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Nutrition – for Dec. 6, 2010

It is that time of year where we need to think about feed requirements of our cows. It’s a safe bet that the majority of you are calving either in late winter (i. e. February/ March) or in the spring (April/May). As this time approaches, particularly the last six to eight weeks prior to calving, remember that it is one of the most important periods in the cow’s calendar. Requirements for all essential nutrients increase. Failure to recognize these needs can have disastrous consequences.

First, I want to deal with mineral feeding, an aspect of the feeding program that is far-too-often neglected. There are two general classes of minerals supplemented to cattle. These include the macro-minerals such calcium, phosphorus, sodium, chloride, potassium and magnesium. Requirements are usually expressed as a percentage of the diet or in ounces per day. Salt is a combination of sodium and chloride. Cattle require sodium and to meet the requirement for this mineral, salt intake should be approximately an ounce per day. Failure to supplement salt can result in depressed appetite and poor performance. Cattle will actively seek out salt, thus it can be used as a carrier for other minerals. Trace minerals are required in extremely small amounts and include copper, zinc, iron, manganese, cobalt and selenium. Requirements are expressed as milligrams per kilogram of diet dry matter or simply as parts per million (ppm). Trace mineral deficiencies are common in many areas of the country and can be induced by highsulphate water or high molybdenum in the soil.

It is important to understand that cattle require minerals throughout the year. Failure to supplement will result in deficiency states that can result in poor reproductive performance including delayed heat, poor conception rates, abortions or retained placentas. In calves and yearlings, mineral deficiencies can result in poor appetite and growth, lameness, white muscle disease and a general depressed state.

Mineral deficiencies, particularly trace minerals do not happen overnight, rather they tend to result from long term underfeeding. The best approach to avoid deficiencies is to ensure that your cattle are on a year-round mineral feeding program. Mineral supplements are often classified according to calcium and phosphorus content. A 2:1 mineral typically contains two parts calcium to one part phosphorus (i. e. 18% calcium and 9% phosphorus), a 1:1 mineral contains equal amounts of calcium and phosphorus. High calcium minerals (2:1 mineral or limestone) are commonly fed to cattle consuming high-grain rations, as barley is a poor source of this mineral. Cattle on high-forage diets typically are fed a 1:1 mineral as many of our forages contain equal or slightly higher levels of calcium than phosphorus. In cases where the calcium content of the forage is low or suspect, a 2:1 mineral can be fed. These major mineral sources can be formulated to include trace minerals at specific levels for different regions of the country or custom blended for specific operations.

Alternatively, a trace-mineralized salt can be fed. In such cases, cattle consume trace minerals as they consume their daily salt requirement. Care should be taken to ensure that the mineral you are buying contains the proper levels of the required minerals. This can be accomplished by checking the mineral tag. For example when consumed at 1.5 to two ounces per day, a trace mineral should contain 2,500-4,000 ppm of copper; 8,000-12,000 ppm of zinc; 7,500-10,000 ppm of manganese; 40-60 ppm of cobalt; 100-200 ppm of iodine and 30 ppm of selenium. The higher levels are recommended for cases where trace mineral deficiencies can be induced by high sulphate water and/or high molybdenum soil.

Minerals can be fed by a variety of methods. For cattle fed complete mixed rations or pail-fed grain, the mineral can be mixed in with the feed or top-dressed. Free-choice mineral feeding is common however, consumption can be variable. If cattle fail to consume mineral at adequate levels, intake can be encouraged by mixing salt and mineral together at an appropriate ratio. For obvious reasons the mineral should not be allowed to become wet, mouldy or soiled with manure. Placing the feeder near the water supply will influence consumption.

Trace minerals can also be provided to cattle via trace mineralized salt blocks. Similar to regular salt blocks (i. e. red or blue), these products (i. e. brown) are fortified with the essential trace minerals. Caution should be exercised that you do not provide your cattle with access to several sources of trace minerals. It is easy to forget that trace minerals can be in the mineral mix, the salt, the protein supplement and the salt block.

Again, remember that mineral feeding is a year round program — there are no miracle cures that will make up for failing to supplement your cattle.

[email protected]

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JohnMcKinnon isabeefcattle nutritionistat theUniversityof Saskatchewan

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John McKinnon

John McKinnon is a Professor Emeritus at the University of Saskatchewan and a consulting nutritionist who can be reached at [email protected].

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