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Virginia Cooperative Extension -
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Mineral Supplementation for High Grain Diets to Beef Cows

Livestock Update, January 2008

Dr. Mark L. Wahlberg, Extension Animal Scientist, VA Tech

Feeding programs for beef cows this winter may use higher levels of grain or grain byproducts because the amount of hay available is limited.  Hay can be fed at as low as ½% of body weight each day, which converts to 6 or 7 pounds of hay daily, if the hay supply is extremely limited.  It is more likely that hay will be fed at 1% of the body weight of cows, or more.  Even at this level, though, grain or grain byproducts will be needed to provide a fair portion of the nutrition of the diet.  Diets of 10 to 15 pounds of hay each day, plus around 10 pounds of grain or byproduct, will provide adequate protein and energy for beef cows during late pregnancy.

While the primary nutrients will be provided, a critical look must be given to the micronutrients, which means vitamins and minerals.  Forages typically provide a fairly balanced profile of minerals and vitamins relative to the needs of a cow.  However, the grains do not.  In table 1 the mineral and vitamin levels of late-cut Orchardgrass hay and various grains and byproducts are shown.

Table 1. Selected Minerals and Vitamins Contained in Hay and Various Grains
(Values shown are Concentration in the Dry Matter)

Mineral or Vitamin

Orchardgrass Hay

Corn Gluten Feed

Soy Hulls

Brewers Grains

Distillers Grains

Calcium, %






Phosphorous, %






Magnesium, %






Potassium, %






Copper, ppm






Selenium, ppm






Vita A, IU/lb






Values taken from NRC, 2000

A quick comparison determines that the grains have a lot more Phosphorous, Magnesium, and Selenium than does the hay.  Also, the grain products have a lot less Vitamin A and Potassium.  The levels of other minerals (Calcium and Selenium) is variable with the grain product.  Note that Corn Gluten Feed (CGF) is considerably lower in Calcium and Copper than the other feeds. 

Based on these values, the mineral-vitamin supplement must be designed differently when feeding higher levels of grain than when the whole diet is nothing but hay.  Calcium must be included, and Phosphorous is not needed at all.  Vitamin A may be too low, but Copper and Selenium are less likely to be deficient.

When cows are on straight hay or pasture, the recommended complete mineral contains Calcium and Phosphorous, in around a 2:1 ratio.  Also included in that normal cow mineral will be Selenium, Copper, Magnesium, Vitamin A, and many other additional minerals.

When grain or grain byproducts are fed at 10 pounds per head per day or more, the Phosphorous level is more than adequate, so no additional Phosphorous should be provided.  So, the normal cow mineral is not appropriate.  Instead, additional Calcium must be brought into the feeding program, without including any more Phosphorous.  This is the situation with feedlot steers being fed a high grain ration.  Thus, the mineral supplement for feedlot steers would come pretty close to meeting the needs of the cow when she is also fed a high grain ration.  However, this mineral may not be readily available in our area, since few feedlots exist.

One advantage of the feedlot-type mineral is that it may include the feed additive Rumensin.  Rumensin helps cattle obtain more energy from the feed they consume.  When cows consume around 200 mg of Rumensin daily, they improve their feed utilization by around 10%.  In a situation where cows may be thin and feed is in short supply this would be a real help.  This use of Rumensin is approved by FDA.

Many producers are feeding a well-formulated complete mineral for cows, but it is formulated to be a supplement to hay or pasture-based feeding programs.  Adding Calcium to this regular cow mineral will definitely help.  This can be done with Feed-Grade Limestone, which contains 34% Calcium and no Phosphorous.  Most cow minerals are formulated to be consumed at 3 to 4 ounces per head per day.  With this kind of mineral, Limestone can be added at the rate of 12 to 15 pounds per 50-pound bag, mixed thoroughly, and offered free-choice to the cattle in a covered mineral feeder.
***Note that if Corn Gluten Feed is fed at 10 pounds per head or more daily, then limestone must be added to the mineral at a higher rate.  20 pounds per 50-pound bag is the recommended rate in this circumstance.***

Another approach is to add limestone to a high-Selenium Trace Mineral Salt.  These trace mineral salts typically have around 96% salt, trace levels of many minerals, including Copper and Zinc, and Selenium is included at 90 ppm.  But these salt products contain no Calcium, Phosphorous, Magnesium, or Potassium.  However, Calcium is the only mineral needed if the cows are getting more than 10 pounds of grain daily.  Therefore, a blend of 1/3 feed-grade limestone and 2/3 High-Selenium Trace Mineral Salt can be made and offered free-choice to the cattle.  ***Note that if Corn Gluten Feed is fed at 10 pounds per head or more daily, then the limestone-High-Selenium Trace Mineral Salt mixture should be 50-50, and offered free-choice to the cattle.***

A final concern with high grain feeding systems is the Vitamin A situation.  Cows obtain abundant Vitamin A from green forage, and can store quite a bit in their liver.  This can be mobilized to meet the Vitamin A needs when the cow is not consuming an adequate amount.  However, this surplus eventually gets used up.  If a low Vitamin A feeding program is fed for 3 months or more, the cows will need additional Vitamin A in order to prevent a deficiency.  This can be provided in the feed, mineral, or via an injection.  While we would recommend that the feeding supplement be fortified with added Vitamin A, the injection in late winter may be a good alternative.  Consult with your veterinarian about doses and timing of the Vitamin A injection.

When coming out of the winter feeding program next April, there will be a strong tendency to stop grain feeding and start using the new grass which grows.  This is when grass tetany is most likely to occur.  Make sure to switch back to the high Magnesium Cow Mineral (High Magnesium contains at least 10 – 12 % Magnesium in the formulation) about a week before the other parts of the feeding program are changed.  Remember that the grain was providing extra Magnesium, and when grain feeding stops, so does this source of Magnesium.  It must come from the mineral, because the hay/grass do not provide enough.  Do not overlook this important conversion in the mineral program as the cows are converted to a pasture-based feeding program next spring.

Conclusion:  High grain feeding programs, in which Phosphorous is in excess and Calcium is deficient, require different mineral formulations.  Other minerals are less likely to be deficient with high grain rations.  Calcium can be added in 3 ways.

In addition, Vitamin A is likely to be inadequate, resulting in deficiencies occurring in late winter or early spring.  Switch back to the high-Magnesium cow mineral as the feeding program moves from hay-grain to pasture to prevent grass tetany.

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