Source: Manitoba Agriculture, Food and Rural Initiatives
Minerals are essential for proper bodily functions. Problems may arise when the feeds do not supply enough to meet the animal’s requirements. This may occur because the feed is low in minerals, the availability of the mineral is low or another mineral or nutrient is interfering with the ability of the animal to absorb or utilize the mineral.
Macro-elements are those required in relatively large amounts. This group consists of calcium, phosphorus, magnesium, sulphur, potassium and salt (sodium chloride). Table 1 shows the average levels of several of these minerals in some common feed produced in Manitoba. Look at the averages, but most importantly, note the wide variability as indicated by the ranges.
Most forages are good sources of calcium, although some, like annual cereals and corn silage, are marginal to low in this mineral. Grain, on the other hand, is a poor source of calcium.
Calcium deficiency is not very common in animals on mostly forage diets. Deficiency can result in abnormal bone growth and reduced milk production. Cases of milk fever in beef cows are not as prevalent as they are among dairy cattle; however, some cases are reported every year. Prolonged deficiencies of calcium in late prepartum cows can also sometimes be associated with ‘down cows’. This sometimes occurs when cows are fed only greenfeed throughout the winter without an adequate supply of mineral.
Low levels of vitamin D or high levels of phosphorus in the diet may also cause apparent deficiency of calcium. The calcium:phosphorus ratio is important and should not be less than 1:5:1 (i.e., 1.5 parts calcium to 1 part phosphorus) and not greater than 7:1. Cattle can tolerate being fed ratios of less than 1.5:1 however not for periods in excess of 30 days.
Table 1. Average macro-mineral analyses of selected Manitoba-grown feedstuffs
0.63 to 2.86
0.14 to 0.35
|Grass Legume Hay
0.83 to 2.28
0.13 to 0.30
0.36 to 1.43
0.09 to 0.24
0.24 to 0.74
0.10 to 0.26
0.04 to 0.06
0.30 to 0.34
0.55 to 1.02
0.08 to 0.16
Most forages are marginal in phosphorus content whereas grain is a good source of this element. Phosphorus deficiency is linked to poor reproductive performance resulting in irregular heat cycles and reduced fertility.
Other symptoms are reduced feed intake, depraved appetites and, in severe cases, bone fractures. Proper utilization of phosphorus depends on an adequate supply of vitamin D. An excess of calcium increases the requirement for phosphorus.
Reproductive disturbances may be the most costly effect of phosphorus deficiency. As seen in Table 2, reduced conception rate and delay in return to estrus after calving translates into reduced weaning percentages and weight gain.
Table 2. The effect of phosphorus supplementation on reproduction in range cows
|% Calf Crop Weaned
|Average Calving Interval (days)
Source: Alberta Agriculture. 1989. Beef Cow-Calf Manual. (Original source: Wiltbank. 1970.)
Most of the feed we produce appears to be adequate in magnesium. High intakes of calcium and phosphorus reduce the availability of this element. High levels of potassium may interfere with proper utilization of magnesium.
Grass tetany, the most common form of a magnesium deficiency, is not a major problem in beef cattle, although some cases are reported every year. These animals usually have a concurrent deficiency of calcium. Grass tetany is characterized by nervousness, lack of coordination and muscle twitching. The animal may not be able to get up. If not treated promptly, the animal may die. The condition occurs when cattle are grazing lush rapidly growing pasture. In preserved feeds high in potassium such as greenfeed and silage, it is more likely to occur in older animals.
Forages grown in Manitoba normally contain adequate levels of potassium. Grain, on the other hand, is borderline to low in this mineral. A deficiency is not likely to occur in diets high in forages. Potassium supplementation will likely be warranted only on high grain and/or straw based, feedlot type rations. A potassium deficiency is usually associated with reduced feed intake and weight gain and a rough appearance of the animals’ haircoat.
