Dietary protein and it’s use for animal production.

Proteins consist of amino acids (AA) joined together by peptide bonds. The structure of a protein is determined by the sequence of the individual amino acids it has in the polypeptide chain. This is also called the primary structure of the protein.

Physiological role of proteins

Proteins are essential for life and are the major structural components of animal tissues (e.g., skin, muscles, wool, feather, tendons, eggs). Additionally, proteins are involved in biochemical (e.g., enzymes), immunological (e.g., immunoglobulins), transportation (e.g., lipoproteins),-and other regulatory (e.g., hormones) activities. Furthermore, proteins can serve as an energy source, when required. The AA’s (also called ‘building blocks of life) needed to build these proteins should be provided through nutrition. Ruminants, however, obtain part of their AA’s differently: their digestive tract microbiota can synthesize proteins from nonprotein sources. Young calves are not ruminating yet and depend, just like the monogastrics, for their AA’s supply on nutrition.

Protein requirements in animals

Protein requirements vary with the different production phases of animals. Diets with higher protein levels are therefore used in young animals and during pregnancy and lactation. There are over 300 different AA’s known to us. Twenty of them are important components of animal proteins (muscles, connective tissues, skin, feathers, horns, blood, enzymes, and hormones). Only 10 amino acids should always be present in the diet of animals as they cannot synthesize them orat least not in sufficient amounts; these are called essential amino acids. Not only should they be present in the feed but also in the right amount and relative quantity. If the balance between, at least, the essential AA’s is off, the AA’s in excess will be excreted.

When using low protein diets there is a minimum of crude protein from the feed which must be observed. If protein is supplied below the minimum will not be enough building blocks to maintain the balance of the non-essential AA’s

Protein digestion

Protein digestion starts in the stomach where the presence of feed leads to the secretion of pepsinogen by cells from the gastric mucosa. Pepsinogen is activated to form pepsin (active form) through acid (HCl) produced by other cells from the gastric mucosa. Pepsin, is a protease (protein degrading enzyme) and starts the breakdown of protein into AA’s. This enzyme splits the feed protein molecules into peptides of various sizes. Once these enter the small intestine, other proteases like trypsin and chymotrypsin brake down the peptides into 20 individual AA’s. See table . Young animals may produce a substance called rennin (milk-coagulating agent) that facilitates the protein transport into the small intestine.

In this part of the digestive tract peptide structures are broken down to single AA’s with the help of various digestive enzymes. Absorption of the AA’s is facilitated by the villi within the small intestine into the bloodstream. Free amino acids are the major form for absorption into the circulatory system. However, some di-, tri-, and oligopeptides are also absorbed. Once absorbed the amino acids can be used for tissue protein, enzyme, and hormone synthesis and deamination or transamination, and the carbon skeleton can be used for energy.

Excess AA’s

Amino acids can only be absorbed in the small intestine. Amino acids or peptides leaving the small intestine are lost to the animal as they cannot be absorbed in the large intestine but are fermented by the microbiota instead. This results in the production of ammonia, NH4 and leads to increased urea (mammals) or uric acid (birds) excretion. The excretion of urea/uric acid is an energy consuming process, so any excess NH4⁺ and AA’s have a negative impact on the energy utilisation by the animal. A large proportion of the microbiota that is capable of protein fermentation in the large intestines is considered pathogenic and the risk of enteritis / diarrhoea increases when more AA’s are passing on to the large intestine.

Digestibility of AA’s

To evaluate protein sources for animal feed not only its composition in AA’s is of importance, but also the standardized ileal digestibility (SID) is taken into consideration. The SID measures the difference between the amount of amino acids ingested, the amount of amino acids recovered from the digesta in the ileum, and the basal endogenous amino acid losses. SID can differ between protein sources and is affected by age of the animal with increasing SID values for older animals. Health status also has proven to have a large influence on SID values as activation of the immune system comes at a nutritional cost. Furthermore, the presence of anti-nutritional factors (ANF’s) in certain protein sources can reduce the SID.

Anti-Nutritional factors

Anti-nutritional factors are all substances that interfere with the utilization of dietary nutrients. These factors are collectively defined as antinutritional factors (ANF’s) and are harmful to gut physiology and morphology and, subsequently, intestinal functionality and consequently lead to reduced utilization of nutrients and consequently depresses animal growth / performance. Protein digestibility can be affected by various ANF’s (trypsin and chymotrypsin inhibitors, lectins, polyphenolic compounds and saponins) and by antigenic proteins that activate the immune system (i.e. beta-conglycinin ). ANF’s can directly cause inflammation and damage in the gut. The intestinal wall is damaged and the barrier between the intestine and the bloodstream falls away leaving a port of entry for pathogens and toxins to enter the body. Another sort of ANF comes from the nitrogen (N) not part of protein (NPN) like urea. This N ca be used by microbiota in the stomach of ruminants to synthesize protein but is NPN will, like undigested N form proteins, become a substrate for the microbiota in the large intestine (this also favours growth of certain pathogens like Lawsonia intracellularis in swine).

Reducing Anti nutritional factors in protein sources

ANF’s can be divided in two general groups after heat processing i.e. those that are heat-labile and those that are heat-stable. Therefore, not all ANF’s are inactivated due to moderate heat and additional treatments is needed to fully reduce the negative effects of ANF’s in animals. An efficient methodology to be used in combination with heat is state-of-the art enzymatic treatment to fully inactivate soy ANF’s. Use of specific enzymes avoid the need for high and extended use of heat resulting in soy protein ingredient that allow young animals to explore the full energetic and nutrient potential. This is called ‘Enzymatically Processed Soy Bean Meal’ è HP300

HP 300 is the ideal protein source for (young) animal diets

As it has a low content of ALL of the ANF’s previously described. HP 300 is physically available/open for digestion due to processing (as opposed to SPC which is gritty and hydrophobic due to alcohol treatment).

HP 300 features consistently the highest SID among the available premium protein sources. Since it does not affect feed intake in any negative way and is low in CFU (< 10.000 CFU / g product ), so there is no upper limit to inclusion.

Table 1. Amino Acids