Animal Feed

Although vegetable protein contains a high concentration of essential amino acids, it does not have a taste appreciated by many humans. When cooked with meat extract, the food's taste is improved, and its nutritive values for food animals are enhanced, thus providing an efficient concentration of essential amino acids that can be used to produce a tasty meat source throughout the world. The worldwide supply of free amino acids to increase the feed efficiency of feedstock has developed into a successful business in recent years.

Table 1 summarizes the limiting amino acids used as feed supplements (1). For grains such as maize, which is fed to both pigs and chickens, the first limiting amino acid is lysine, whereas in protein sources such as rapeseed meal, it is methionine, lysine, or tryptophan. There are three general methods of supplying lysine: adding soybean meal, which contains it in high quantity; adding a larger quantity of poor-quality protein such as corn gluten meal; or adding lysine directly. The first two approaches are more expensive and less economical in view of wasting nitrogen resources, so the direct addition of lysine has been adopted.

An optimal balance of amino acids is attained by adding deficient amino acids and reducing those in excess. When animals are fed corn—soybean meal (Fig. 1), about 2% of the feed protein contents can be saved without affecting the animal's growth response. One hundred kilograms of soybean meal contained in 2 tons of feed can be replaced by 97.5 kg of corn and 2.5 kg of lysine hydrochloride without lowering its nutritional value. When the price of the latter is lower than the former, the use of lysine increases.

Methionine. Fish meal and vegetable defatted meal are important protein sources of feed. The supply of fish meal has continuously decreased and cannot meet the demands for feed. Because of the decrease in fish meal for feed and the increased use of vegetable protein in vegetable oil meal, the demand for methionine has increased.

Lysine. As the demand for vegetable defatted meal has increased and the importance of amino acid balance in protein has been recognized, lysine has received increasing attention. Cereals are considered an energy source and comprise 60 to 80% of assorted feeds; they play an important role as protein sources but contain relatively small amounts of lysine. To compensate for this shortage, lysine has been used in place of fish meal.

When the co-amino group of lysine reacts with a car-bonyl group of a sugar derivative cmpound, which gives a positive Fehling reaction, a Schiff base is formed. These Schiff bases are not used as nutritional compounds. This reaction, which is accelerated by heat treatment, is usually performed to improve the protein efficiency.

Table 1. Limiting Amino Acids of Some Common Feeds for Pigs and Chickens




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