Protein Sources in Animal Nutrition: Uses and Trends

Production animals need to be nourished with balanced nutrition to achieve proper development levels. Feed (or nutrition) is the most expensive part of the production, accounting for approximately 70% of operation costs, with protein being the fraction with the highest value in a feed. Studies indicate that 33,3% of this cost is from protein.

Chemically speaking, proteins are amino acid condensations made through peptide bonds. When a certain food that contains this component is ingested, it is hydrolyzed in the digestive system into peptides and free amino acids. These are then absorbed by the body and metabolized to form new types of proteins in different body tissues, such as muscles, and functional proteins, such as enzymes. Amino acids are subdivided into non-essential and essential amino acids — the latter needing to be supplied through the diet.

Because it is a crucial component in feed production, zootechnicians or animal feed formulators (or both) look for ingredients with high protein content and an appropriate balance of amino acids at lower costs. With these conditions, research and development departments can present solutions for new protein sources that meet the needs mentioned earlier. Balanced nutrition provides proper and healthy growth for production animals. Therefore, using high-quality ingredients will ensure that the farmed animal can maintain its health despite the challenges and stress inherent to intensive animal production.

The use of new protein sources, such as hydrolyzed proteins, allows the production animal to achieve its maximum zootechnical performance. They also deliver specific functionalities, such as antioxidant, antimicrobial, antifungal, antiviral e antiparasitic activities.

The Brazilian agro-industry produces several protein sources. Soybean crushers are one of the examples, as they are suppliers of soybean meal-derived proteins. Another example is the meatpacking industry as it supplies proteins obtained from the processing of carcasses or viscera derived from butchery. In the following sections, new sources of proteins that present high amino acid availability and digestibility will be discussed.

Plant-based Proteins

There are several sources of plant-based protein, and the main ones are soybean, sunflower, canola, wheat and others.

Usually, plant-based proteins are characterized by an imbalance of amino acids and high levels of anti-nutritional factors — such as indigestible non-starchy polysaccharides, phytic acid, tannins and alkaloids, which affect the use of this nutrient in animal nutrition formulations. To circumvent this situation, techniques that can release these proteins and deactivate anti-nutritional factors are used, such as the inactivation of soybean (trypsin inhibitors) and the use of phytases to deactivate phytates.

Due to the wide diffusion, in this first article, we are going to discuss soy and a few of its by-products.

Soy

Soy (Glycine max (L.) Merr.) is one of the most important legumes (grains contained in pods) in the world, with America representing approximately 80% of the world production, while Brazil is responsible for 50% of the world trade of this legume.

Soy is extensively produced because it is rich in high-quality proteins while also yielding edible oil. These derivatives have high nutritional value with pleasant sensory characteristics. Due to the benefits previously mentioned, derivatives are widely used as feed ingredients.

The most used source of plant-based protein in the world is soy, and, as a result, there is a lot of research in development regarding this important raw material. One of the many products made from this legume is Soy Protein Concentrate (SPC), which has been marketed since the 1950s and is mainly used to obtain a high concentration of proteins (minimum 70%) in products intended for animal nutrition, with the added benefit of not presenting anti-nutritional components.

Soy derivatives display important characteristics in the production of animal nutrition, such as:

• The spatial arrangement of its peptides, which provide intermolecular interactions with other proteins and components of the food matrix, improving gelatinization and paste formation
• Hydrophilic properties, enabling solubility, adhesiveness and viscosity suitable to the products.

Soybean Meal

One of the most important soy derivatives for animal nutrition is Soybean Meal. The production of this derivative is possible due to the extraction of soybean oil. Until the mid-1930s13, the meal was not extensively used by zootechnicians/nutritionists. However, over the years, numerous researches have been carried out on farm animals (swine, cattle, poultry, etc.) to reveal the potential of this valuable ingredient.

Nowadays, research on this ingredient is focused on:

• The digestibility of amino acids
• Anti-nutritional factors
• Metabolizable energy and net energy.

When compared to other plant-based protein sources, soybean meal is shown to have less nutrient variability and lower concentrations of anti-nutritional factors.

Generally, it is sold in different concentrations of crude protein, ranging from 40% to 48%, and this concentration is adjusted by the inclusion of other by-products, such as soy hull.

Proteins of Animal Origin

The animal proteins present in meals derive from materials processed by meatpackers that would be discarded and cannot be commercialized for human consumption. The most used animal protein sources in nutrition are listed below:

Meat and Bone Meal

This type of meal is produced in independent rendering plants or meatpackers and is composed of animal bones and tissues from cattle, swine and sheep butchery. It is both a source of protein and a source of important minerals, such as calcium and phosphorus.

Meat and Bone Meal presents a high variation in its composition because there is no standard in the proportion between bones and meat tissues. The amount of protein is inversely proportional to the mineral content, meaning: high mineral content leads to low protein content. Usually, it is commercialized considering its crude protein concentration, being 35, 40, 45 and 55%.

Feather Meal

The defeathering of poultry in meatpackers results in a by-product with high protein content. When this by-product is submitted to a pressure-cooking process it is called hydrolyzed feather meal, and it contains 78 to 92% crude protein, of which 85 to 95% is keratin.

According to Nascimento et al. (2002), this raw material does not present satisfactory digestibility. This characteristic is attributed to the hydrogen bonds and intramolecular hydrophobic interactions in the keratin molecule. To improve its digestibility, this ingredient can go through enzymatic processes that release peptides, thus becoming an ingredient with better quality.

Poultry Meal

According to Padilha (2005), poultry processing yields by-products such as heads, viscera, blood, fat, skin, bones and substandard carcasses. These are then transformed into viscera meal.