Most home grown feeds contain adequate amounts of sulphur to meet the needs of growing animals as well as dry pregnant beef cows. Lactating cows may be marginal in sulphur, in particular the heavy milkers.
In areas where water is high in sulphates, excess sulphur can be a problem. Excess sulphur can interfere with the absorption and utilization of other nutrients. Of particular interest in Manitoba are the problems caused with copper and selenium use in the animal. In the areas where excess sulphates in the water is a problem, and high molybdenum levels in forage, extra copper and/or selenium supplementation may be needed. See “Evaluating Water Quality for Livestock” fact sheet for further information on sulphates in water. Chelated forms of mineral may be of benefit where high sulphate and molybdenum condition exist.
Feeds do not contain enough salt (sodium chloride) to meet the needs of livestock. An adequate supply must be available at all times. There are some exceptions: Silage produced on land fertilized by manure can increase salt content of forage thus decreasing supplementation requirements. Many of native hays grown in the marshes of lakes Winnipegosis and Manitoba may contain high salt levels. A prolonged deficiency can result in loss of appetite, unthriftiness and a drop in milk production.
Choosing a Mineral
Feed analysis is the easiest method for determining which minerals the feed is low in, and is invaluable in helping to determine which mineral mixes will best meet your needs. Mineral supplements can be classified into three basic categories ( see Table 3).
Choose a mineral based on what the ration is low in, to do this you must have your feeds tested. Once you have found minerals that meet the needs for major elements, check the trace element content. The trace mineral part of this series will help you do this. When you compare mineral supplements, cost per ton is not the only thing to look for. Phosphorus is the nutrient that usually contributes most to the cost of a mineral. As a general rule of thumb, cost per pound of phosphorus can be used to compare minerals that vary in phosphorus content.
Do not be intimidated by the cost of phosphorus minerals. If, for example, we look at the results in Table 2, and assume that this was a 100 cow herd, the benefit of providing phosphorus amounts to 9,957 pounds of extra weaned calf (i.e., 97 calves x 461 lb. minus 79 calves x 440 lb). The cows consumed 36 lb. of mineral per cow per year. The mineral was fed year round. At $1.25/cwt. for calves, mineral feeding would have increased gross income by $ 12,446 (1.25 x 9,957) and the cows would have consumed 3,600 lb. of mineral (1.6 tonnes). At this rate, the cost of the mineral could have been as high as $ 6,534/tonne, and we would still break even. Mineral supplements are nowhere near this expensive.
Table 3. Types of minerals and their application
|Basic Mineral Types
|No calcium – high phosphorus 0:1
|Primarily used with pure legume forage.
|Equal parts calcium and phosphorus 1:1
|Uses primarily with grass-legume, grass, cereal forage and corn silage based diets. Probably the most common mineral type used in Manitoba.
|High calcium low phosphorus 2:1 or 3:1
|Most appropriate for high grain rations. May also be needed in rations using medium quantities of grain with cereal forage or corn silage.
Methods of Feeding
Free choice feeding is by far the most widespread practice. Although it is not as good a method as force feeding or top dressing, it can do the job if managed properly. When free choice feeding, mix salt and mineral together, and feed as the only source of salt. Since most cattle will eat salt and do not always consume minerals, this should force the cattle to eat the mixture to get the salt. Keep track of the amount of salt/mineral mix the cattle are consuming. This is the only way you have of knowing how close you are coming to meeting the animal’s requirements.
The requirements for macro-minerals vary depending on the class of animal, and the level and state of production. Table 4 is adapted from the National Research Council’s Nutrient Requirements Tables. In some cases, a margin of safety is included to ensure minimum requirements are met under a wide range of field conditions.
Table 4. Suggested macro-mineral allowances for beef cattle
|Dry Pregnant Cows
|Average milking ability
|Superior milking ability
Adapted from: NRC Nutrient Requirements of Beef Cattle. 2000.
Agricultural Soils and Animal Nutrition Laboratory
Modified for Manitoba by