Anti-nutritional factors in animal feed. A brief review

Tannins correspond to a large group of polyphenolic compounds. They are characterized by their solubility and their ability to form complexes. Tannins can injure the intestinal mucosa, interfere with the activity of digestive enzymes with the consequent decrease in digestibility and availability of amino acids and minerals. According to their chemical structure they are classified into two groups:

• Condensed tannins: Commonly found in sorghum grains.
• Hydrolyzable tannins: They have lower anti-nutritional effects than condensed tannins, however when they are found in high doses they can cause ulcers and even the death of production animals.

Chlorogenic acid, a non-tannin phenolic compound, is found primarily in sunflower seeds and is known to generate gray spots on  the egg shell. Lignin is another example of a phenolic compound that does not correspond to the tannin family.

Phytates and phytic acid

Phosphate groups form complexes with various cations and thus reduce the availability of amino acids and other fractions of food. Phytic acid on one hand has the advantage of being a source of phosphorus (when it is accompanied by phytase enzymes that manage to release this mineral), but on the other hand, presents the disadvantage of being an antiutritional factor.

Ergotamin

It is a ANF, produced by the fungus Claviceps Purpurea (known as Ergot), which affects cereal grains. In pigs it can cause food rejection, agalaxy and abortions.

Trypsin inhibitors

Trypsin inhibitors can be found in various legume seeds, the most common being soybeans and beans. Due to the composition of these elements, they can be inactivated with heat, being the wet treatment more effective than the dry one.

In soy the most abundant trypsin inhibitor (about 70%) is called Kunitz inhibitor which is very sensitive to heat. This is not the case for the Bowman-Birk inhibitor, which is more common in processed soybeans due to its greater resistance to high temperatures.

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Anti-nutritional factors of Rapeseed

Glucosylonates are glycosidic substances found in rapeseed (Brassica napus) and other cruciferous seeds. These are fairly stable compounds that remain largely after the oil has been extracted from the seed.

In addition to transmitting a bitter taste, glucosilanates generate metabolites that cause loss of appetite and affections related to the liver and thyroid gland. This effect is due to hydrolyzation produced by the enzyme myrosinase also present in the seed. This enzyme can be inactivated with heat, although it is important to keep in mind that it can also be produced by microorganisms that inhabit the gastrointestinal tract. Which can also generate the same disturbances described above.

For adult monogastric animals the acceptable dose of glucosilonates is up to 1.5 mmol/kg of feed.

Rapeseed also has other types of anti-nutritional factors that decrease the quality of protein and energy in poultry and pigs. These are:

• Erucic acid
• Tannins
• Sinapine (gives fishy flavor)
• Others: sulfur, oligosaccharides, phytates

Levels of rapeseed inclusion in animal feed

Adapted from GG Mateos, 2019

Non-digestible carbohydrates

In general, it is considered that the presence of oligosaccharides impairs animal growth due to the fact that these are undigestible for animal enzymes. As a result they are fermented by microorganisms in the large intestine, causing gas production and diarrhea. However, these effects vary according to the age of the animal and the amount of oligosaccharides present in the diet.

Arabinoxylans y B-glucans

They are carbohydrates commonly found in cereals such as oats, barley, wheat, rye and to a lesser extent, corn.  They generate an increase in the viscosity of intestinal contents in birds, reulting in a reduction of consumption and digestibility.

Hemagglutinins, Saponins, Glycine y β-Conglycinin

These compounds are ANFs present in legume seeds. Hemagglutinins are glycoproteins that bind to carbohydrates in the intestinal mucous membranes generating digestive disorders. These compounds are eliminated when subjecting legumes to oil extraction, which is why they are only relevant in those cases when they are administered as raw seeds.

Saponins are soluble glycosides that are relatively heat stable and are found in legumes such as alfalfa and in smaller quantities in soybeans and beans. Although they are very toxic compounds when administered parenterally, when ingested with food they do not present major problems.

Glycine y β-conglycinin, are globulins found in soybeans. They are proteins that generate hypersensitivity, affecting the immune response and damaging the cells of the epithelial mucosa. Lactating  calfs are more sensitive to these, than pigs or birds. Nontheless their inclusion must be looked after carefully, mainly in recently weaned piglets. Its allergenic activity can be reduced through heat exposure or by extracting the oil.

Cyclopropenoid and Gossypol acids 

Cyclopropenoid acids and Gossypol are anti-nutritional factors present in cotton seed and flour.  The first of these increase in the flour with respect to the seed and cause damage to the vitelline membrane of the egg. They also inhibit the action of the enzyme desaturase, which results in an increase of saturated fatty acids in the yolk. Causing it to become firm, and giving the albumin a pink color.

Gossypol is a polyphenolic pigment that produces various signs such as: loss of appetite, decreased fertility, liver failure and pigmentation of the shell and yolk. During oil extraction, gossypol content is significantly reduced.

Conclusions

The negative effects of anti-nutritional factors on the metabolism and productivity of animals varies according to the species, age, amount of ANFs present, processing, interaction with other nutrients, etc. Knowledge about antinutritional factors is essential when formulating diets for production animals, especially in young monogastrics.