown that whole shelled corn was superior to crimped corn in very low roughage rations, whereas crimped corn was clearly superior in high roughage rations.
Corn is probably the most commonly fed grain there is. Let's look, for instance, at corn processing. In most instances we find corn fed in one of five ways:
Each of these feeding methods creates some unique circumstances which must be accounted for in feeding and in the situation in which it is fed.
Whole corn -- has been fed as such for years. Recent research in Ohio and other areas of the upper mid-west has shown that whole corn can be fed with good results especially in feeding programs where lower levels of fiber are present. The presence of the intact grain prevents fermentation in the rumen from occurring too rapidly where it might otherwise create a bloating or acidotic response. Concern is often directed to the presence of intact grain within the manure. Some studies have shown that much of the starch has been extracted even from this seemingly intact kernel and that the remaining material observed is predominantly the seed coat.
Feeding of whole corn is the least expensive since it does not incur processing costs which may range for $5 to $20 per ton depending on the facility and the process.
Ground Corn -- Ground corn is produced by running the grain through a hammer mill which pulverizes the grain. Finely ground corn is probably most useful in a pelleted feed. While it does increase the starch availability and digestibility over whole corn, the finely ground material can actually reduce intake because of the level of fines. This observed effect is due to reduced palatability, not a nutritional modification. Fine grinding can also lend itself to an increase in bloating and acidosis due to increased rate of fermentation. Higher levels of fines have also been shown to increase bloating. Used correctly, finely ground corn shows an increase in energy availability of about five to six percent, depending on your data source, over whole corn.
Ground corn typically costs about $5 per ton more than whole corn.
Cracked Corn -- Also referred to as corn chops. Cracked corn is produced by running the grain through a roller mill with the very fine material screened out resulting in a larger corn particle. This opens up the seed coat and allows increased access to the interior starch. This results in an increase in energy availability. Although this process does not process the grain as extensively as fine grinding, since the amount of fines is reduced it does allow for a higher level of intake thus resulting in improved performance in many cases. Thus, like finely ground corn, cracked corn can result in an improvement in performance of about five to six percent.
Cracked corn also will run about $5 per ton higher than whole corn.
Steam-Rolled Corn -- Steam-rolled or steam-crimped corn utilizes a roller mill similar to that used in cracking. However, prior to the rolling process the corn flows slowly down through a steam cabinet which subjects the grain to moisture and heat and “softens” the grain prior to rolling. This prevents the grain from actually breaking up into multiple pieces. It simply mashes the kernel, flattening it to a degree but also creating cracks or breaks in the seed coat, allowing for exposure of the interior starch. Additionally, the heating causes a “gelatinization” of the starch which opens the starch molecule up and allows for even more digestibility. Overall, this creates a larger particle with better digestibility thus stimulating intake while increasing the starch availability. Typically, feeding of steam-rolled corn will result in approximately six to seven percent improved performance over whole corn.
Steam-rolled corn can cost anywhere from $5 to $12 more per ton when compared to whole corn.
Steam-Flaked Corn -- the primary differences between steam flaked and steam rolled corn is that corn going through a steam flaker will reside in the steam cabinet longer, resulting in a higher moisture content at the point of entering the rollers. Secondly the rollers themselves are set closer together resulting in a thinner particle or the creation of an actual flake similar to what you get out of a cereal box. The entire process also creates a greater degree of gelatinization thus increasing starch digestibility even more when compared to steam-rolled corn. Steam flaking is commonly used in the feed yards where maximum starch digestibility and maximum energy availability is vital. Steam flaking will tend to improve performance 8 to 10 percent over whole corn.
Steam-flaked corn will routinely cost $10 to $15 over whole corn.
Similar processes are also available for other grains as well. If you evaluate milo or grain sorghum, for instance, you see that because of the configuration of the grain itself, it simply has to be processed in some manner. Whole milo is very difficult for the rumen bacteria to penetrate and the seed coat must be mechanically ruptured for any type of acceptable digestion to take place. Fine-grinding is not the best answer with milo since is creates a material which can also lend itself to an increase in bloating and acidosis. As-is, it reduces consumption because of the amount of fines in the bunk.
Finely ground milo is better suited for pelleting and used in “reformed” feeds. Cracking or steam rolling of milo tends to be the process of choice since it opens the grain but does not create such a small particle as to promote other digestive problems. Steam-flaking is the process of choice but is not always available.
Similarly, wheat can be processed in the same manner but must be used carefully in order to prevent excessive consumption in too short of a time frame. Wheat starch is highly digestible and ferments rapidly in the rumen. Ground wheat should be fed only as a portion of the grain source (no more than 30 to 50 percent) to prevent and increased incidence of bloating and acidosis.
Nutrient Values of Processed Grains
If we compare nutrient levels side to side, we can see some of the differences that processing makes for different grains. These differences are primarily noted in the energy levels, i.e. Total Digestible Nutrients (TDN), Net Energy Maintenance (Nem) and Net Energy Gain (Neg). You also see some small changes in dry matter content when moisture or steam is used in the process. The following table elaborates on some of these numbers.
As you can see there is a fair amount of variability in the nutrient levels, especially energy in different grains and in different processes. It comes down to comparing what is available and what each source can be purchased for. In many situations it is determined by what types of equipment the feed manufacturing facilities in your area has.
Many opportunities exist in feed formulation and management to improve performance and cost effectiveness of your feeding program. In many situations it is simply a matter of determining what is available and taking into considerations the limitations and benefits surrounding the various grains and processing forms available.
Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.