Nutrient requirements for maintenance

An animal is in a state of maintenance when its body composition remains constant, when it does not give rise to any product such as milk, and when it does not perform 

The animals exemplified in Table 14.1 are all highly productive, but less productive animals use proportionately more of their energy intake for maintenance. It may be calculated, for example, that, on average, cattle in Africa use about 85 per cent of their energy intake for maintenance. 

As explained earlier (see p. 261), energy expended in the maintenance of an animal leaves the body in the form of heat. The quantity of heat arising in this way is known as the animal s basal metabolism, and its measurement provides a direct estimate of the NE that the animal requires from its food in order to meet the demands of maintenance. The measurement of basal metabolism is complicated by the fact that heat produced by the animal comes not only from this source but also from the digestion and metabolism of food components (the heat increment of feeding) and from the voluntary muscular activity of the animal. Heat production may also be increased further if the animal is kept in a cold environment (see p. 350). 

This replacement in the mixture of carbohydrate by fat is accompanied by a decline in the non-protein respiratory quotient, and when the theoretical value for fat (0.7) is reached it can be assumed that energy is being obtained only from body reserves. In ruminants, an additional indication that the post-absorptive state has been reached is a decline in methane production (and therefore digestive activity) to a very low level. 

There has been considerable discussion as to whether surface area orW (often called metabolic liveweight) is the better base. This will not be repeated here but is contained in the books listed in Further reading. Mathematically, there is nothing to 

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Chapter 14 covers the nutrient requirements for maintenance and growth and explains how growth can be controlled by nutrient supply. 

Derived plant and animal products make better use or upgrade the nutritional quaHty of already existing materials or products. Synthetic and manufactured products arose from knowledge of the functional properties of food ingredients and of human and animal nutrition that involved more precise definition of nutrient requirements for growth, reproduction, lactation, and body maintenance in both humans and domestic Hvestock. Pood products have been developed to meet human needs under abnormal environments, eg, military rations for arctic, tropical, or desert environments, and special products for astronauts ia space flights. 

Hundreds of biochemical reactions take place even in the cells of relatively simple microorganisms. Living systems have evolved a sophisticated hierarchy of controls that permits them to maintain a stable intracellular environment. These controls ensure that substances required for maintenance and growth are produced in amounts that are adequate without being excessive. Biochemical controls have developed in such a way that the cell can make adjustments in response to a changing external environment. Adjustments are needed because the temperature, ionic strength, acid concentration, and concentration of nutrients present in the... 

Figures 6.3 and 6.4 show a conceptual flowchart of the energy in an ecological system. The energy input during time interval t is provided by solar radiation EA(t, ip, A, z), as is the upward transport of nutrients from deep-sea layers. The concentration of nutrients B6A(t,ip, A,z) at depth z is determined by photosynthesis RpA, advection, and destruction of suspended dead organic matter B-j. The role played by hydro-dynamic conditions relates to maintenance of the concentration of nutrients required for photosynthesis which occurs via transport from other layers or aquatories of the sea where the concentration is sufficiently high. Taking into account the designations of Table 6.7 we have...

Because there is no growth during the stationary phase, it is clear that Eq tion (7-70) cannot be used to account for substrate consumption, nor can the i of product formation be related to the growth rate (e.g.. Equation (7-63)]. M. antibiotics, such as penicillin, are produced in the stationary pha.se. In this phi the nutrient required for growth becomes virtually exhausted, and a different nc ent, called the secondary nutrient, is used for cell maintenance and to produce desired product. Usually, the rate law for product formation during the station phase is similar in form to the Monod equation, that is. 

The influence of climate on the nutrition of farm animals is not confined to energy requirements for maintenance but extends to other aspects of energy metabolism and also to nutrients other than energy. Nevertheless, climate has the greatest influence on energy requirements, and in cold climates animals kept at or below the maintenance level are most affected. 

The nutrient requirements of the lactating goat may be derived factoriaUy from estimates of the requirements for maintenance, milk production and liveweight change. 

All bacteria utilize nutrients as sources of the energy required for all of the biosynthetic processes that bacteria use for their maintenance and reproduction. Bacteria... 

Water accounts for over half the body mass (55%) of the average human. Of the remaining 45%, 19% is protein, 19% is lipid, less than 1% is carbohydrate, and 7% is inorganic material. Nutrients must contain the raw materials that go into the construction of the components of the human body. In addition, nutrients must supply the necessary chemical energy and enzyme cofactors (vitamins and trace metal elements) that are required for the maintenance and growth of the human body. The human body requires nutrients such as water, amino acids, fats, carbohydrates, and major minerals in large amounts. Vitamins and trace metal elements are required in smaller amounts. 

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