Nutritional Requirements for Pigs part 2
These micronutrients serve many important roles in the body. The estimated requirements for the essential vitamins are given in Dietary Nutrient Requirements of Growing Pigs Allowed Ad Lib Feed (90% dry matter) a,b,c and Reproductive Measures and Dietary Nutrient Requirements of Gestating and Lactating Sowsa,b.
This fat-soluble vitamin is essential for vision, reproduction, growth and maintenance of epithelial tissue, and mucous secretions. Vitamin A is found as carotenoid precursors in green plant material and yellow corn. β-Carotene is the most active form of the various carotenes. Unfortunately, only about one-fourth of the total carotene in yellow corn is in the form of β-carotene. The NRC suggests that for pigs, 1 mg of chemically determined carotene in corn or a corn-soybean mixture is equal to 267 IU of vitamin A.
The use of stabilized vitamin A is common in manufactured feeds and in vitamin supplements or premixes. Concentrates containing natural vitamin A (fish oils most often) may be used to fortify diets. Green forage, dehydrated alfalfa meal, and high-quality legume hays are also good sources of β-carotene. Both natural vitamin A and β-carotene are easily destroyed by air, light, high temperatures, rancid fats, organic acids, and certain mineral elements. For these reasons, natural feedstuffs probably should not be entirely relied on as sources of vitamin A, especially because synthetic vitamin A is very inexpensive. An international unit of vitamin A is equivalent to 0.30 mcg of retinol or 0.344 mcg of retinyl acetate.
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This antirachitic, fat-soluble vitamin is necessary for proper bone growth and ossification. Vitamin D occurs as the precursor sterols, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3), which are converted to active vitamin D by UV radiation. Although pigs can use vitamin D2 (irradiated plant sterol) or vitamin D3 (irradiated animal sterol), they seem to preferentially use D3. Some of the vitamin D requirement can be met by exposing pigs to direct sunlight for a short period each day. Sources of vitamin D include irradiated yeast, sun-cured hays, activated plant or animal sterols, fish oils, and vitamin premixes. For this vitamin, 1 IU is equivalent to 0.025 mg of cholecalciferol. The estimated vitamin D requirement of 200 IU/kg for gestating and lactating sows was increased to 800 IU/kg in the 2012 NRC publication.
This fat-soluble vitamin serves as a natural antioxidant in feedstuffs. There are eight naturally occurring forms of vitamin E, but d-α-tocopherol has the greatest biologic activity. Vitamin E is required by pigs of all ages and is closely interrelated with selenium. The vitamin E requirement is 11–16 IU/kg of diet for growing pigs and 44 IU/kg for sows. Some nutritionists recommend higher dietary levels for sows in the eastern corn belt of the USA, where selenium levels in feeds are likely to be low. Vitamin E supplementation can only partially obviate a selenium deficiency.
Green forage, legume hays and meals, cereal grains, and especially the germ of cereal grains contain appreciable amounts of vitamin E. Activity of vitamin E is reduced in feedstuffs when exposed to heat, high-moisture conditions, rancid fat, organic acids, and high levels of certain trace elements. One IU of vitamin E activity is equivalent to 0.67 mg of d-α-tocopherol or 1 mg of dl-α-tocopherol acetate.
This fat-soluble vitamin is necessary to maintain normal blood clotting. The requirement for vitamin K is low, 0.5 mg/kg of diet. Bacterial synthesis of the vitamin and subsequent absorption, directly or by coprophagy, generally will meet the requirement for pigs. Although rare, hemorrhages have been reported in newborn as well as growing pigs, so supplemental vitamin K is recommended at 2 mg/kg of diet as a preventive measure. Generally, hemorrhaging problems can be traced back to the feeding of diets with moldy grain or other ingredients that contain molds.
This water-soluble vitamin is a constituent of two important enzyme systems involved with carbohydrate, protein, and fat metabolism. Swine diets are normally deficient in this vitamin, and the crystalline form is included in premixes. Natural sources include green forage, milk by-products, brewer’s yeast, legume meals, and some fermentation and distillery by-products.
