Biology

Proteins are vital elements in animal cells. In the process of digestion, proteins are broken down into amino acids with the use of enzymes such as proteases. These amino acids supply the nitrogen nutritional requirements of the animal body (Cliff Notes). There are two types of amino acids the essential and non-essential. Essential amino acids cannot be produced by the animals internally, while non-essential amino acids can be produced by the animals with other nitrogen sources. A total of twenty amino acids are found in the body with ten of these as essential amino acids and therefore must be included in the diet.

The biologic value of proteins is related to the essential amino acid requirements of the animal. It is also related to the rate of metabolism and digestion of the animal. Biologic value of protein is inversely proportional to the protein requirement in animal diets for the supplementation of amino acids (Merck Veterinary Manual).  Complete nutritional requirement of protein is attained when the metabolic need for amino acids and nitrogen is fulfilled.  Dietary proteins used for growth and maintenance of animal bodily functions are inefficiently converted to energy when there is insufficient energy from dietary fats and carbohydrates. Improper protein to calorie ratio is likely to cause protein deficiency in animals.

Protein requirements differ with species, digestion, age, health and environment. They are expressed as a percentage of diet or as protein-energy ratio.  Protein requirements decrease as animals age. The utilization of proteins is also different in ruminant and non-ruminant animals. This is because of their diet and energy requirements. Animal feeds vary in their protein content depending on the type of animal being fed. Without proper nutrition, nutrition deficiencies and diseases may cause death to the animals.

Ruminants such as cattle and sheep have the ability to synthesize proteins from simple nitrogen compounds with the use of rumen microorganisms. These microorganisms are able to transform nitrogen from urea into amino acids and proteins into meat and milk. Sufficient nitrogen and rumen degradable protein must be provided to increase bacterial fermentation, energy digestibility and feed intake. The number of microbes depends on the available protein of the feed. If the microbial population is high, then there is greater use of the feed by the ruminant for its needs. Available energy is required to increase ruminant microbial protein synthesis. Regular adequate amounts of protein must be supplied to maintain good productivity of the ruminant and the rumen microbes (Beeflinks.com).

Two types of protein are needed by cattle in their diet. Rumen degradable protein is the protein degraded by the rumen microorganisms, while the rumen undegradable protein or bypass protein is the protein that heads straight to the stomach of the ruminant for digestion. Ruminants are required about 65 to 68 percent of the protein to be rumen degradable for efficient rumen function. Degraded protein not absorbed as ammonia are excreted out as urine and considered as a waste of protein. Bypass proteins or rumen undegradable proteins are believed by researchers contain essential amino acids that are not available in rumen degradable proteins. This factor is important for high-producing livestock.

An advantage of ruminant nutrition is during emergency situations, ruminants can survive on minimal amounts of proteins by reusing the available urea in the rumen. Another advantage is the feed is maximized by the rumen microbes and more protein is being produced from the diet.  Ruminant nutrition is also not particularly concerned with the amino acid composition of the dietary protein (Khan).

Successful nutrition of monogastric or single stomach animals is essentially concerned with proteins of suitable biological or nutritional value. Like in ruminants, proteins cannot be stored in the body unlike fats and carbohydrates. Therefore, meeting the protein requirements for animals is important. Proteins required in feeding monogastric animals comprise of different and specific essential amino acids depending on the animals energy requirements.

In pig production, about one-third of the protein used as body protein, and less than a fifth is available in the edible parts of the pig. The 10 dietary essential amino acids needed in pig nutrition are arginine, histidine, isoleucie, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Cystine and tyrosine can meet a portion of the requirement for methionine and phenylalanine, respectively (Merck Veterinary Manual).

Protein and energy in diet is directly proportional in pigs. The amount and composition of amino acids in diets of pigs depends upon their feed intake and digestible energy. Diets with low protein contents are at a greater risk of protein imbalance, while incorrect amino acid composition in the diet decreases productivity. In an ideal protein, pig feed must contain a constant proportion of essential amino acids while the amount can differ according to the age, sex, breed and environment of the animal.

Amino acidenergy ratio has been known to have interactions with the climate.  Low energy diets are required for pigs in warm climates, while high energy diets are needed for pigs in temperate climates. This is the reason for maintaining the proper protein and essential amino acid ratio (Prez).

The non-essential amino acids of cats are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and specifically taurine. Taurine is the most important amino acid in the cats nutrition. This amino acid is essential for growth. Limited taurine supplementation can cause irreverisble degeneration of the retina and eventual blindness and dilated cardiomyopathy (Readers Digest Association (Canada) Ltd 157-8). All unwanted nutrition from excessive amino acid supplementation is still absorbed into the body which in turn causes cat obesity. Kittens have a recommended protein of 30 while adult cats are required 25-30 protein in their diets (Pet Education.com).

Cats are naturally obligate carnivores which mean that they need anima-based proteins in their diet. As carnivores, cats have poor enzyme activities and cannot degrade plant proteins compared to animal proteins. This inability of cats will forcefully break down other body protein tissues in limited exogenous proteins supplementation (Pierson).

Proteins in dogs are significant in the development of bone, muscle, blood, tissues, hormones, enzymes and immunity. Dogs have the same amino acid composition as cats except for taurine. Puppies have 28 recommended protein, while adult dogs have 18. Performance, racing sled and lactating dogs need 25, 35 and 28 recommended proteins, respectively (Pet Education.com). Not all proteins have equal amino acid compositions. Proteins vary in the level of digestibility and usability as nutrients. An example of such is that leather is mainly protein but has zero digestibility for dogs as a food source. Meanwhile, corn has high digestibility as a carbohydrate source but only has a small percentage of protein that a dog requires. Dogs are able to consume two types of proteins. Incomplete proteins are plant-based proteins such as grains and vegetables. Complete proteins are animal-based proteins such as meat, eggs, and fish. Protein requirements vary with dogs depending on how much of the essential amino acids are supplemented by that protein. Young, extremely active or pregnant requires more proteins because of the high energy requirement of such dogs. Excess protein supplementation is converted into energy in dogs.

Proteins are the body builders of the animal body. Such proteins are digested to form amino acids required in the digestion and metabolism of animals. Essential amino acids and non-essential amino acids supply nitrogen to the body. Essential amino acids are required in the diet of animals depending on their specific needs.  Ruminants have two types of proteins that are digested in the body. Rumen microorganisms digest rumen degradable proteins, while rumen undegradable proteins are digested directly into the stomach. In non-ruminants, amino acid amount and composition is specific according to the species, lifestyle, environment and health status. Amino acid deficiency can cause a number of illnesses that may cause death to the animals. Proteins are essential in the growth, maintenance and good functioning of the animal body.