Micronutrient Supplementation
Introduction
1. Trace element requirements in animals are poorly defined and seldom in cow diets are the requirements altered to fit the level of productivity of the cow.
2. There is considerable variability in the level of trace elements found in forages, and the factors that influence this variability are poorly documented.
3. There is tremendous variability in the trace element
content of mineral mixes sold commercially. In fact, it is often difficult
to obtain this information, at least through local sales personnel
(Corah and Arthington
1995).
Conditioning
This term is used to refer to the ability of one mineral element to reduce the availability of another.
For example, an increased availability of calcium will decrease an animal's ability to absorb zinc. High levels of molybdenum will decrease the availability of copper.
True deficiencies of minerals do occur in some areas and these must be addressed by supplementation. However, if cattle are taking in adequate amounts of minerals in their diet, they may not require supplementary minerals at all. High production and stress increase the animal's requirement for micronutrients and selective supplementation may be appropriate.
Water
(Also see Cow Comfort water supply)
It is absolutely essential that the water supply be tested every five years for consumption by livestock.
Water containing high levels of sulfate or iron are antagonistic to the availability of some microminerals.
Nitrate levels of 100m-200 mg/L are potentially dangerous (the total diet should not contain more than 0.5% nitrate).
High water pH >nine (alkaline) predisposes a dairy cow to milk fever. The contribution of sodium, calcium and magnesium by water supplies should be taken into consideration.
Protected Minerals
There are three types of protected minerals: chelates, proteinates and complexes.
An unprotected or inorganic mineral carries an electrical charge which attaches to other molecules, making them too large to be easily absorbed by the gut.
Nevertheless, there are confusing contrary opinions regarding the suggested improved "bioavailability" of protected minerals.
Testing the availability of minerals is usually carried out under strictly controlled conditions using animals that are not diseased or stressed.
I believe that bioavailability may be less important than the effect of flooding the rumen with inorganic supplements, which may combine with and block the absorption of other trace elements.
If a deficincy of trace elements can be identified in the diets of a herd with a high incidence of lameness, those minerals should be supplemented in their protected form.
Iron
Iron can be present in high levels in pasture and forages.
If the level of iron in pasture and forage approaches 300 ppm, other sources of iron should be monitored, particularly the iron present in water.
Deficiencies of cobalt, magnesium and selenium can be induced by high iron intake.
Overloading with iron increases susceptibility to infection.
Maximum safe levels of iron in water are 175 to 300 mg/L.
Mineral supplements containing phosphates may have high levels of iron as impurities.
As little as 300 ppm of iron in the diet can markedly reduce copper absorption.
The negative effects of iron may be counteracted if adequate levels of Vitamin E are available to the animals.
Copper
Copper is essential for the growth of healthy claw horn.
A primary deficiency of copper exists when cattle receive less than 5 ppm of copper in their diet.
Adequate diets contain 10-25 ppm of copper.
Copper levels can vary from pasture to pasture on the same farm, from month to month, and from year to year. In some cases the levels often drop to "marginal" levels, i.e., below 10 ppm.
The availability of copper to cattle is reduced by high levels of protein in the grass or by the presence of high levels of molybdenum which can be accumulated by legumes.
Sulfates in water (>500 mg/L) decrease the availability of copper. Infectious disease and stress reduce absorption of copper.
Copper is less available in silage and young grass than in hay.
Intake of high levels of iron may have a negative effect on copper utilization.
If a lameness problem exists in a herd and marginal availability of copper is suspected, it is highly recommended that a protected form of copper should be used.
Zinc
Zinc is essential for the growth of healthy claw horn.
Stress and disease reduce the amount of zinc in the tissues and presumably increase the demand for the element.
High levels of copper and iron are antagonistic to zinc.
HIGH LEVELS OF CALCIUM IN THE DIET INCREASE THE DEMAND FOR ZINC
It is not unusual for pastures (or forage) to contain marginal levels (10-30 ppm) of zinc. This can vary from season to season, pasture to pasture on the same farm and at different times during the same season.
Alfalfa tends to be rich in calcium as do rations formulated for dairy cows.
For every 0.1% of calcium in the diet over 0.3%, an additional 16 ppm of zinc should be made available.
Sodium
The amount of sodium usually found in pasture or forage is inadequate for the needs of cattle. However, sodium is required for the production of the copious quantities of saliva produced by cows when they ruminate.
The sodium bicarbonate in saliva neutralizes the acids produced during the fermentaion of carbohydrates in the rumen.
Sodium levels in cattle affect potassium levels and vice versa.
Between 0.18 and 0.67 % salt in the dry matter of the total ration of dairy cows is considered to be adequate.
Cattle crave salt (sodium chloride) and can be induced to consume a free choice mineral supplement if 6% salt is added.
Abnormally high consumption of a free choice mineral supplement can be reduced if the salt content of the mixture is reduced and salt is offered separately.
Selenium
It is well known that selenium/vitamin E deficiency causes white-muscle disease. The possibility of deficiency is increased in the presence of linoleic acid which is found in FRESH pasture.
Supplementation of the total dry ration to 0.33 ppm of selenium is recommended (or 25-125 ppm in a free choice mineral mix).
Care must be taken not to over-supplement with selenium. Selenium toxicity can produce clinical signs in the feet such as cracks.
Biotin
We have found that cattle fed biotin are 2.5 times less likely to have sandcracks than those not given the supplement.
In herds with a lameness problem, it is recommended that heifers should be fed 10 mg of biotin per day during their first pregnancy.
Vitamin E
Vitamin E deteriorates rapidly in forage.
Farmers are often reluctant to supplement with this vitamin due to its high cost.
Vitamin E is essential for proper selenium metabolism.
It also has a protective influence in counteracting negative effects of high iron in the diet.
Recommendations
- Do not ignore the possibility that mineral imbalances can be implicated in a herd lameness problem.
- Have forage (and/or pasture) samples tested for trace mineral levels to establish the levels being fed.
- Always take liver samples from dead or slaughtered animals and have them tested for mineral content.
- NEVER "shot gun" by adding additional trace elements to the mineral mix without proper justification.
- If a mineral deficiency is suspected of being implicated in a herd with a lameness problem, use only protected minerals and consider the benefits of using biotin supplementation, particularly with young animals.
