Energy metabolism studies with sheep

Graham, Norman M (1959) Energy metabolism studies with sheep. PhD thesis, University of Glasgow.

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As the population of the world increases and man's standard of living it becomes increasingly important that the world's supplies of animal feedingstuffs should be used efficiently and that waste should be minimised. It this is to he accomplished the waste value of feedingstuffs must be known accurately. The work described in the present thesis is part of extensive investigations that are now being made to obtain precise information on the energy metabolism of farm animals and on the ability of different feedings tuffs to satisfy their energy requirements for maintenance, for growth and for the production of meat, milk and wool. The object of the present experiments was development of a reliable method that could be used extensively for the determination of the net energy values of animal feedingstuffs. Sheep used as the experimental animals and closed-circuit respiration calorimetry was used to measure their energy exchange. The thesis is divided into three main parte. In the first part a description is given of the experimental methods and of the closed-circuit respiration apparatus. The energy retention of the sheep was calculated m the difference between the energy intake and energy losses (Respiratory Quotient or R.Q, method) and also as the energy stored in body fat and protein (O/H method). The relative merits of these two methods are discussed. The second part of the thesis describes, the five experiments comprising the main part of the work. The more important results are summarised in tables in the text, and the detailed results are available for reference in a series of tables in an appendix. In the first experiment the heat productions of eight sheep were measured and it was shown that the sheep used for this type of work must be carefully trained to accustom them to the experimental routine in order to ensure that their basal metabolism remains reasonably constant, The second experiment showed that when one type of feedingstuff is to be tested immediately after another, the sheep must be fed at least 10 days on the ration before measurements of energy exchange are made. The results of the third experiment made it clear that the net energy value of a given weight of dried grass is not constant but that it decreases as the amount eaten is increased. This is due mainly to the fact that at the higher levels of feeding the digestibility of the dried grass is reduced and the amount of heat produced from the digested portion is increased. It was found that there was a curvilinear relationship between energy retention and energy intake, and an expontial equation was derived to describe that relationship. The effects on the energy exchange of feeding dried grass in different physical forms and of altering the frequency of feeding was studied in the fourth and fifth experiments. It was found that the net energy value of dried grass was not altered by the process of grinding and cubing except at very high planes of nutrition. Frequency of feeding also had no significant effect on the utilisation of the energy of chopped dried grass although the methane production of the sheep was slightly less when they were given one large meal each day than it was when they were given the same amount of grass per day in four email meals. In the third part of the thesis the results and methods are discussed and the net energy values which were obtained by direct determination are shown to differ markedly from those computed from digestibility data by the methods of Kellner and Armsby. The causes of the disagreement are discussed and a method of expressing net energy values to take account of variations in level of feed is described. The work has led to the conclusion that net energy values can be measured to within +/- 2% by the respiratory quotient method using the apparatus and techniques described hut in order to obtain this accuracy, results must be obtained for three widely-separated planes of nutrition (one of which could he the fasting level) with at least four sheep: with only one respiration chamber the determination in this way of the net energy value of one feedingstuff would require a period of 10 weeks.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: K L Blaxter
Keywords: Animal sciences
Date of Award: 1959
Depositing User: Enlighten Team
Unique ID: glathesis:1959-73692
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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