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The nutritive value of certain noxious weed seeds Robertson, Mary Chalmers

Abstract

An attempt has been made to assess the nutritive value of the proteins of a number of weed seeds which are considered as noxious under the Canada Feeding Stuffs Act, but which have been fed successfully to ruminants in the form of heat processed refuse screenings. These weed seeds contain isothiocyanates which may or may not be toxic to animals but which were found to be unpalatable to the rat. For this reason it was found necessary to take two approachs to the problem of determining the nutritive value of these weed seeds; a direct approach involving animal assays with rats and an indirect approach involving assessment of the essential amino acid content of these weed seeds. In carrying out these objectives a study of the properties of the isothiocyantes themselves and of the various methods for evaluation of protein quality were also undertaken. For the direct approach involving animal assays, an attempt was made to develop a procedure which would remove the isothiocyanates from samples of these weed seeds. A procedure involving auto-hydrolysis of the weed seed with water followed by extraction with 70% ethanol was evolved. This treatment reduced the isothiocyanate content of the weed seeds and rendered them palatable to the rat. Using samples prepared in this manner the proteins of a number of the weed seeds were assayed for their net protein utilization according to the method proposed by Miller and Bender (89). Since there was no assurance that attempts to remove the isothiocyanates would be successful, an indirect approach was also taken for the evaluation of the proteins of weed seeds. A number of weed seeds were analysed, for their content of essential amino acids using the microbiological assay methods proposed by Barton - Wright. From this data, a chemical evaluation of the proteins was carried out through computation of "essential amino acid indices" and "chemical scores" according to the method proposed by Mitchell. A comparison and correlation of the animal assays and chemical evaluations indicated that although slightly lower in value the proteins of weed seeds compare favourably with those of soybean and linseed as plant proteins of moderately high biological value. In connection with the evaluation of proteins by the Miller and Bender method a study was made of the body water -body nitrogen relationship in the U.B.C. colony of rats. The body water and body nitrogen content of 58 Wistar and 36 Sprague - Dawley rats were determined and regression equations correlating body nitrogen to body water were calculated. These investigations confirmed the findings of other workers that the nitrogen to water ratio varies with such constancy that the nitrogen content of an animal can be calculated from a knowledge of its water content and age or body weight.

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