Utilization of N15-labelled urea in the laying hen. 6. Incorporation in the liver and kidneys

In an experiment 3 colostomized laying hybrids received a normal ration containing 1% 15N labelled urea with 96.06% atom-% 15N excess (15N') over six days. Subsequently the same ration with unlabelled urea was given over 2 days, after which the animals were butchered. In the kidneys the 15N' amounted to 1.1 atom-% and 1.8 atom-% in the liver. The TCA soluble N fraction and the ammonia were more highly labelled than the total N. Lysine, histidine and arginine were lowly labelled in the kidneys. This also applies to the liver with the exception of histidine. In the branch-chained and aromatic amino acids of the liver the 15N' was between 0.2 and 0.3 atom-%. The highest labelling of non-essential amino acids was found in glutamic acid with 0.9 atom-% 15N' and aspartic acid with 1.1 atom-% 15N'. The evaluation of the amino acid in the liver showed that the 6 non-essential amino acids account for two thirds of the total amino acid 15N' whereas the 9 essential ones account for one third of the amino acid 15N' only.     

Utilization of 15N-labeled urea in laying hens. 7. 15N-incorporation into the amino acids of different muscle types

3 colostomized laying hybrids received 1% 15N labelled urea with 96.06 atom-% 15N excess (15N') with a commercial ration over a period of 6 days. After the application of the same ration with unlabelled urea on the following 2 days the animals were butchered. In the muscles of the breast, the leg and the heart, the labelling of total nitrogen and the incorporation of urea 15N' into 15 amino acids of the 3 different kinds of muscles were ascertained. On average, significant differences could be ascertained between the atom-% 15N of the muscles of the skeleton and those of the heart. The 15N' of the breast and leg muscles was 0.25 and 0.34 atom-% resp.; that of the cardial proteins 0.71 atom-% 15N'. The incorporation of urea 15N into the basic amino acids is low and varies both between the kinds of muscles and between the amino acids. On average the highest level of labelling was found among the essential amino acids valine, isoleucine and leucine; the average atom-% 15N' for the muscles of the breast is 0.13, of the leg 0.17, and of the heart 0.27; the 15N' quota of branched chain amino acids in the total 15N' of the respective muscle is accordingly 6.0%, 5.0% and 4.5%. The non-essential amino acids, particularly glutamic acid, are more highly labelled in the muscles than the essential ones. A 15N' for glutamic acid of 0.24 atom-% in the breast muscles, of 0.27 atom-% in those of the legs and of 0.64 atom-% in the heart muscle could be detected. The average quota of the 15N' of these acid amino acids in the 15N' for breast, leg and heart muscles is 7.4, 6.2 and 6.7 resp. The quota of the 15N' in the 6 non-essential amino acids in the total 15N' in all 3 kinds of muscles is approximately two thirds and in the 9 essential ones one third of the total 15N'. Although the results show that there is a certain incorporation of 15N' from urea into the amino acids of the muscle proteins, their contribution to meeting the demands is to be considered irrelevant.     

Utilization of 15N-labeled urea in laying hens. 9. Bones, feathers and 15N-incorporation in the rest of the body

For studying the incorporation of the 15N labelled urea into individual organs and tissues 3 colostomized laying hens were butchered after they had received 1% urea (96.06 atom-% 15N excess) with a high quality ration over a period of six days and after receiving conventional urea for another two days. Nitrogen and atom-% 15N excess (15N') were determined in the bones, the feathers and the remaining body (skin, lungs and windpipe, head with comb and wattle, lower leg without bones and with skin, pancreas and fatty tissue). In the remaining body the atom-% 15N' was determined in 15 amino acids. The labelling in the remaining body and the bones was approximately the same and averaged 0.37 atom-% 15N'. A significantly lower relative frequency could be detected in the feathers. The lysine of the remaining body contained only 0.04 atom-% 15N', tyrosine 0.06, histidine and arginine 0.07. The phenylalanine and proline molecules were labelled with 0.11 atom-% 15N'. Most 15N' was incorporated in serine and glutamic acid with over 0.30 atom-%. In the six non-essential amino acids out of the 15 amino acids studied, 48.6 of the non isotopic nitrogen of the total N of the remaining body and 70.7% of the isotopic nitrogen of total 15N' could be detected. Consequently the urea-N is mainly used for the synthesis of the non-essential amino acids, with its utilization being very low.     

