Nutritional Requirements of Pigs

Although used primarily in skeletal growth, calcium and phosphorus play important metabolic roles in the body and are essential for all stages of growth, gestation, and lactation. The NRC estimates requirements of 0.66% calcium and 0.56% total phosphorus for growing pigs of 25–50 kg body wt. The requirements are higher for younger pigs and lower for finishing pigs, but the ratios of calcium:phosphorus are approximately the same for all weight groups. These levels are adequate for maximal growth (rate and efficiency of gain), but they do not allow for maximal bone mineralization. Generally, maximal bone ash and strength can be achieved by including 0.1%–0.15% additional calcium and phosphorus in the diet.

For gestating and lactating sows, calcium and phosphorus requirements are influenced by stage of gestation (the first 90 days versus the final 25 days of gestation), parity, milk production, and other factors ( see Table: Reproductive Measures and Dietary Nutrient Requirements of Gestating and Lactating Sows^a,b). The higher requirements during late gestation are attributed to rapid development of the fetuses. Swine producers may choose to feed slightly higher levels to sows to ensure adequacy of these minerals and to prevent posterior paralysis in heavy milking sows. The calcium and phosphorus requirements listed are based on daily feed intakes of 4.7–5.7 lb (2.1–2.6 kg) during gestation and 13.1–14.6 lb (5.9–6.6 kg) during lactation (these amounts include 5% wastage). If less feed is consumed per day, the percentages of calcium and phosphorus may need to be adjusted upward.

The ratio of total calcium:total phosphorus should be kept between 1.25:1 and 1:1 for maximal utilization of both minerals. A wide calcium:phosphorus ratio reduces phosphorus absorption, especially if the diet is marginal in phosphorus. The ratio is less critical if the diet contains excess phosphorus. When based on digestible phosphorus, the ideal ratio of calcium to digestible phosphorus is between 2:1 and 2.5:1.

Most of the phosphorus in cereal grains and oilseed meals is in the form of phytic acid (organically bound phosphorus) and is poorly available to pigs, whereas the phosphorus in protein sources of animal origin, such as meat meal, meat and bone meal, and fish meal, is in inorganic form and is highly available to pigs. Even in cereal grains, availability of phosphorus varies. For example, the phosphorus in corn is only 10%–20% available, whereas the phosphorus in wheat is 50% available. Therefore, swine diets should be formulated on an “available phosphorus” basis to ensure that the phosphorus requirement is met. The NRC publication expresses the digestible phosphorus requirements as apparent total tract digestible (ATTD) and standardized total tract digestible (STTD) phosphorus. ATTD phosphorus represents the phosphorus digested, and STTD phosphorus is the digestible phosphorus corrected for endogenous phosphorus excretions.

Phosphorus supplements such as monocalcium or dicalcium phosphate, defluorinated phosphate, and steamed bone meal are excellent sources of highly available phosphorus. These supplements also are good sources of calcium. Ground limestone also is an excellent source of calcium.

Phosphorus is considered a potential environmental pollutant, so many swine producers feed diets with less excess phosphorus than in the past to reduce phosphorus excretion. Supplemental phytase, an enzyme that degrades some of the phytic acid in feedstuffs, is commonly added to diets to further reduce phosphorus excretion. The general recommendation is that dietary calcium and phosphorus can both be reduced by 0.05%–0.1% when ≥500 units of phytase per kg of diet are included.

These minerals are provided by common salt, which contains 40% sodium and 60% chloride. The recommended level of salt is 0.25% in growing and finishing diets, 0.5–0.75% in starter diets, and 0.5% in sow diets. These levels should provide ample sodium and chloride to meet the animal’s requirements. Animal, fish, and milk byproducts can contribute some of the sodium and chloride requirement.

Practical diets contain ample amounts of these minerals from the grain and protein sources, and supplemental sources are not needed. Magnesium oxide supplementation has been used to prevent cannibalism, but controlled studies do not support this practice.

These minerals are involved in many enzyme systems. Both are necessary for formation of Hgb and, therefore, for prevention of nutritional anemia. Because the amount of iron in milk is very low, suckling pigs should receive supplemental iron, preferably by IM injection of 100–200 mg in the form of iron dextran, iron dextrin, or gleptoferron during the first 3 days of life (also see Iron Toxicosis in Newborn Pigs). Giving oral or injectable iron and copper to sows will not increase piglet stores at birth nor will it increase the iron in colostrum and milk sufficiently to prevent anemia in neonatal pigs. High levels of iron in lactation feed results in iron-rich sow feces that pigs can obtain from the pen. Iron can also be supplied by mixing ferric ammonium citrate with water in a piglet waterer or by frequently placing a mixture of iron sulfate and a carrier, such as ground corn, on the floor of the farrowing stall.

The copper requirement for growing pigs is low (3–6 ppm) but higher for sows. The estimated copper requirement of 5 ppm for sows in the previous NRC publication was increased to 10 ppm for gestation and 20 ppm for lactation in the 2012 edition.

Copper at pharmaceutical levels in the diet (100–250 mg/kg) is an effective growth stimulant for weanling and growing pigs. The action of copper at high levels appears to be independent of, and additive to, the growth-stimulating effect of antibiotics. Copper sulfate at high levels in the diet results in very dark-colored feces. Also, high copper diets result in marked increases in the copper content of excreted manure.

The thyroid gland uses iodine to produce thyroxine, which affects cell activity and metabolic rate. The iodine requirement of all classes of pigs is 0.14 mg/kg of diet. Stabilized iodized salt contains 0.007% iodine; when it is fed at sufficient levels to meet the salt requirement, it will also meet the iodine needs of pigs.

Although essential for normal reproduction and growth, the quantitative requirement for manganese is not well defined. Manganese at 2–4 mg/kg in the diet is adequate for growth, but a higher level (25 mg/kg) is needed by sows during gestation and lactation.

Zinc is an important trace mineral with many biologic functions. Grain-soybean meal diets must contain supplemental zinc to prevent parakeratosis ( see Parakeratosis). Higher levels of zinc may be needed when dietary calcium is excessive, especially in diets typically high in phytic acid such as corn-soybean meal diets. Pharmacologic levels of zinc (1,500–3,000 mg/kg) as zinc oxide have consistently been found to increase pig performance during the postweaning period. In some instances, high levels of zinc oxide have been reported to reduce the incidence and severity of postweaning diarrhea. Responses to zinc oxide and antibiotics seem to be additive in nature, much like the responses to high copper and antibiotics; however, there is no advantage to including high copper and high zinc in the same diet. Similar to copper, high levels of dietary zinc cause increased zinc content in the excreted manure. For sows, the estimated zinc requirement was increased from 50 ppm in the previous NRC publication to 100 ppm in the 2012 edition.

The selenium content of soils and, ultimately, crops is quite variable. In the USA, areas west of the Mississippi River generally contain higher amounts of selenium, whereas areas east of the river tend to yield crops deficient in selenium. Under most practical conditions, 0.2–0.3 mg of added selenium/kg of diet should meet the requirements. This trace mineral is regulated by the FDA, and the maximal amount of selenium that can be added to swine diets is 0.3 mg/kg.

This trace mineral, which is a cofactor with insulin, is required by pigs, but the quantitative requirement has not been established. In some studies, chromium at a supplemental level of 200 mcg/kg (ppb) improved carcass leanness in finishing pigs and improved reproductive performance in gestating sows, but these effects have been somewhat inconsistent.

Cobalt is present in the vitamin B₁₂ molecule and has no benefit when added to swine diets in the elemental form.

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.

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 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.

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.