Common Anti-nutritional Factors in Animal Feed Ingredients

Have you ever wondered why your animal, when fed with some particular animal feed, experiences a slow growth rate or stunted growth?

This is as a result of the antinutritional factors present in the feed ingredients. Anti-nutritional factors (ANFs) are substances present in feed ingredients that can reduce nutrient utilization and impair animal performance. They are also called the antinutrients.

Some common examples of antinutrients found in animal feeds include phytate, glucosinolates, saponins, tannins, lectins, protease inhibitors, and non-starch polysaccharides. This article will help you understand antinutritional factors and how to remove them.

feed ingredients

Effects of Antinutritional factors

These ANFs can act in different ways to negatively impact animals, such as:

  • binding to nutrients and reducing their absorption,
  • interfering with digestion,
  • impairing protein and carbohydrate metabolism,
  • providing toxic effects.

For example, phytate can bind to important minerals like calcium, zinc, and iron, reducing their bioavailability. Protease inhibitors found in soybean meal can inhibit digestive enzymes and impair protein digestion.

While ANFs can pose challenges, many of them can be deactivated or have their impacts reduced through proper processing techniques.

For example, phytate levels can be reduced through soaking, germination, or fermentation of grains and oilseeds. Heat treatment through processes like extrusion can also help deactivate ANFs.

Being aware of the presence of ANFs and taking steps to counteract them allows animal nutritionists to safely utilize feed ingredients that would otherwise contain too high of levels.

Antinutritional Factors in Feed Ingredients

As a livestock feed manufacturer, having a good formulation is not enough to feed the targeted animal quality feed, a good knowledge of the antinutritional factor will aid the inclusion level of every ingredient you want to add.

I have compiled the most common antinutritional factors you can find in most animal feed ingredients. They are:

1) Phytate

Phytate is an anti-nutritional factor found in many plant sources like grains, legumes, nuts, and seeds. It contains phosphorus tightly bound to phytic acid, which makes it poorly absorbable by monogastric animals like pigs and poultry.

The phytic acid binds to important minerals like iron, zinc, calcium, and magnesium, forming insoluble salts that pass through the digestive system without being absorbed. This can lead to mineral deficiencies if high-phytate ingredients make up a major part of the diet.

There are several ways phytate can be reduced in feed ingredients. Soaking, germination, and fermentation using phytase enzymes or microorganisms can degrade up to 90% of the phytic acid in grains, legumes, and oilseeds.

Adding supplementary phytase is another common method, which breaks the phosphate bonds in the phytate inside the digestive tract to increase mineral absorption. Proper processing techniques allow high-phytate feeds to be utilized effectively in animal diets while mitigating anti-nutritional effects.

2) Glucosinolates

Glucosinolates are a class of toxic secondary plant metabolites that contain sulfur and nitrogen primarily found in brassica crops like canola. Glucosinolates have negative impacts on the utilization of protein, minerals, and nutrients in animal feed.

The issue is their breakdown products like isothiocyanates, which interfere with iodine uptake and impair thyroid function. Unprocessed glucosinolates and their metabolites can lead to reduced feed intake, decreased weight gain, thyroid enlargement, and even reproductive issues in livestock.

To reduce the negative effects of glucosinolates, brassica seeds, and oilseed meals are carefully heat processed. Processing techniques like expanding, extruding, and toasting use controlled time and temperature to inactivate myrosinase, the enzyme that breaks down glucosinolates into toxic compounds.

This improves the nutritional value and utilization of canola and other brassica crops as animal feed ingredients. Properly processed canola meal can be a rich source of protein in swine, poultry, and cattle diets.

With careful thermal treatment, the anti-nutritional factors in brassica crops can be deactivated to render them safe and beneficial animal feed ingredients.

3) Saponins

Saponins are bitter compounds found in many feeds like soybeans, alfalfa, and other legumes and grains. They irritate the intestinal mucosa and have a bitter taste that can reduce palatability and feed intake in animals.

Common processing methods used to remove or deactivate saponins include:

  • Extraction: Liquid extraction using alcohol removes undesirable saponins from soybeans and other beans.
  • Heat treatment: Cooking and expanding feed ingredients deactivates saponins.
  • Fermentation: Microbial fermentation helps break down saponins.

Saponins exhibit anti-nutritional effects when present in animal feeds. Proper processing via extraction, heating, and fermentation helps reduce saponins to safe levels for improved animal performance.

4) Tannins 

Tannins are the most common antinutrient in livestock feed ingredients; they are water-soluble polyphenols. Tannins are found in many plant foods, including legumes, cereals like sorghum grain, and many fruits.

Tannins have protein-binding properties and can inhibit the digestion of protein and the absorption of vitamins and minerals. This is why tannins are considered anti-nutritional factors when present in animal feeds.

Sorghum contains the highest percentage of tannins; before including sorghum in livestock feed formula, most especially monogastric animal feed, I advise nutritionists to treat sorghum for tannins.

There are a few ways that tannins in feed ingredients can be treated to reduce their anti-nutritional effects, these are:

-Soaking: Soaking legumes, grains, or other tannin-containing ingredients in water can help to leach out some of the tannins.

– Heating or Boiling: Heat treatments are effective at deactivating tannins. Boiling ingredients high in tannins can help break down some of these compounds.

– Alkali treatment: Treating high-tannin feedstuffs with an alkaline solution helps to neutralize tannins. Adding an alkali like sodium bicarbonate to the soaking water is commonly used.

