Source: Alberta Agriculture and Forestry, http://www.agric.gov.ab.ca/
Minerals are essential for the proper functioning of the animal. A problem arises when the feed does not supply enough to meet the animal’s requirements. This may occur because the feed is low in mineral, 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 that are 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 Alberta. 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 cereal forages 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 bone abnormalities 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. 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) nor greater than 7:1.
Table 1. Average Macro-Mineral Analyses of Selected Alberta Grown Feedstuffs
Most forages are marginal in phosphorus content whereas grain is a good source of this element. Phosphorus deficiency can cause poor reproductive performance which shows up as 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. Excesses of calcium increase the requirement for phosphorus.
Reproductive disturbances may be the most costly effect of phosphorus deficiency. Reduced, conception rate and delay in return to heat after calving translates into reduced weaning percentage and weight (see Table 2).
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 and is more likely to occur in older animals.
Forages grown in Alberta normally contain adequate levels of potassium. Grain, on the other hand, is border-line 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, feedlot type rations.
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 Alberta are the problems caused with copper and selenium use in the animal. In the few areas where excess sulphates in the water is a problem, extra copper and/or selenium supplementation may be needed.
Feeds do not contain enough salt (sodium chloride) to meet the needs of livestock. An adequate supply must be available at all times. A prolonged deficiency can result in loss of appetite, unthriftiness and a drop in milk production.
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).
Table 3. Types of Minerals and their Application
Choose a mineral based on what the ration is low in. Feed test to determine this. Once you have found minerals that meet the needs for major elements, check the trace element content. 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 $1.05/cwt. for calves, mineral feeding would have increased gross income by $10,455 (1.05 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.
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 the 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 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
Adapted from “NRC Nutrient Requirement of Beef Cattle”, 1984.
Adapted from Alberta Agriculture Beef Herd Management Reference Binder and Study Guide – 301