Poultry Viscera Meal is an ingredient with high protein content, with crude protein ranging from 55 to 70%, depending on the concentration of bones in the components included in the cooking process.

The digestibility of this protein suffers interference in its values due to the production process (cooking) and the inclusion of other raw materials with different digestibility rates in the process.

Concerning this ingredient, methods are constantly being developed, such as hydrolysis — capable of improving the digestibility of this ingredient and guaranteeing the performance of feeds produced with it.

Trends in the Use of Processed Proteins in Animal Feeds

Choosing ingredients of excellent quality is essential to improve the quality of feeds. In light of this, research is ensuing to discover new processes, such as the enzymatic hydrolysis that produces functional peptides, to deliver maximum performance from the components and generate new ingredients.

Consequently, with new technologies used to process food and the pursuit of alternative protein sources, new ingredients emerge as options to meet the nutritional and functional needs of animals. In sequence, some alternatives are highlighted.

Functional Peptides

Peptides are defines as short sequences of food proteins, composed mainly of 2 to 20 amino acid residues condensed in a molecule. They are obtained through the processes of digestion or fermentation or both of intact proteins.

These peptides have positive physiological effects, implying they are functional ingredients or bioactive molecules. They aim at various targets, such as the immune, cardiovascular, digestive and endocrine systems, indicating they can improve animal performance.

Although there is still a long way to go to understand the mechanisms of action of these functional peptides in organisms, what has already been discovered indicates that it benefits the organism that regularly ingests these molecules. Therefore, the zootechnician or the feed formulator (or both) should encourage the inclusion of these ingredients in their formulations.

Chicken Protein Hydrolysate

Broil by-products, such as viscera and offal of low commercial value, go through an enzymatic process that releases amino acids and low molecular weight peptides. When the ingredients are used for animal nutrition, they are easily absorbed. According to dos Santos Cardoso, et al. (2020) this ingredient has a high protein content (above 75%), it presents a balanced amino acid profile and has high palatability for Nile Tilapia. Therefore, when this ingredient is used in animal nutrition, it improves the zootechnical performance of fish.

Chicken Protein Hydrolysate (CPH) is a functional protein specially formulated to improve the performance of animal feeds. Produced through an enzymatic hydrolysis process that generates smaller chains of bioactive peptides and amino acids, it forms a functional ingredient with high biological value and digestibility. CPH offers animals benefits like high digestibility, high attractiveness and palatability, and high protein content with a balanced amino acid profile.

The analysis of the profile of amino acids found in organisms, tissues and cells (HERRERO et al., 2008) found 78 bioactive peptides in Chicken Protein Hydrolysate. The main peptides identified were: anti-amnestic, antioxidant, antithrombotic, angiotensin (ACE) inhibitor, dipeptidyl peptidase-4(DPP4) inhibitor, regulatory, insulin secretion inhibitor, neuropeptide, chemostatic, stomach membrane regulator, phosphoinositol metabolism regulator and immunostimulant peptides. In general, CPH is an ingredient source of bioactive peptides, which improves the metabolism and health of animals while also being a hypoallergenic source.

Feather Enzymatic Hydrolysate

Conventional hydrolyzed feather meal does not present satisfactory digestibility due to hydrogen bonds and intramolecular hydrophobic interactions in protein molecules. A proteolytic process is performed to solve this problem, breaking peptide bonds regardless of the size of the keratin peptide chain.

As it is produced from feathers, this ingredient has a very high protein content (above 75%), with the excellent feature of containing essential amino acids in its composition — especially leucine, phenylalanine and tryptophan.

Insect Meal

Some studies claim that insect meals have great potential in animal nutrition, becoming a trend in this branch of the animal feed industry. Insect meal (Tenebrio molitor) has approximately 45 to 65% protein, thus being an excellent protein source while having an adequate amino acid profile.

Research has demonstrated the feasibility of total or partial replacement of traditional protein sources by insect meal in poultry and swine feeding. Many authors describe similar or better growth rates when compared to soybean meal, whole fish meal or their combination. Nutrient digestibility can be optimized when combining fishmeal and insect meal in a formulation.

Other Alternative Sources

Some alternatives to using soybean meal as the main protein source are already being tested in swine nutrition. A few alternative plant-based sources have already demonstrated the ability to replace about 50 to 75% of the protein from soybean meal. Cottonseed, de-oiled rice and sunflower bran, and the seeds of some legumes, such as pigeon pea, are some examples.

Yeasts, other than being used as food additives, are alternative protein microorganisms for animal nutrition, and their use as enrichment for feeds is a positive trend in this market. The need to use the by-product of the alcohol industry stimulated numerous researches that discovered the nutritional and nutraceutical potential of these microorganisms, which led them to be researched and incorporated into animal nutrition.

Another alternative food that has already displayed excellent results is bee pollen, which has 10 to 40% protein in its composition. As a food extremely rich in essential amino acids, it demonstrated excellent productive results in studies for broilers, tilapia performance, rabbit reproductive performance, and others.

Conclusion

Every day, animal nutrition has, in its scope of raw materials, new sources of proteins obtained from studies conducted by research and development teams, combining balanced nutritional composition and excellent functional properties.

Therefore, it is understood that the use of new sources of proteins has increased and become essential in the animal nutrition market. In addition, processed proteins have stood out as alternatives to add value to meatpacking by-products.

The use of enzymatic hydrolysis to obtain protein hydrolysates rich in bioactive peptides and an adequate balance of amino acids is a process that is on the rise. Hydrolyzed proteins from by-products of the meatpacking industry are alternative sources of functional protein with high biological value since they are an excellent source of bioactive peptides, thus improving the performance, health and welfare of animals.