Niacin (Nicotinic acid):
Niacin is a component of coenzymes involved with metabolism of carbohydrates, fats, and protein. Pigs can convert excess tryptophan to niacin, but the conversion is inefficient. The niacin in most cereal grains is completely unavailable to pigs. Swine diets are normally deficient in this vitamin, and the crystalline form is included in premixes. Natural sources of niacin include fish and animal byproducts, brewer’s yeast, and distiller’s solubles. Based on recent research, the NRC increased the niacin requirement to 30 ppm during all phases of growth.
This vitamin is a component of coenzyme A, an important enzyme in energy metabolism. Swine diets are deficient in this vitamin, and the crystalline salt, d-calcium pantothenate, is included in vitamin premixes. Natural sources of pantothenic acid include green forage, legume meals, milk products, brewer’s yeast, fish solubles, and certain other byproducts.
This vitamin, also called cyanocobalamin, contains cobalt and has numerous important metabolic functions. Feedstuffs of plant origin are devoid of this vitamin, but animal products are good sources. Although some intestinal synthesis of this vitamin occurs, vitamin B12 is generally included in vitamin premixes for swine.
This vitamin has important roles in the body, but it is of little practical significance for swine because grains and other feed ingredients supply ample amounts to meet the requirement in pigs.
A group of compounds called the pyridoxines have vitamin B6 activity and are important in amino acid metabolism. They are present in plentiful quantities in the natural feed ingredients usually fed to pigs. The requirement for vitamin B6 in young pigs (5–25 kg) was increased by 3–4 fold in the 2012 NRC publication compared with the previous edition.
Choline is essential for the normal functioning of all tissues. Pigs can synthesize some choline from methionine in the diet. Sufficient choline is found in the natural dietary ingredients to meet the requirements of growing pigs. However, in some studies, choline supplemented at 440–800 mg/kg of diet increased litter size in gilts and sows. Natural sources of choline include fish solubles, fish meal, soybean meal, liver meal, brewer’s yeast, and meat meal. Choline chloride, which is 75% choline, is the common form of supplemental choline used in feeds. If choline is added as a supplement to sow diets, it should not be combined with other vitamins in a premix, especially if trace minerals are present, because choline chloride is hygroscopic and destroys some of the activity of vitamin A and other less stable vitamins.
This vitamin is present in a highly available form in corn and soybean meal, but the biotin in grain sorghum, oats, barley, and wheat is less available to pigs. There is evidence that when these latter cereal grains are fed to swine, especially breeding animals, biotin may be marginal or deficient. Reproductive performance in sows has been found to improve with biotin additions. Although not as clear, there is evidence that reproductive performance also is improved with addition of biotin to corn-soybean meal diets. In some instances, biotin supplementation decreased footpad lesions in adult pigs. For insurance, biotin supplementation is recommended, especially for sow diets. Raw eggs should not be fed to pigs because egg white contains avidin, a protein that complexes with biotin and renders it unavailable.
This group of compounds has folic acid activity. Sufficient folacin is present in natural feedstuffs to meet the requirement for growth, but some studies have shown a benefit in litter size when folic acid was added to sow diets.
Ascorbic Acid (Vitamin C):
Pigs are thought to synthesize this vitamin at a rapid enough rate to meet their needs under normal conditions. However, a few studies have shown benefits in performance of early-weaned pigs under stressful conditions when this vitamin was added to the diet.
Linoleic acid, arachidonic acid, and probably other long-chain, polyunsaturated fatty acids are required by pigs. However, the longer chain fatty acids can be synthesized in vivo from linoleic acid, so linoleic acid is considered the dietary essential fatty acid. The NRC estimates the linoleic acid requirement at 0.1% for growing and breeding swine. The requirement is generally met by the fat present in natural dietary ingredients. The oil in corn is a rich source of linoleic acid.
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