Year: 1936
Type: article
Abstract: IN studying the digestibility of food protein the normal procedure is to analyse the food for its content of N and to feed a constant amount to experimental animals.After a preliminary period of such length that the faeces can be presumed to represent the experimental ration, the faeces are collected and analysed for a period of 7-10 days.In certain experiments markers have been used to distinguish the faeces of this period from that of the preceding and following periods.The percentage of the ingested nitrogen not appearing in the faeces is called the "coefficient of digestibility of protein".This definition assumes that all the faecal N is derived from the ingested N. Previous work [Schneider, 1934] has shown, however, that the faecal N can be divided into three fractions, (a) a constant fraction found when the animal is fasting, (b) a fraction dependent on the amount of both total dry matter and of indigestible dry matter in the diet and (c) a fraction dependent on the nitrogen content of the diet.METABOLIC FAECAL NITROGEN.Considerable work has been carried out on the metabolic faecal N of the one- stomached animal and its relation to the food intake.Mitchell [1924] concluded that the metabolic faecal N of young growing rats was directly proportional to the food intake.Whilst he recognized the presence of a constant amount of endogenous N he considered it quantitatively of no importance and recom- mended therefore that the metabolic faecal N on a normal diet should be calculated as faecal N/100 g. food intake.-Fixsen and Jackson [1932], working with adult male rats and conse- quently with a much lower food intake, found that the endogenous faecal N was roughly constant for any particular rat and was by no means directly proportional to the food intake.They considered that the food intake should not be taken into account in estimating the metabolic faecal N, in the calculation of the biological value of proteins for maintenance.Schneider [1934] made a statistical analysis of the results obtained in Mitchell's laboratory over a number of years.He confirmed Boas-Fixsen and Jackson's finding that, in an animal eating its maintenance requirements or less, the constant fraction of the metabolic faecal N represented a comparatively large fraction of the total faecal N. Calculation of the metabolic faecal N on the assumption that it is directly proportional to the food intake would thus involve an error as great as if the food intake were not taken into account at all.Where, however, the food intake is above the maintenance requirements of the animal ( 1682 ) Boas
Source: Biochemical Journal
DOI: 10.1042/bj0301682
Institution: Hannah Research Foundation
Language: English
Subfield: Agronomy and Crop Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: bronze
OpenAlex ID: W192558283