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Clemson University, Clemson, South Carolina2
Abstract
Although progress has been made in understanding the biochemical and physiological mechanisms involved in the utilization of non-protein nitrogen, problem areas still exist.
Obtaining comparable rates of urea hydrolysis and of fixation of liberated ammonia into cellular protein remains a major factor limiting the efficent use of urea nitrogen. To overcome this problem, it will be necessary to increase the quantity of dietary constitutents synthesized into microbial cells in the rumen and to decrease the ureolytic activity of the rumen mocroorganisms. The thermodynamic limitations imposed by the anaerobic nature of the rumen warrant greater consideration in future investigations.
Realization of the importance of protein quality in the nutrition of ruminant animals represents a key advance in our knowledge. As recent research suggests, inability of the rumen microorganisms to synthesize sufficient quantities of all amino acids needed to prevent deficiencies or imbalances may be a major factor responsible for the lowered animal performance obtained with urea diets. Individual microbial species, as well as total bacterial and protozoal protein fractions, are, no doubt, complimentary in nutritive value. Although studies on the amino acid nutrition of ruminant animals presents many problems not encountered with non-ruminant animals, the energetic investigator will find this a rewarding research endeavor.
Clarifying the magnitude of the urea-recycling mechanisms under various dietary conditions and elucidating specific tissues involved in the adaptation response are paramount to effective utilization of urea.
If ruminant animals are to continue to be an integral link in the human food chain, full advantage must be taken of the inherent physiological and biochemical capabilities which mammalian species with less advanced digestive systems do not possess. From an economic viewpoint, it is important not only to use non-protein rather than protein nitrogen sources but also to derive a considerable portion of dietary carbohydrate from sources that cannot be used directly by man. The successful utilization of nonprotein nitrogen in conjunction with forages and residual carbohydrates, which are presently either discarded as waste or disposed of at additional cost, is thus dictated. Utilization of urea with corn silage demonstrates the feasibility of combining two of the attributes of ruminal metabolism. Development of new forage species with increased amounts of available carbohydrates and of improved technology to increase carbohydrate availability of waste products is necessary if nonprotein nitrogen and energy sources unusable by man are to be routinely used in ruminant feeding. If recent scientific advances are interpreted as an index of our capabilities, such a suggestion is not unrealistic.
1 Invited paper presented at a joint session of the Southern Section, A.S.A.S. and Southern Division, A.D.S.A., January 31, 1967, New Orleans, Louisiana.
2 Department of Dairy Science. Technical Contribution No. 638, South Carolina Agricultural Experiment Station. Published by permission of the directors.
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  F. H. M. Chizzotti, O. G. Pereira, L. O. Tedeschi, S. C. Valadares Filho, M. L. Chizzotti, M. I. Leao, and D. H. Pereira Effects of dietary nonprotein nitrogen on performance, digestibility, ruminal characteristics, and microbial efficiency in crossbred steers J Anim Sci, May 1, 2008; 86(5): 1173 - 1181. [Abstract] [Full Text] [PDF]
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