MINERAL INTAKE VARIABILITY A CRITICAL ISSUE

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


Over the years we have discussed minerals and mineral programs at length in these articles. Mineral nutrition, in general, has been studied at great length and for the most part a great deal is known about the importance of minerals in cattle nutritional programs. One particular area concerning mineral feeding and supplementation has comes not in the actual nutrient needs and how we meet those needs from a supplement formulation standpoint but in the actual physical intake of the mineral supplement itself.

The following article will discuss mineral intake in cattle and problems and issues often encountered.

Basic Intake Considerations

Intake of minerals falls into a couple of categories. One is the amount the producer wants the animal to consume and is generally related to cost control. Mineral supplements can be expensive. As such in many cases the producer wants the animal to consume as little as possible in an effort to keep his costs down. This is not a particularly effective viewpoint since in many cases prevents the animal from consuming the amount of mineral needed to truly meet its requirements.

Another key problem that can reduce the effectiveness of a mineral program is variability of intake of free-choice mineral supplements. This intake variation occurs in two ways. One, intake by individual animals within a given herd over a given period of time. It is accepted that within a given group of animals, observations of individual mineral intake will fall into a typical bell-curve plot (Figure 1) common to population data observations in other biological systems.

These intake data, when broken into 1/3s result in fairly general observations over a given herd of animals. Approximately 1/3 of the group will eat less than the targeted intake, 1/3 will eat within an acceptable standard deviation of the targeted intake and 1/3 will consume more than the targeted intake. The results of these individual or group intake patterns when viewed from an overall perspective, might lend the observer to believe that the herd, in general, is consuming appropriate levels of mineral, when, in fact, a full 1/3 may be consuming mineral supplements at a level below that required to maintain an appropriate status of many if not all required minerals. This can be especially detrimental in terms of the trace minerals which are required and fed within a very small window to begin with. For instance, the Beef NRC (2000) indicates the recommended daily requirement of Selenium to be .1mg/kg of overall daily dietary intake. Most diets are formulated at higher concentrations than this. However, given the small required level, even small deviations in supplement intake can result in under consumption of Se.

The animals that may be consuming little or no supplement are obviously at risk for diminished mineral status and may experience a variety of related health and performance issues. Over time this could potentially affect their longevity in the herd. In many cases it will be there animals which are observed to be the “problem” animals in the herd – they don't breed as well, they have more health conditions requiring treatment, etc. The goal here is to minimize the number of cattle which fall into this group although the producer has to accept that there will always be a few.

The second issue here is the group of animals that may be consuming excessive supplement. These animals can likewise experience health and performance issues but due to excessive mineral intake levels or interactions or antagonisms caused by excessive levels. Again, the goal is to minimize the size of this group.

Another measure of intake variability can be noted over periods of time. Figures 2, 3 and 4 below illustrate this fact. These data were collected by a major nutrition company (Vigortone Ag Products a subsidiary of North American Nutrition and Provimi International) who are primary in the manufacture of mineral supplements.

Figure 2 compares the intake mineral supplements provided to cattle while grazing warm or cool season grasses from spring through fall. While intake patterns are similar, mineral intake on cool season grasses are about 31 percent lower than consumption on warm season forages. This means that if the mineral supplement is the same in both instances the intake of all nutrients will also be reduced by this amount.

Figure 3 illustrates intake data collected in a ranch trial in South Dakota over a two year period. Initially intake levels were very high and reflect a cow herd that has previously been on a very poor mineral program or none at all. After about two months, mineral intake decreased to a more normal level (target intake of 4 oz. per head per day). However, over the subsequent 20 months, intake ranged from a low of .75 oz/hd/d to 4.93. Low intakes coincided with the spring of the year when grasses are higher in quality and quantity. Mineral intake is commonly affected by forage conditions. Normally, in most areas, as forages flourish, mineral intake will decline.

Finally, Figure 4 illustrates data from yet another intake trial run in Iowa. In this trial intake over 6½ month trial period ranged from 2.0 to 14.0 oz/hd/day. Again, target intake was 4 oz/hd/d resulting in intakes of mineral supplements ranging from 50 percent to 350 percent of target.

Similar variability has been noted in different studies across the United States (although intake patterns may differ). The net result of this variability is a potentially dramatic variation in the status of critical minerals, often resulting in impaired reproductive, gain or health performance.

Conclusions

We know definitively that intake of mineral supplement can vary significantly for a host of reasons. These include individual animal preference or behavior, forage quantity and quality, time of the year, feeder management, quality, formulation, palatability, etc. of the supplement itself. Obviously some of these factors are out of the producer's control. However, when circumstances such as environment and forage conditions change, it is important to understand how we must mediate these situations by changing management, product type or characteristic.

It is also important that we carefully monitor mineral intake and scrutinize the supplement we are using. Seldom will the same product work continuously in all conditions. Since the herd's health and performance is so closely tied to mineral status it is critical that this aspect of your nutritional management program be attended to carefully.

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, by mail at 667 CR 4711 Sulphur Springs, TX 75482 or by email at sblez@verizon.net.







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