Amino Acids are the building blocks of the body. Besides building cells and repairing tissue, they form antibodies to combat invading bacteria and viruses: they are part of the enzyme and hormonal system; they build RNA and DNA; they carry oxygen through the body and participate in muscle activity. When protein is broken down by digestion, the result is amino acids. These amino acids are considered “essential” or “non-essential” depending on whether they need to be provided in the diet.
Essential and Non-Essential
There are 22 amino acids that animals need. Animals can synthesize 12 of them. The remaining ones must be consumed. The ones that the animals cannot synthesize are called essential amino acids. They are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and in cats, taurine. Dogs can synthesize taurine, and therefore, it is not supplemented in their food. This is why there is the old adage that dogs can eat cat food but cats cannot eat dog food. A deficiency in any of the amino acids can cause health-related problems.
Amino Acids and Protein Value
Every protein source contains different levels of amino acids and each protein is different in its ability to be broken down into amino acids. So not all proteins are created equal. Some are better for pets than others. The ability of a protein to be used by the body and its amount of usable amino acids is summarized as protein quality (biological value). Egg has the highest biological value and sets the standard for which other proteins are judged. Egg has a biological value of 100. Fish meal and milk are close behind with a value of 92. Beef is around 78 and soybean meal is 67. Meat and bone meal and wheat are around 50 and corn is 45. Things like hair and feathers would be very high in protein but would be down at the bottom of the list for biological value. The actual composition of individual proteins as well as the utilization of amino acids is very detailed.
Although digestibility of pet food is a hot topic, without knowing the biological value of a particular protein, digestibility means very little.
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