|Article Index||"Salt and Trace Minerals in Animal Nutrition and Agriculture"||Article Index|
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SALT AND TRACE MINERALS IN ANIMAL NUTRITION AND AGRICULTURE
Animal nutrition is a major market for salt, both for commercial livestock, poultry and fish production and to nourish healthy pets, like cats and dogs. Beyond animal feeding, some soils require salt fertilization for maximum crop yield or nutritional quality. On the other hand, saline soils severely challenge agricultural production in many areas.
For thousands of years it has been known that domestic and wild animals need salt just as man does, and not just for flavor. The virtues of salt for animals were extolled by the ancient Greeks. Early explorers in Africa, Asia and North America recorded observations of grazing animals traveling to salt springs or deposits to satisfy ravenous appetites for salt. Animals deprived of salt will risk grave danger or resort to unusual behavior to obtain it. Considerable evidence exists that early nomads and hunters took advantage of this fact to lure and capture animals by locating areas with salt and waiting for animals to come there periodically.
Salt is unique in that animals have a much greater appetite for the sodium and chloride in salt than for other minerals. Because most plants provide insufficient sodium for animal feeding and may lack adequate chloride content, salt supplementation is a critical part of a nutritionally balanced diet for animals. In addition, because animals have a definite appetite for salt, it can be used as a delivery mechanism to ensure adequate intake of less palatable nutrients and as a feed limiter.
Even though the body only contains about 0.2% sodium, it is essential for life and is highly regulated. About half of the sodium in the body is in the soft tissues of the body; the other half in bones. Sodium makes up about 93% of the basic mineral elements in the blood serum and is the chief cation regulating blood pH. The ability of muscles to contract is dependent on proper sodium concentrations. Sodium plays major roles in nerve impulse transmission and the rhythmic maintenance of heart action. Efficient absorption of amino acids and monosaccharides from the small intestine requires adequate sodium.
The other nutrient in salt, chloride, is also essential for life. Chloride is the primary anion in blood, and represents about two thirds of its acidic ions. The chloride shift, movement of chloride in and out of the red blood cells, is essential in maintaining the acid-base balance of the blood. Chloride is also a necessary part of the hydrochloric acid produced by the stomach which is required to digest most foods.
Unfortunately, it is often assumed that if the sodium requirement is met, the chloride requirement will automatically be met also. However, recent evidence indicates this may not always be the case. For example, Belgian studies showed a close correlation between potassium and chloride in the urine of cows. They concluded that the necessity for the ruminant to eliminate high amounts of dietary potassium (as potassium chloride) can dramatically increase the chloride requirement. Therefore, since many ruminant feedstuffs are quite high in potassium, the potassium-to-chloride ratio in the diet is important.
In monogastrics, a chloride deficiency can also develop when low levels of salt are fed. Leach and Nesheim, reported that a chloride deficiency in chicks results in extremely poor growth rate, high mortality, nervous symptoms, dehydration and reduced blood chloride.
Animals have a more well defined appetite for sodium chloride than any other compound in nature except water. Ruminants have such a strong appetite for sodium that the exact location of salt source is permanently imprinted into their memory which they can then return to when they become deficient. Bell showed that when steers were trained to receive their sodium in response to pressing a panel, maximum effort to receive the sodium occurred at eight days and after, on a sodium deficient diet. Cattle also have a keen sense of smell for sodium. Sodium deficient steers were offered a cafeteria of 12 buckets of water with only one containing moderate levels of sodium salts. Steers would quickly choose the water containing sodium salts without having to taste the water sources.
Horses have been shown to have a specific appetite for salt if the diet is deficient in sodium. This is not true for the other nutrients. For example, horses do not develop a preference for calcium supplements when fed a calcium deficient diet. This natural appetite for salt is what makes salt such an excellent delivery mechanism for other nutrients that need to be consumed regularly, but where a natural appetite is lacking. The 1984 NRC Beef Cattle committee recognized this fact in stating that minerals lacking in the diet can be provided by "self-feeding" common salt-mineral mixtures when the mixture is consumed in amounts to satisfy the animals' appetite for salt.
There are seven trace minerals that have been shown to be needed in supplementing animal diets. They are iron, copper, zinc, manganese, cobalt, iodine and selenium. They are needed in very small amounts, or traces, in the diet, and hence their name "trace minerals."
Subclinical trace mineral deficiencies occur more frequently than recognized by most livestock producers. Currently this is a bigger problem than acute mineral deficiencies, because the farmer does not see specific symptoms that are characteristic of a trace mineral deficiency. Instead, the animal grows or reproduces at a reduced rate, uses feed less efficiently and operates with a depressed immune system. The end result is inefficient production and lower profitability. Therefore, a profitable and efficient farm operation must provide the trace mineral elements. In highly competitive animal enterprises, it can be the difference between profit and loss.
There are several examples where an area of the country was not recognized to be trace mineral deficient in the past but now has been shown to require supplementation. For example, a selenium deficiency was not considered a problem in the United States until relatively recently. Now at least 44 states have been shown to contain low-selenium areas. In only a few states have the classical selenium deficiency symptoms been observed, but performance responses have demonstrated the need for selenium supplementation. When a cobalt deficiency was first found in Western Australia, the problem was believed to be confined to about 5,000 acres. Further studies showed that at least 25 million acres are cobalt-deficient in Western Australia.
