Calorimetry animal

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

By far, the most suitable method to quantify individual ruminant animal CH4 measurement is by using respiration chamber, or calorimetry. The respiration chamber models include whole animal chambers, head boxes, or ventilated hoods and face masks. These methods have been effectively used to collect information pertaining to CH4 emissions in livestock. The predominant use of calorimeters has been in energy balance experiments where CH4 has been estimated as a part of the procedures followed. Although there are various designs available, open-circuit calorimeter has been the one widely used. There are various designs of calorimeters, but the most common one is the open-circuit calorimeter, in which outside air is circulated around the animal s head, mouth, and nose and expired air is collected for further analysis. 

In practice, animal calorimetry is quite complicated because of the inherent difficulty of accurate heat measurements, uncertainties about the amount of food stored, and the necessity of corrections for AHc of the waste products. However, the measurement of energy metabolism has been of considerable importance in nutrition and medicine. Indirect methods of calorime-tery have been developed for use in measuring the basal metabolic rate of humans. For a good discussion see White et al.u... 

The term indirect calorimetry is often used in biology when the sum of metabolic processes in an animal, e.g., a human being, is investigated by measurement of rates of consumption of oxygen and the production of carbon dioxide and... 

Dauncey, MJ. (1991). Whole-body calorimetry cm man and animals. Thermochim. Acta 193, 1-40. 

The energy expenditure of an animal or human may also be determined by the method of direct calorimetry. Direct calorimetry requires the use of an insulated room, chamber, or suit for the human or animal. The enclosure contains a water jacket. The water passes from one end of the jacket to the other, maintaining the room, chamber, or suit at a constant temperature. The temperature of the water leaving the jacket is used to calculate the energy expended by the subject. The principles behind the use of the chamber are identical to those behind the use of the bomb calorimeter. The major difference is that in bomb calorimetry combustion is catalyzed by a small spark. In addition, in the bomb calorimeter oxygen is present at a high pressure to facilitate combustion. With direct calorimetry, combustion is catalyzed by enzymes. This combustion proceeds more slowly than that catalyzed by a spark, and the temperature of the subject does not increase much over the normal resting body temperature with the various activities. 

Since calorimetric data are a measure of rate, it is possible to link heat output with the metabolic activity of human (and animal) cells. Both types of cell have been extensively studied by flow calorimetry one example is the study and optimization of Chinese hamster ovary cells producing recombinant interferon y-... 

The influence of plant sterols on the phase properties of phospholipid bilayers has been studied by differential scanning calorimetry and X-ray diffraction [206]. It is interesting that the phase transition of dipalmitoylglycerophosphocholine was eliminated by plant sterols at a concentration of about 33 mole%, as found for cholesterol in animal cell membranes. However, less effective modulation of lipid bilayer permeability by plant sterols as compared with cholesterol has been reported. The molecular evolution of biomembranes has received some consideration [207-209]. In his speculation on the evolution of sterols, Bloch [207] has suggested that in the prebiotic atmosphere chemical evolution of the sterol pathway if it did indeed occur, must have stopped at the stage of squalene because of lack of molecular oxygen, an obligatory electron acceptor in the biosynthetic pathway of sterols . Thus, cholesterol is absent from anaerobic bacteria (procaryotes). 

Interactive Figure To see an animation of calorimetry, visit qlencoe.com. 

J. A. McLean and G. Tobin, Animal and Human Calorimetry, Cambridge University Press, Cambridge, 1988. 

Another goal of the USDA study was to determine whether CLA enhanced energy expenditure, lipolysis, or fat oxidation in humans, similar to the effects observed in animals. Accordingly, measurements of metabolic rate and respiratory quotient were made by indirect calorimetry, and stable isotope tracers of palmitate and glycerol were used to measure the rate of appearance of free fatty acids and glycerol as well as whole body lipolysis and apparent reesterification. CLA supplementation had no effect on metabolic rate or whole-body fat oxidation rate during rest or exercise. Similarly, CLA did not change lipolytic rate, fatty acid release from adipose tissue, or apparent FFA reesterification rates under conditions of rest or exercise (33). 

Animal calorimetry methods of measuring heat production and energy retention... 

ANIMAL CALORIMETRY METHODS FOR MEASURING HEAT PRODUCTION AND ENERGY RETENTION... 

Calorimetry means the measurement of heat. The partition of food energy presented in Fig. 11.2 shows that if the ME intake of an animal is known, then the measurement of its total heat production will allow its energy retention to be calculated by difference (likewise, the measurement of energy retention will allow heat production to be calculated). In practice, measurement of either heat production or energy retention is used to establish the NE value of a food. 

The methods used to measure heat production and energy retention in animals can be quite complicated, both in principle and in practice. In the past, the complexity and cost of the apparatus required for animal calorimetry limited its use to a small number of nutritional research establishments. Improved fimding of research has gradually removed this restriction, but even so, animal calorimetry remains a specialised topic and few nutritionists become involved in it. Nevertheless, the study of animal calorimetry on paper (as in this book) is valuable to all students of nutrition, because it reinforces their knowledge of the principles of energy metabolism. In the pages that follow, the principles of the methods used in animal calorimetry are explained within the main body of the text, and the apparatus employed is described in Boxes 11.3,11.4 and 11.5. 

The heat production of animals can be measured physically using a procedure known as direct calorimetry. Alternatively, heat production can be estimated from the respiratory exchange of the animal. For this, a respiration chamber is normally used and the approach is one of indirect calorimetry. Respiration chambers can also be used to estimate energy retention rather than heat production, by a procedure known as the carbon and nitrogen balance technique. 

Because animal calorimeters are expensive to build and earlier types required much labour to operate them, animal calorimetry today is mainly carried out by the indirect method described below. 

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