Dr. Bill Weiss, Professor and Extension Dairy Specialist, Department of Animal Sciences, The Ohio State University
The cost of mineral and vitamin supplementation is low compared to the cost of providing adequate energy and protein to dairy cows. However, that does not mean those costs should not be scrutinized closely in periods of low milk prices. Calcium and salt are so inexpensive they should be fed in slight excess (e.g., about 20%), totally independent of milk prices. Magnesium and supplemental phosphorus are expensive, but deficiencies can be quite costly. In most situations, you should not buy any additional supplemental P once lactating cow diets contain 0.35 to 0.38% P (diet dry matter basis). However, diets with byproducts, such as distiller grains, wheat midds, and corn gluten feed, often have P concentrations greater than those levels but that P is inexpensive. Magnesium is almost always deficient in basal diets and will need to be supplemented. Cows have very little Mg reserves so if diets are deficient, deficiency signs can develop quickly. Furthermore, basal diets often contain excess potassium which inhibits Mg absorption, increasing the risk of deficiency. In most situations, diets with 0.20 to 0.25% Mg is adequate for lactating cows. The quality of magnesium oxide (most common form of supplemental Mg) varies widely. Be leery of very cheap magnesium oxide because the Mg may not be available to the animal. Feeding products that increase the DCAD (concentration of potassium + sodium – concentrations of chloride + sulfur, expressed as milliequivalents per kg of diet) often increase milk fat yield. Based on a study from University of Maryland, for every 100 unit increase in DCAD (mEq/kg), milk fat yield is expected to increase about 0.75 lb/day. Compare the cost of the buffers to the value of milk fat when determining whether to include buffers in the diet.
Trace mineral supplementation should be evaluated closely during periods of low milk prices. Often these minerals (copper, manganese, iron, selenium and zinc) are over supplemented and simply reducing supplementation rates so that total (basal plus supplemental) minerals are approximately equal to NRC recommendations will cut supplementation costs. In most cases, diets should have 10 to 13 mg/kg (ppm) Cu, 35 to 40 ppm Mn, and 40 to 50 ppm Zn. Supplemental Se should be fed at 0.3 ppm (this does not include basal). Supplemental iron is almost never needed and should be removed from the diet. Cows store trace minerals in the liver so even if these rates are not quite adequate, short term deficiency is very unlikely because of mobilization from the liver. For most cows, in the short term (weeks to a few months) copper supplementation could be reduced below NRC because of liver stores. However because of the effects zinc may have on bacteria within the digestive tract, it should not be reduced much below the concentrations stated above. In the short term, Mn could be reduced to around 25 ppm for lactating cows, but dry cows should be fed at least 40 ppm to maintain normal fetal development. Essentially every study conducted evaluating the economic benefits of selenium supplementation show a very positive return on investment and all diets should continue to be supplemented with 0.3 ppm Se. Another cost consideration is form of trace minerals. The sulfate forms are commonly fed and are usually the least expensive source of minerals. Several commercial forms of organic trace minerals are available, but they almost always cost more than sulfates. Positive responses to high quality organic Zn are likely and some of these responses have longer term implications, such as on hoof health. If you are currently feeding organic Zn, you may want to consider using 50% organic Zn and 50% sulfate Zn to reduce costs but continuing to include some organic Zn is a good idea. Several studies have shown that a blend of organic and inorganic trace minerals works well. Organic Cu should be used when antagonists, such as high sulfur water or high sulfur diets are fed, but if antagonists are not a problem, copper sulfate is probably adequate. The value of organic Mn is not clear and manganese sulfate is likely acceptable. In most situations, selenite or selenite are acceptable forms of supplemental Se, but because of transfer to the fetus, dry cows should be fed a blend of selenite and high-quality selenium yeast.
Because of supply issues, the prices of several vitamins are much higher than typical. Often vitamins are over supplemented; however, most data show that feeding vitamins A, D, and E at about NRC levels (approximately 70,000, 25,000 and 500 IU/day for lactating cows) is adequate. The first recommendation to reducing vitamin costs is simply reduce supplementation to those rates. If additional savings are needed, vitamin A could be reduced below NRC because liver stores are probably adequate in most cows to last several months. Cows do not store large amounts of vitamin D and E in forms readily available to the cow so supplementation should not be reduced much below the above recommendations. An exception is grazing cows because fresh pasture is an excellent source of vitamin E, and sun exposure allows the cow to make vitamin D. For grazing cows, supplementation rates for vitamin D and E could be cut in half without any issue.
Supplemental biotin increases milk production and improves hoof health. Unfortunately, the price of biotin is quite high now because of manufacturing issues. Hoof health has long term implications; therefore, if you are feeding biotin to improve hoof health, I would not remove it from the diet. Studies with beef cattle suggest that 10 mg/day (rather than the standard 20 mg/day) may be enough; therefore, consider leaving biotin in the diet but at half the normal supplementation rate.