Requirements vary Forages should be tested to measure mineral content and determine if supplements are required
A balanced nutrition program is designed around balancing calcium and phosphorus needs along with vitamins and trace minerals.
Sometimes these minerals are chemically antagonistic toward each other and prevent animals from absorbing a particular nutrient.
As well, minerals can be tied up in the fibrous material of the feed.
John McKinnon, beef industry research chair at the University of Saskatchewan, said water with high levels of sulfates may also inhibit the absorption of some trace minerals.
“The availability of these trace minerals in the feed ranges from zero to five percent, depending on the antagonists found in the feed or water,” he said in a Nov. 4 webinar.
It is critical to get the right elements to the cow when it needs it most.
For example, a 600 kilogram cow eating two percent of body weight in the second trimester of pregnancy needs 20 grams of calcium per day.
This increases in the final trimester to 32 grams per day. Cows need 30 to 40 grams per day after calving, depending how much they are milking.
Phosphorus follows the same trend, but the requirements are about half of what is needed compared to calcium. Cows need more phosphorus during lactation.
The typical calcium and phosphorus content of Canadian feed varies, which means forages should be tested. However, probably fewer than half of producers do that.
A legume and grass-legume forage tends to be high in calcium at one to two percent and low in phosphorus at .15 to .25 percent. Additional phosphorus will be needed.
A grass type forage is intermediate in calcium and low in phosphorus. A cereal green feed-barley or corn silage has an intermediate level of calcium but a significantly low amount of phosphorus at .1 to .2 percent.
Cereal grains, especially those used for backgrounding or finishing cattle, are low in calcium and have intermediate levels of phosphorus at .3 to .4 percent.
“In almost all cases, growing rations and finishing rations require some degree of supplementation, whether it is through a loose mineral program or perhaps limestone,” he said.
Magnesium and potassium are essential, but the ratios must be heeded.
Winter tetany can be a problem with forages that have less than .2 percent magnesium or high levels of potassium, especially in fields where manure was applied.
“Potassium is rarely an issue in Canada,” McKinnon said.
“It tends to give us more grief through the high levels rather than a deficiency situation.”
The magnesium requirement for lactating beef cows is .2 percent on a dry matter basis.
Zinc, copper, iodine, cobalt, iron, selenium and manganese are all required, and needs vary.
Requirements are low but necessary and are expressed as milligrams per kg or parts per million.
For example, a 600 kg cow consuming 12 kg of dry matter daily requires daily levels of 120 mg of copper, 360 mg of zinc and 1.2 mg of selenium.
A rough off-colour hair coat, depigmentation or possible cardiac failure may signal a deficiency.
Delayed estrus and/or lower fertility may be observed.
Leg abnormalities and stunted growth in calves can happen.
Copper may not be absorbed if the molybdenum content of feed is less than two mg per kg of dry matter.
Copper availability is also de-creased if there is a high concentration of sulfate in the drinking water.
“If you don’t know your situation in terms of molybdenum content in the soil, sulfate levels in your drinking water for the cows, you really don’t now how much copper you will be needing,” McKinnon said.
“We have to come down to local situations and local environment to really understand the copper requirements of your cow. Copper requirements are not static.”
There is also tremendous variability in the type of inorganic minerals and their availability.
Copper oxide is poorly available with probably less than 15 percent available to the animal. Look for sources such as copper sulfate or copper carbonate.
Zinc deficiency can result in reduced growth, feed intake, feed efficiency. Bulls may have reduced testicular growth and abnormal sperm production. Skin abnormalities or hoof problems may occur.
Selenium deficiencies are more obvious and can lead to white muscle disease in calves, poor growth, lameness, reduced immune response and possible retained placentas in cows.
It is only required in low levels. Animals can get through an injection . Some plants also accumulate selenium. The difference between the requirement and toxicity is narrow.