A study of digestibility and biological value of protein in diets fed to colostomised laying pullets to determine their protein requirement

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Abstract
Hybrid pullets were colostomised just after the commencement of laying. A nitrogen‐free diet was used to determine metabolic faecal nitrogen (MFN) and endogenous urinary nitrogen (EUN). The mean figure obtained for MFN/kg. wt./100 g. dry matter/day was 67.2 mg. and for EUN/kg. body weight 3/4/day was 83.3 mg. High energy diets of about 1350 k cal./lb. containing 13, 15 and 17 per cent protein and medium energy diets of 13 and 17 per cent protein were fed to colostomised pullets to determine their digestibility, biological value and net protein value. In a further experiment a maize‐fishmeal diet of 1370 k cal. ME/lb. and 17 per cent protein, a soyabean‐maize diet of 1330 k cal. ME/lb. and 14 per cent protein and the latter diet supplemented with methionine and/or lysine were also examined. The mean BV and NPV values of the diets considered in Experiment 1 were 60 and 52 respectively. Addition of methionine to the maize‐soyabean diet increased the BV from 43.9 to 61.6, the addition of lysine to 43.0 and the addition of both to 67.1. A factorial method of calculating the daily protein requirement of the pullet based on the data for MFN and EUN and the NPV of each diet is presented. The estimate of 13.3 g. protein per day for the hybrid pullet is compared with other estimates in the literature.