Another factor is shipment of feeds from one region to others. This alone makes it almost impossible to isolate areas of specific trace mineral deficiencies. There is nothing to prevent feed grown in a trace mineral deficient area from being shipped to another area where the feed grown is supposedly adequate in that mineral. Grain and soybeans grown in midwestern states with areas deficient in selenium, iodine and other trace minerals are shipped to and fed in many other areas of the United States and the world. Selenium deficiencies have been observed in pigs fed U.S.-produced corn and soybean meal in Taiwan in 1978. Locally grown feeds in Taiwan are usually adequate in selenium.
Salt as a Carrier of Trace Minerals
Salt is a natural carrier for trace minerals, since all farm animals have a natural appetite for salt. Moreover, when cattle, horses, sheep and other animals are on pasture with little, no or varying amounts of concentrate feeding, producers can supply trace mineralized salt free-choice in the form of a mineral block or as loose trace mineral salt in a box. Then, regardless of the amount of concentrates fed, and especially if none is fed, the animal can still consume salt and the trace minerals it contains. The trace mineral levels in salt or salt-based mineral products are guaranteed on the package. Different levels of various minerals are added to salt for specific and different situations. The cost of adding the six trace minerals to salt is very low, ranging from less than one cent for poultry to 81 cents for dairy cattle for a whole year. Horses, beef cattle and dairy goats can be supplied trace minerals with salt for a year for less than 40 cents; and calves, swine, sheep and meat goats for less than 15 cents. This is certainly low-cost insurance compared to the benefits derived. If selenium is also added to salt, at a level of 20 to 30 ppm, the cost will be about 3/4 cent more per pound.
New Trace Elements
As soils decline in fertility and crop or animal yields increase, higher levels of trace elements may be required in animal diets. Molybdenum, nickel, fluorine, vanadium, tin and silicon are some of the trace mineral elements that may become deficient in animal diets in the future. One by one, they may be added to the list of seven trace mineral elements currently being supplemented in animal diets (iodine, copper, iron, cobalt, zinc, manganese and selenium).
When using highly purified or specialized diets, several elements have been shown to be essential. For example, molybdenum is an important part of the enzyme, xanthine oxidase. Fluoride prevents dental caries, may be helpful in osteoporosis, and is needed for growth, and anemia prevention. Nickel is needed for normal reproduction. Silicon is required for growth and proper bone development. Growth rate is decreased with a deficiency of tin or vanadium. Reduced wing and tail feather growth in chicks occurred with vanadium deficiency. Eventually, deficiencies of these trace elements may occur under specialized conditions with practical diets. Already it is known that supplementation of molybdenum, in a few areas where forages contain very low levels of molybdenum, would be helpful in counteracting copper toxicity in sheep.
Nutrition and Disease
An increasing amount of information is accumulating to show that many nutrients are needed at higher levels to improve the ability of animals' immune system to cope with infection. Sodium, chloride, zinc, copper, iron, selenium, phosphorus and magnesium already have been shown to be helpful in this regard. Nutrient requirements for growth, feed efficiency, gestation and lactation do not necessarily mean that those levels will be adequate for normal immunity and high resistance to diseases. Nutrient levels higher than those recommended by NRC may be needed for maximum productivity and health of the animals.
Salt with Additives
Salt can be obtained with or without additives. Most producers add six of the trace minerals (iron, copper, zinc, manganese, cobalt and iodine) and some also add selenium to trace mineralized salt. Salt producers formulate products with additives other than trace minerals. These include other nutrients as well as non-nutritive feed additives. Salt is an ideal carrier of many feed additives because salt is needed by all animals on a daily basis.
Anthelmintics (de-worming agents) may be added to salt. Salt is a convenient means of supplying an anthelmintic for parasite control. Ionophores such as monensin and lasalocid can be added to salt, primarily for cattle and sheep under pasture conditions. Similarly, antibiotics such as oxytetracycline have been mixed with salt and self-fed. This use is most common in a grazing situation. Salt-drug combinations should be fed only if the product is purchased through a feed company or prescribed by a veterinarian.
Vitamins A and D are frequently added to salt. In some cases other vitamins are added, particularly with salt or salt-mineral mixtures for horses, swine or poultry. When vitamins and trace mineralized salts are fed together the mixture should be kept dry to prevent some of the trace minerals from catalyzing the breakdown of the vitamins. Magnesium in salt or salt-mineral mixtures for grass tetany is being used with increasing frequency.
Sulfur is added to certain salt products. Calcium and phosphorus are added when a complete mineral mixture is desired. Specific amounts of calcium and/or phosphorus can be used, depending on the animal or the feeding program. Salt can be used plain, with added trace minerals or with added macro minerals calcium and/or phosphorus.
Forms of Salt to Use
Salt can be provided to animals in many ways. It can be used in the form of loose salt or salt blocks. Loose salt is used in diets mixed for animal feeding. In relatively small pastures, both loose salt and block salt are self-fed to livestock. With very large pastures or extensive range conditions, where mineral boxes are difficult to reach, salt blocks are a good solution. In some cases, they are dropped by airplane onto range areas. Salt blocks can be made for use in specific areas.
About the author: For further information: Online, the Salt Institute publishes useful articles by animal nutrition professionals and college-level course materials for the study of salt and trace mineral nutrition of livestock and poultry and additional FAQs about salt and trace mineral nutrition. Please contact the Salt Institute, National Research Council Animal Nutrition Committee, American Feed Industry Association, Council for Agricultural Science and Technology (CAST), Animal Nutrition Association of Canada, Dr. Larry L. Berger. Dr. Berger's assistance in preparing this page is gratefully appreciated. The FDA Center for Veterinary Medicine is another good source of information. Salt and other ingredients in animal feed are regulated by the Association of American Feed Control Officials (AAFCO). Other sites discuss feeding beef cattle, sheep and horses salt and trace minerals. Walton Feed has information about salt on its website.
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