Evaluation of foods as sources of nitrogen and amino acids.
نویسنده
چکیده
In any managed system of animal production the problem is to match the nutrient requirement of the animal with a supply of the nutrient in the feed to achieve the maximum economic return. Any matching system has one major prerequisite : the nutrient requirement and nutrient content of feedstuffs must be expressed in the same units. The manner in which this matching is carried out may differ according to the metabolism of the nutrient. The Agricultural Research Council (1965) calculations with respect to minerals and energy are examples of two different methods. The current method of expressing protein requirements for ruminants is as digestible crude protein (DCP). The requirement values have been determined by the trial and error approach of feeding increasing levels of DCP and determining the point of maximum response. For some considerable time the imperfections of the method have been apparent. Many experiments have shown that diets with equivalent DCP content do not necessarily sustain the same productivity. Balch (1967) has drawn attention to the very significant interaction that exists between protein and energy in determining the response of the animal. Even under isoenergetic, isonitrogenous conditions it is quite easy to demonstrate differences in animal productivity between different types of protein as supplements to a concentrate (Whitelaw, Preston & Dawson, 1961) or roughage basal diet (El-Shady, 1958; Little, Burroughs & Woods, 1963). Furthermore the relative values of the supplements are not necessarily the same under conditions where either the supply of amino acids to the small intestine or the supply of nitrogen to the rumen microorganisms is the limiting factor. T h e need for a new system of protein evaluation of animal feeds is becoming more imperative with changes in feed technology. Screw pressing, solvent extraction, drying, heating, grinding and pelleting of feeds have all been shown to affect the solubility of the protein, the rate of passagc through the rumen arid the site of digestion of the protein (Coelho da Silva, Seeley, Beever, Prescott & Armstrong,
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عنوان ژورنال:
- The Proceedings of the Nutrition Society
دوره 32 2 شماره
صفحات -
تاریخ انتشار 1973