On several occasions in the past we have discussed minerals, both major and minor in beef cattle. Of late I have gotten a larger than normal number of questions concerning what specifically some specific trace minerals actually do in the animal. We are finding with increased regularity that certain specific TM's are not only important but they may be MORE important than we originally thought.
We typically, in some form or fashion, supplement cobalt, copper, iodine, iron, manganese, selenium and zinc. Other TM's have shown some value but are normally required in such low concentrations we don't bother with them.
General Concepts in TM Nutrition for Cattle
Let's take a close look at some of the more critical factors affecting dietary traced minerals as well as the affects of certain TM's themselves.
As the understanding of TM availability in forages improves, a number of factors become apparent. First, TM concentrations in plant tissues is dependent on the availability of these elements in the soil. An example of this is noted in the distribution of Se in plants throughout the United States. In certain geographical regions, soil Se concentrations are deficient resulting in a low Se status in the forages consumed by grazing animals. Conversely, Se may reach toxic concentrations in those plants found on soils with extremely high Se levels. The levels of other TM's found in grazeable forage is similarly affected although the uptake of some TM's from the soil to the plant is not terribly efficient.
A second consideration which must be made is selective grazing patterns by cattle. This selectivity includes not only particular species of forages but specific plant parts as well. A well accepted concept is that selective grazing by the animal can provide a different pattern of mineral element intake than that indicated by analysis of forage samples taken by hand.
It is a generally accepted theory that certain types of plants are richer in certain mineral elements than others. One study reported that herbs and legumes are higher in a number of minerals than grasses. Copper, Zn, Mo and Co are typically higher in legumes than grasses whereas Se and Mn tend to be higher in grasses.
Another forage factor affecting the availability of TM is plant maturity. A 1978 study evaluated the relative availability of a number of minerals, including Cu, Co, and Zn in five tropical grasses at various stages of maturity. It was concluded that as forages neared maturity, mineral content declined. This decline results in response to a natural dilution process as the plant grows. Plant concentrations of K, Na, Cu and Zn were notably lower as plants increased in maturity. Digestibility of Cu as well as Ca, P and Na also decreased.
These are only a few examples of the limitations to the availability of TM in the diets of cattle grazing range and pasture. One of the most significant problems to determining whether the available forage is meeting the TM needs of the animal is that of actually identifying the specific problem or deficiency as many TM have very similar deficiency symptoms. An understanding of TM function is helpful in identification of potential problems as well as their alleviation.
The Role of Co, Cu, Se and Zn in the grazing animal
In order to properly discuss the action of the TM of interest in grazing cattle, it must be understood that a complex system of interactions exists between the TM as well as other minerals within the body. These interactions are partly responsible for the complexity of determining TM nutritional requirements in cattle. The factors previously discussed affecting mineral availability from grazeable forages compounds this problem, creating a challenge to the nutritionist of enormous proportions. The availability of one mineral in the plant can greatly reduce the capacity for another mineral to be taken up by the digestive tract of the ruminant. An obvious example of this is the relationship that exists between Cu and Mo. High concentrations of Mo in plant tissues can greatly reduce Cu absorption. A similar response for Cu absorption was noted by grazing sheep when Fe levels were increased. Workers noted that ingested Fe may have originated from groundwater and soil intake. Another possible factor increasing plant uptake of Fe is waterlogging of soil in areas prone to high rainfalls. Other studies have indicated that forages grown on acidic soils may exhibit extremely high Fe concentrations thus further depressing the Cu status of the animal.
This is only a couple of the multitude of interactions existing between TM and their utilization by grazing animals.
To speak of the requirement for Co in ruminants is to actually speak of the need for this mineral by the ruminal bacterial population which utilize Co in the synthesis of Vitamin B12. The importance of Co and B12 becomes apparent when the observation is made that the main source of energy to ruminants is not from glucose as in monogastrics, but from the metabolism of acetic and propionic acids (primarily propionic). Vitamin B12 is required for the enzymatic activity which facilitates the production of glucose from propionic acid. Thus the importance of Co for energy metabolism in the ruminant becomes obvious. Deficiency of Co is not readily distinguishable due to the fact that it carries with it the same symptoms as those noted with malnutrition due to reduced intake of protein and energy. Another symptom which helps to distinguish between these two conditions is the appetite depression which accompanies a Co deficiency. Cattle deficient in Co respond quickly to treatment by rapidly regaining appetite as well as improved weight gain.