Dynamics of amino acid and protein metabolism in laying hens after the administration of 15N-labeled wheat protein. 10. 15N-labeling of crude protein and amino acids of the oviducts

Over a period of 4 days 12 colostomized laying hens daily received 36 g coarse wheat meal containing 14.37 atom-% 15N excess (15N') together with a conventional ration. After the homogenisation of each oviduct N and 15N' were determined. After the precipitation with TCA the 15N' of the amino acids was analysed in both the precipitate and the supernatant. In addition, the free amino acids and the peptides were determined in the TCA soluble fraction. The atom-% 15N' in the total N and in the non-basic amino acid N showed a parallel decrease; it diminished from 1.75 atom-% 15N' to 0.64. Of the three basic amino acids, lysine shows the lowest labelling at all four measuring points. The quotas of non-basic amino acid 14N and 15N' in the total 14N and 15N' of the oviduct are the same and amount to 53%. In contrast to this, the quota of the 14N of the basic amino acids in the total 14N of the oviduct only amounts to 21.6% and that of 15N' only to 15.4%. The average atom-% 15N' of the free amino acids 12 h after the last 15N application is 1.54 and is considerably above that of the peptides with 1.15 atom-% 15N'. 36 h after the last 15N application the ascertained value of 1.25 is identical in both fractions. The labelling of the free amino acids decreases more quickly than that of the peptides the more time has passed after the last 15N application.     

Evaluation of 15N marked urea in the laying hen. 4. Incorporation of 15N in blood, its fractions and follicles in various developmental stages

In order to study the utilization of urea in poultry, 3 colostomized laying hybrids were orally supplied with a traditional ration supplemented with 1% 15N'-labelled urea with a 15N excess (15N') of 96.06 atom-% over a period of 6 days. After another 2 days on which the hens received the same ration with unlabelled urea, they were butchered. The atom-% 15N' of the blood on an average of the 3 hens was 0.64, of the plasma 1.40 and of the corpuscles 0.47. The TCA-soluble fraction of the blood had an average 15N' of 1.14 atom-%; the 15N amount is 9.7% of the total amount of 15N in the blood. The amount of 15N' in the urea in the blood was 6.8 atom-%. This shows that the absorbed urea is decomposed very slowly. The quota of 15N' in the basic amino acids from the total 15N' of the blood plasma is only 0.3% and that of the corpuscles 2.2%. The average 15N' of the mature follicles is 2.39 atom-% whereas the smallest and the remaining ovary contain 1.12 atom-%. The labelling level of lysine in mature egg cells was, in contrast to this, only 0.08 atom-% 15N' and in infantile follicles 0.04 atom-% 15N'. 1% of the 15N' quota is in the follicles and the remaining ovary. Of the basic amino acids, histidine is most strongly labelled. The as a whole lower incorporation of the 15N from urea into the basic amino acids shows that the nitrogen of this compound can be used for the synthesis of the essential amino acids to a low degree only.     

Dynamics of amino acid and protein metabolism of laying hens after the administration of 15N-labeled wheat protein. 8. 15N-labeling of nitrogen and 15N incorporation into the amino acids of the liver

Over 4 days 12 colostomized laying hens received, together with the ration, 36 g wheat with 14.37 atom-% 15N excess (15N'), The basic amino acids were nearly equally labelled. Three animals each were butchered after 12 h, 36 h, 60 h, and 108 h after the last 15N' application. Emission spectrometric determination of 15N' in the liver and in the amino acids was carried out. In addition, atom-% 15N' was determined in the free amino acids and the peptides. The labelling in the liver 12 h after the last 15N' application amounted to 1.75 atom-% 15N' and decreased after 108 h to 0.81 atom-% 15N'. The average TCA precipitable 15N' quota in the total 15N' amounted to 81.4% and was nearly identical at all measuring times. The arginine 15N' amount in the liver was twice as high as that of lysine 15N'. In dependence on the period of time after the last 15N' application the decrease in the labelling of the free arginine is considerable in comparison to free lysine. At the first measuring time (12 h) it was 1.69 atom-% 15N' and at the last one (108 h) 0.57 atom-% 15N'. Based on the results of 15N' labelling of the peptides in the liver further, more detailed series of experiments for studies of the peptide metabolism in the liver should be carried out.     

Dynamics of amino acid and protein metabolism in laying hens after the administration of 15N-labeled wheat protein. 2. 15N excretion with nitrogen and basic amino acids of the feces

Over 4 days 12 colostomized laying hens received together with a commercial ration labelled wheat with a 15N excess (15N') of 14.37 atom-%. The labelling of the basic amino acids amounted to 13.58 atom-% for lysine, to 14.38 atom-% for histidine and to 13.63 atom-% 15N' for arginine. 3 animals each were butchered 12 h, 36 h, 60 h and 108 h resp. after the last application of 15N. The heavy nitrogen in the total N and in the N fraction of non-protein origin as well as in the basic amino acids in faeces was daily determined for the individual hens in the total experimental period. On average the crude protein of faeces contained 5.45 % lysine, 2.32% histidine histidine and 3.68% arginine: the protein of faeces correspondingly contained 5.43% lysine, 2.32% histidine and 4.07% arginine. The quota of TCA soluble N in the total N of faeces amounts to one third on the 3rd und 4th days of the experiment and that of 15N' to 28%. The average atom-% 15N' of the protein fraction is 3.48 atom-% 15N' and that of the non-protein N fraction of faeces 2.93 atom-% 15N'. The apparent digestibility and that of the non-protein N fraction of faeces 2.93 atom-% 15N'. The apparent digestibility of the 14N of the ration on average amounts to 82.8% and that of the wheat 15N' to 87.5%. The average quota of the basic amino acids in the protein compounds of faeces amounts to 70.9% for lysine 15N', 73.7% for histidine 15N' and 70.3% for arginine 15N'. The digestibility of the 15N labelled amino acids amounts to 80.4% for lysine, 90.8% for histidine and 90.2% for arginine.     