Although tannins have some benefits, like antioxidant effects, their protein binding properties mean they need to be treated in animal feed ingredients through soaking, heating, or alkali treatments to limit anti-nutritional effects.

) Lectins

Lectins are anti-nutritional factors found in grains, legumes, and certain other feed ingredients. Lectins act by disrupting nutrient absorption in the small intestine by binding to the intestinal epithelial cells. This prevents optimal absorption of nutrients like proteins, starches, and minerals.

Some common ways that lectins are treated or reduced in animal feeds include:

– Soaking: Soaking grains, beans, or legumes in water can help to reduce lectin content. The water leeches out some of the lectins.

– Heating or cooking: Proper heating and cooking of feed ingredients like soybeans can denature lectins and reduce their anti-nutritional effects. Roasting, extrusion, and other heat processing methods are used.

– Germination: Allowing seeds or grains to germinate encourages plant enzymes to start breaking down lectins and other anti-nutrients. Germination is used on feed grains like barley.

Proper treatment of ingredients through the aforementioned means can help to reduce the lectin content and allow targeted animals to benefit from the nutritional value of grains and legumes in feeds.

6) Protease inhibitors

The most common antinutritional factors present in protein sources in livestock feed are Protease inhibitors; they are found in soybeans, legumes, cereals, and other plant sources that inhibit digestive proteases and enzymes.

Soybeans contain particularly high levels of protease inhibitors. Protease inhibitors bind to digestive enzymes and prevent them from breaking down proteins into amino acids. This reduces protein digestibility and absorption.

The main protease inhibitors found in plant feedstuffs are trypsin inhibitors, chymotrypsin inhibitors, aminopeptidase inhibitors, and carboxypeptidase inhibitors. These antinutritional factors can negatively affect growth performance and feed efficiency in livestock animals.

Protease inhibitors are heat labile. Processing techniques like extrusion, expansion, and toasting can denature and inactivate protease inhibitors in soybean meal and other feed ingredients. The trypsin inhibitor activity in soybean meal is reduced by around 85% after heat processing.

Careful heat treatment is important to remove protease inhibitors while avoiding overheating that could damage amino acids. Processed soybean meal contains sufficiently reduced protease inhibitors for livestock feed.

7) Non-Starch Polysaccharides

Non-starch polysaccharides (NSPs) are carbohydrates found in grains like wheat, rye, and barley; they are indigestible by monogastric animals like poultry and swine. The main NSPs of concern are arabinoxylans, cellulose, and beta-glucans.

NSPs increase digesta viscosity, limit nutrient digestibility, and reduce performance. They have antinutritional effects by:

  • Increasing digesta viscosity and slowing digestion
  • Trapping nutrients like proteins, starch, lipids, making them unavailable for digestion
  • Altering microbial fermentation in the gut
  • Irritating the intestinal mucosa

To counteract the negative impacts of NSPs, exogenous enzymes like xylanase, beta-glucanase, and cellulase are added to the monogastric animal diets. This supplementation helps break down NSPs and improve nutrient utilization by the animals.

Also, processing techniques like pelleting and extrusion cooking help rupture cell walls, decreasing the antinutritional effects of NSPs. Applying heat and pressure makes nutrients more accessible for enzymatic breakdown and absorption in the gut of the fed animals.

These treatment options allow NSP-rich grains to be effectively utilized in monogastric animal diets. NSPs have no detrimental effect on ruminant diet. The complex stomach of ruminant animals aids the breakdown of these antinutrients.

8) Mycotoxins 

Mycotoxins are toxic, carcinogenic metabolites produced by molds that can grow on crops and grains used in animal feed.

The most concerning mycotoxins are aflatoxins, ochratoxins, fumonisins, trichothecenes, and zearalenone. Even small amounts of these mycotoxins can negatively impact animal health and performance.

For effective control of mycotoxin contamination in animal feed, you must carry out proper post-harvest crop management such as:

-Careful monitoring of temperature, moisture levels, and storage times helps limit mold growth and mycotoxin production pre-harvest and during storage.

-Testing of grain and feed ingredients is also important to identify any unsafe mycotoxin levels so contaminated batches can be diverted from animal feed.

-Regulatory limits help control the maximum permissible amounts of key mycotoxins in animal feeds in many countries.

In addition to post-harvest management, physical, chemical, and biological treatment methods can also help decontaminate feed and reduce mycotoxin content. These include grain cleaning, various chemical treatments, irradiation, binding agents, and enzymatic detoxification.

However, the most effective strategy is preventing mycotoxin contamination in the first place through agricultural and storage best practices. Mycotoxin risks must be carefully managed to ensure animal health and performance.

9) Gossypol

This is commonly found in cotton seeds,  cotton seed meal is used as a protein source in animal feed. Gossypol is a yellow pigment and a polyphenolic aldehyde which is an antioxidant and polymerization inhibitor. It is toxic to monogastric animals like poultry.

The gossypol can be eliminated during processing. The shearing effect of the screw press in the expeller is an efficient gossypol inactivator. Also, treatment with ferrous sulfate can ameliorate the effects of gossypol with doses ranging from 1 to 4 parts ferrous to 1 part of gossypol.

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End Notes

I hope this article solves problems related to anti-nutritional factors and the safe use of animal feed ingredients. Share this article and feel free to ask any question in the comment section.

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