Plants vary in the degree to which Co may concentrate. One study as early as 1977 reported that legumes tend to have a much greater affinity for Co than do grasses; this factor also largely dependent upon availability of Co in the soil. Cobalt deficiencies may occur under many different soil conditions but are largely found in coarse soils, sandy loams and leached sands. Soil type as well as those soils located in areas of high rainfall, which may encourage leaching of Co from topsoils, aggravate the status of Co in plants. Soils deficient in Co may be treated by utilization of Co-containing fertilizers often with the addition of as little as 100-150 gm of CoSO. However, under extensive range conditions the use of such fertilizers is impractical and uneconomical. A more practical means of treating Co deficiencies in grazing ruminants in both range and pasture situations appears to be through mineral/trace mineral supplementation offered free-choice in areas frequented by the animals such as around stock ponds, etc. Although this method does not provide a totally fool-proof method of providing Co to grazing animals, it is much less labor intensive and less time consuming than the administration of B12 injections or oral dosing or drenching with Co solutions.
Copper is among one of the most important dietary TM and is frequently among the most common TM to be found in a deficient status among grazing livestock. Copper deficiencies are seldom noted in animals allowed access to concentrate diets. A deficiency of Cu in cattle occurs when the dietary level is less than 5 mg/kg DM or when Molybdenum (Mo) or Sulfur (S) are in excess.
Copper is required for hemoglobin production, Fe absorption from the small intestine and Fe mobilization from tissue stores. Copper is also a component of various body pigments (thus the change in hair color patterns during deficient status) and is involved in the central nervous system, bone metabolism and heart function.
As previously discussed, the availability of Cu is directly dependent on Mo concentrations in the plant tissues. A 1978 study reported that dietary Cu to Mo ratios less than 2:1 contribute to a Cu deficiency in cattle. Increased dietary Fe is also thought to depress Cu status in grazing cattle. Few recognized Cu deficiencies are thought to originate from low Cu concentrations in the forages grazed. Most decreased Cu status is thought to originate from a conditioned deficiency in which some other compound inhibits Cu utilization as normally required by the animal. Geographical areas noted for soils with elevated Mo and S are highly susceptible to Cu deficiency as well as those with high Fe contents and acidic soils. Pastures fertilized with sulfate based fertilizers may also potentiate a reduced Cu status in the grazing livestock.
A large number of disorders are attributed to deficiency of Cu in grazing animals. Symptoms including anemia, severe diarrhea, depressed growth, hair color change and weak, fragile bones are only a few of the characteristic signs of a clinical depressed Cu status. One of the more sensitive indicators of depressed Cu is
achromatrichia or loss of hair pigment. Black cattle tend to develop a red tinge to the hair coat whereas the hair of red cattle lightens considerably. Hair loss around the eye is also occasionally noted with Cu deficiency.
Although quite a number of methods for providing supplemental Cu to grazing animals have be researched and are in various stages of use, mineral supplements containing 0.1 to 0.2 percent CuSO4, CuCO, and CuO are among the more practical means of providing for cattle Cu needs. Cattle under range or pasture grazing conditions will normally consume adequate quantities of the supplement to maintain Cu status within the animal. Other means of meeting this need may also be accomplished by the application of Cu containing fertilizers to pastures, although not economically feasible under range conditions. Other methods include administration of Cu injections, drenching with Cu containing compounds or the use of Cu oxide needles in bolus form (Cameron et al., 1988). The methods have all proven effective although require increased handling of animals for treatment. Because of this, these methods may often be somewhat impractical depending on the extent of range situations and the availability of labor.
From the examination of only these two minerals we begin to see the complexity of the systems in which they are involved and their importance. In the next issue we'll look at other TM's in this same manner.
Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, TX. He can be contacted at Route 4 Box 89 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.