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PAPERBACK list:$33.50 Web:$30.15 add to cart PDF BOOK your price: $26.00 add to cart Rights & Permissions Free Resources PDF EXECUTIVE SUMMARY Display this book on your site! Related Titles Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) Nutrient Requirements of Dairy Cattle: Seventh Revised Edition, 2001 Other Related Titles Ruminant Nitrogen Usage (1985) Board on Agriculture (BOA) Web Search Builder Use this book's key terms to search within this book, across our collection, or across the Web. Skim This Chapter Skim this chapter and use this chapter's key terms to search within this book. Reference Finder Paste in your own text to find books that relate to your topic. Page 1   E-mail  Facebook  Digg  Stumble  Twitter More Page 1 Front Matter (R1-R10) 1 Introduction (1-3) 2 Parameter Names for Describing Protein Metabolism (4-6) 3 Comparison of New Protein Systems for Ruminants (7-22) 4 Feed Evaluation (23-27) 5 Degredation of Dietary Crude Protein in the Reticulo-Rumen (28-36) 6 Microbial Growth (37-45) 7 Digestion and Absorption in the Small Intestine (46-52) 8 Nitrogen and Absorption in the Large Intestine (53-56) 9 Nitrogen Metabolism in Tissues (57-65) 10 Application to Ruminant Feeding (66-74) References (75-86) Appendix Tables (87-136) Index (137-138)

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Introduction The complexity of the digestive process in ruminants is well recognized by all who work with ration balanc- ing in those species. The fact that digestion is a two step process-first by bacteria in the digestive tract and sec- ond by the host animal results in the need to consider two entirely separate but interdependent ecosystems. Nitrogen (protein) nutrition in ruminants is a com- plex, dynamic process. Extensive research has been and is being conducted on various components of the system. Nitrogen (N) is a critical nutrient in the ruminant, since it is a key component in protein (amino acids). The ruminant cannot use nitrogen as a nutrient at the tissue level any more than the alfalfa plant can use atmo- spheric nitrogen without microbial intervention. How- ever, as the nitrogen-fixing bacteria in the alfalfa roots enable atmospheric gaseous nitrogen to be trapped as plant tissue protein, the bacteria in the rumen can cause nonprotein nitrogen (primarily as ammonia) to be trapped as bacterial protein. These bacteria are subse- quently digested by the animal and their protein is used to supply needed amino acids for production of animal protein for deposition in milk, wool, or animal or fetal tissues. Ruminal bacteria in most instances cannot produce enough protein to meet the needs for maximum produc- tion of the animal. In such cases, productivity of the ani- mal depends on the ability of the livestock producer to select those feeds and supplements to maximize bacte- rial production and, if needed, supply protein that will escape digestion in the rumen and pass to the small intes- tine to supply additional amino acids. If production of ammonia in the rumen from the feed sources, such as nonprotein nitrogen or feed protein that is rapidly di- gested, exceeds the capacity of the bacterial population to use ammonia, some of the excess can be lost and high concentrations may be toxic. A portion of bacterial ni- trogen is in the form of nonprotein nitrogen and is of little nutritional value to the animal. Hence, conversion of dietary protein to microbial protein can be wasteful quantitatively and qualitatively. The large intestine is another site of bacterial growth. 1 Unlike bacteria from the rumen, bacteria from the large intestine are excreted by the host without being exposed to the digestive processes in the small intestine, so fer- mentation in the large intestine increases recovery of en- ergy but not nitrogen. In the past, protein requirements for ruminants have been defined in terms of total or digestible nitrogen con- tent of the feed. One unit of feed nitrogen is found in 6.25 units of feed protein. This system ignores the differ- ences that exist among feedstuffs both in the form of ni- trogen in feeds and its fate following ingestion by the animal. This publication will review the biology of nitrogen metabolism in ruminants and outline a method for bal- ancing the diets for ruminants based on these concepts. This method considers that the system is multicompart- mental and dynamic. Critical variables will be identi- fied, discussed, and averaged in an attempt to make the factors quantitative. Finally, guidelines will be pro- posed for formulating diets. The derived system, although fundamentally logical, contains many constants. Variability in and interactions among these transfer coefficients are largely untested. Field application of the system must await further re- search with a wide variety of feedstuffs and ruminant classes. Consequently, this publication will attempt to describe the biological system, identify the limitations of our information, and propose a system of calculation that needs to be tested, modified, and improved in the future. During these deliberations, several areas were dis- cussed that are not considered here, even though we know that when data are available they will be factors. Such factors as environment and climate, stress, and a variety of other conditions that influence the endocrine balance and thus the metabolism of protein are exam- ples. Also, no consideration was given to the many feed additives that may influence protein metabolism; these are discussed in other publications by the National Re- search Council.

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2 Ruminant Nitrogen Usage Diet Protein N | | Other N 1 1~ ~ . Rumen Reticulum Omasum Abomasum Small Intestine Large Intestine Feces ~ Protein N ~ Other N /l t_ Amino ~< ~ | NH~ r /: ~ _ ~ ~ ~ . | Proteln N _ l ~ . ~ ~ Microbial N - Amino Acids Protein N Other N + _ NH+ 4 ~ ~ "TISSU E" · _ Tissue N Milk N Hair/Wool N Conceptus N Other N Other N NH4 ~- . ~ , ~ 'N `~ , _ Microbial ~ N Amino Acids I `1 _ 1 ~- ~ ~ ' FIGURE 1 Schematic of nitrogen flow in the ruminant. URINE

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Introduction 3 DIET ~ ~ ~ ~ ~ ~ ~ , it's ~:~ ~.~+ ~ 1~ ~ ~ ~ ~U P~ ~ ~:~DiP~ ~ ~ ~ ~ ~ :' ~ 'I ' ' 'I ' :: ~' aid, ~ ~ ~ I; *i- :~ ~ ~':i~ ~R ~ ~ ~ ~ ~ ~ I.. ' ~ ~ ~ : ~ ~ ~ ~ ~ ~ ~ :. ~ ~ ~ ~ ~ ~ ~ ~ n~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - :: ''~''~'~'~' ' ~ ~ T , :, ~ ~ 'I rim r1_n~n . . ! a ~. ~ ~! :: . . A_ r;~s s: sat Hi t~ ~. i@ ~ ~ Hi 1 i_ . _ ~ .,,....,., it:. ~.~..~...~. _ ~ ~.~,~ RUMEN SMALL INTESTINE LARGE INTESTINE ~ VPA'~YP~: . ~ at. ~ ~ ~ .. ~ ~ .~. . ~ ~ .. ~ ~ I. .~ ~ ~ ~ ~ ~ ~ ~ ~ ~ c c, . s. ~. >Gil.; = . 'at, ,,"~.,C ~." Y'.'2~'."' i ;, ~ . ~, .. ~C. I. ~: . . .... .~ .... ~,..,~,,N, FECES FPN UPN FIGURE 2 Schematic diagram of nitrogen flow in the ruminant using symbols developed in this publication.

Representative terms from entire chapter:

nonprotein nitrogen