Incorporation of 14C-amino acids into egg proteins by the laying hen

[Protein and amino acid metabolism in laying hens receiving N-15 labeled casein. 7. Incorporation and distribution of labeled nitrogen into egg fractions]

Four colostomated hybrid laying hens were fed, for 6 days, a semisynthetic ration containing 15N labelled casein as sole protein source. Within this period, the hens laid 13 eggs which were fractionated into egg yolk, egg white and egg shell. The N content of these egg fractions was established. A TCE soluble and TCE precipitable fraction (TCE=trichloroacetic acid) were obtained from the fractions of egg yolk and egg white. Additionally, an analysis was made of the set of amino acids contained in the crude protein of the egg yolk, egg white and egg membrane (lysine, histidine and arginine only). The excess 15N atom% (15N') was established in the crude protein, in the nitrogen from the TCE soluble and TCE precipitable fractions and in the N from 17 amino acids of the egg yold and egg white. In the egg membrane fraction the 15N' atom% was determined as percentage of the total amount of N and of the amount of N contained in the basic amino acids. Essential differences between the 3 egg fractions were noticed with regard to the process of initial incorporation of labelled N and the intensity of this process after the onset of 15N application. 15N' was detected in the egg shell as early as 4 hrs after administration of the 15N' dose. Heavy nitrogen was found to be contained in the egg white of eggs that were laid on the 2nd day of experiment. The level of 15N' atom% in the egg white increased essentially during the following days of experiment; the 15N'quantities in the egg white were considerably higher than those in the egg yolk. Similar results were obtained for the process of 15N incorporation into the 17 amino acids. It is assumed that differences between the 3 fractions as observed in the level of labelling and in the pattern of 15N' incorporation are accounted for by the different sites and different times of protein synthesis for the different egg proteins.

[Substitution of protein feed through lysine-supplemented high-protein wheat during the rearing and laying period of hens. 3. Effect of graded lysine doses on the crude nutrient content of carcasses and on the level of amino acids and GOT activity in the blood of young hens]

A large-scale trial was carried out under commercial conditions to investigate to which extent the feeding of rations with varying lysine content to young hens would influence the crude nutrient content of the body fractions and might change the pattern of amino acid composition and the activity of GOT in the blood. Four rations were fed each containing 14.2% crude protein, 626-633 EFh units/kg and 0.59%, 0.61%, 0.54% and 0.46% lysine. The crude protein and crude fat content of the total body and of body fractions were in no case found to be related to the feeding regime. The proportion of crude ash in the "remainder of non-utilizable parts", in "bones", "intestinal and abdominal fat", "ovaries" and "small intestine" decreased with the decreasing lysine content of the rations. The concentrations of free lysine, histidine, arginine, and phenylalanine in the deproteinized blood plasma of the young hens were significantly (a = 0.01) lower in the birds of the lysine deficient group than in the hens of the other groups. Positive regressions were calculated for the lysine content or the content of aspartic acid in the ration and the pattern of free amino acids in blood plasma. Positive and negative linear relationships were found to exist between the concentrations of free lysine, and those of histidine, arginine or threonine, and serine. A close correlation existed between the total amount of essential amino acids in blood plasma and the lysine concentrations of the plasma. Increasing lysine supplementation produced a decline in the N content of the whole blood and blood corpuscles but a rise in the N content of blood plasma. The activity of GOT in the blood of young hens was not found to be useful as an indicator of the quality of dietary proteins.