Feed additives -- Feed additives are compounds that may elicit a response independent of contributions to the pig’s energy, amino acid, mineral, and(or) vitamin requirements. Typically, these feed additives are added to pig diets in small amounts. In addition, certain nutrients, such as copper and zinc, have been added at pharmacological concentrations (i.e., at high levels the nutrient acts as a drug-see section on nutraceuticals).


Ingredient Quality -- Quality of the ingredients used in swine diets can have a large effect on performance. Test weight of grains, nutrient variability of byproducts and presence of mycotoxins all affect the feeding value of ingredients. However, when properly formulated, diets containing byproducts and weather-stressed grains can provide an economic alternative for swine producers.


Nutrient Interactions -- The absolute requirement for one nutrient can be influenced by the amounts of other nutrients in the diet. There will always be an excess concentration of some nutrients when using common ingredients. In some cases, excesses of one nutrient may cause an undesirable interaction with another nutrient.

Interactions can include mineral with mineral, mineral with vitamin, vitamin with amino acid, and amino acid with amino acid. Although there are many nutrient interactions, only a few are of practical importance when formulating swine diets with common ingredients.


Swine Nutrition Guide: Bioavailability

Bioavailability -- Nutrients present in feedstuffs are not fully available to pigs. Generally, only a portion of each nutrient can be used. This is because feedstuffs are not completely digested and because nutrients occasionally occur in forms that pigs are not able to use.

The portion that is absorbed in a form suitable for use is said to be bioavailable. The amount that is bioavailable depends primarily on the feed ingredient itself. For example, the iron in ferrous sulfate is much more bioavailable than the iron in ferric oxide.

However, there are other factors that also can influence bioavailability. These include the physiological and nutritional status of the animal (e.g., if an animal is deficient in a nutrient, bioavailability is often increased) and interactions among nutrients (e.g., high calcium levels reduce zinc bioavailability). Precise diet formulation recognizes differences in nutrient bioavailability among feedstuffs and is, therefore, based on the bioavailable content rather than the total content of nutrients.

Of course, nutrient recommendations should also be stated in terms of bioavailable requirements, but for many nutrients there is an inadequate amount of data about requirements in bioavailable terms to permit this. In practice, nutrients that have the largest effect on diet cost (e.g., amino acids and phosphorus) usually are formulated on a bioavailable basis. To enable readers to formulate diets on a bioavailable basis and to evaluate more critically ingredients for possible inclusion in swine diets, tables of amino acid, mineral and vitamin bioavailabilities are provided (Tables 3, 4, and 5).

The values for amino acid bioavailability are based on apparent digestibilities at the terminal ileum of growing pigs. Although apparent digestibilities can differ somewhat from true bioavailabilities for some feedstuffs, these digestibilities are widely accepted as similar to bioavailabilities for most common feedstuffs used in the USA. Crystalline amino acids (i.e., L-lysine•HCl, L-tryptophan, L-threonine, and DL-methionine) are assumed to be 100% bioavailable.

Most of the values for minerals and vitamins are based on growth assays using slope-ratio procedures and are relative bioavailabilities (i.e., they are relative to a standard source that is assigned a value of 100%). The bioavailable phosphorus content of feedstuffs is contained in Table 29.


Vitamins -- Vitamins are organic compounds that are required in very small amounts for maintenance, growth, reproduction and lactation.

Some vitamins (thiamin, vitamin B6, and vitamin C) probably do not need to be included in the diet because they are synthesized from other compounds in the body or by microorganisms in the digestive tract, or grain-soybean meal diets contain sufficient amounts to meet the pig’s requirement.

Vitamins are classified as either fat soluble (vitamins A, D, E and K) or water soluble. The water soluble vitamins routinely added to all swine diets include niacin, pantothenic acid, riboflavin and vitamin B12. In addition, biotin, choline and folic acid routinely are added to diets for breeding swine.