Dynamics of amino acid and protein metabolism of laying hens after administration of 15N-labeled wheat protein. 5. Incorporation of 15N into the blood fraction and its amino acids

12 colostomized laying hens which received 15N labelled wheat over 4 days were butchered 12 h, 36 h, 60 h and 108 h (3 animals each) after the last 15N application. The intake of 15N excess (15N') from the wheat amounted to 540 mg 15N' during the application period. The 15N' in the blood plasma decreased after the last 15N' application from 0.76 atom-% to 0.55 atom-% after 108 h, the labelling of the corpuscular components at the same measuring points increased from 0.28 to 0.50 atom-% 15N'. 96.6% of the plasma 15N' and 93.8% of that in the corpuscles is precipitable in trichloric acetic acid. The atom-% 15N' of histidine in the total blood remained unchanged in dependence on the butchering time. The 15N amount in lysine and arginine and that in the non-basic amino acids decreased inconsiderably in the period between 12 h and 108 h after the last 15N' wheat feeding.     

First results on the incorporation and excretion of 15N from orally administered urea in lactating pony mares

Two lactating pony mares were given oral offers of 20 g 15N urea [95 atom-% 15N-excess (15N')] on 6 subsequent days. About 80% of the consumed 15N' were excreted via urine and faeces, but only about 2% via milk. The 15N' secreted via milk-lysine only amounted to 0.04% of the 15N' intake. The recovery was about 90% in each case. Tissues with active metabolism had an unexpectedly high labelling (greater than 0.3 atom-% 15N'). The low extent of the conversion of oral urea N into milk-lysine speaks against an essential participation of the enteral synthesis in meeting the amino acid requirement of lactating mares. It was already concluded from this results that the determination of the amino acid requirement will be necessary for this group of performance.     

Utilization of 15N-labelled urea by laying hens. 1. Survey of the literature, 15N-excretion in feces and urine

Three colostomated leghorn hybrids with an average laying performance of 75% received a ration with 17.7% crude protein and an energy content of 519 energetic feed units for hens per kg mixed feed over a period of 8 days. In the first six days of the experiment the 1%-supplement of urea to the ration was labelled. Its atom-% 15N excess (15N') amounted to 96.06%. During the last two days the urea supplement was not labelled. The total N, trichloracetic acid (TCA)-soluble N and the ammonia N were determined in the feces samples collected daily. In the urine samples collected daily the total N, urea N and ammonia N per hen were determined as well. In all samples the atom-% 15N excess (15N') was measured. The percentage of 14N in feces of the 14N dose was, on an average of the three hens, 21.3% and the analogous quota of 15N' 4.6%. The quota of ammonia 14N of the total 14N in feces had an average of 2.5%, the corresponding 15N' quota was 10.1%. The atom-% 15N' of the urea N in urine was considerably above that of the total urine N and had a maximum of more than 50%. The quota of urine 14N of the 14N taken in had an average of 44.4%, and the corresponding 15N' quota was 56.9%. On an average of the three hens, 61.6% of the 15N' were excreted in feces and urine during the 8-day test period.     

Dynamics of amino acid and protein metabolism of laying hens after administration of 15N-labeled wheat protein. 7. Incorporation into the amino acids and peptides of the gastrointestinal tract and the pancreas

In a 15N labelling experiment 12 colostomized laying hens received 15N labelled wheat with 14.37 atom-% 15N excess (15N') over 4 days. 3 hens each were butchered after 12 h, 36 h, 60 h and 108 h after the last 15N' application. The gastro-intestinal tract was divided into 3 parts (oesophagus with crop and gizzard as well as glandular stomach, small intestine, large intestine). These parts and the pancreas were hydrolysed with 6 N HCl and the individual basic as well as the sum of acid and neutral amino acids were determined in the hydrolysed fractions. In addition, the amino acids and peptides were determined in the TCA soluble N fraction. The atom-% 15N' was determined in the individual amino acid and peptide fractions. The labelling of the basic amino acids in the individual tract segments was lower than in the acid and neutral amino acids. In comparison to the peptides, a higher atom-% 15N' could be determined in the free amino acids.     

Metabolism of colostomized laying hens with 15N-labeled wheat. 3. Incorporation of 15N into and its distribution over follicles of various stages of development, the restovar and the oviduct

Of colostomised hens fed with labelled wheat protein the atom-% 15N-excess (15N') was ascertained in the bigger follicles, the restovar and the oviduct from the total N, the lysine-N, histidine-N and arginine-N. The labelling of the basic amino acids decreases the smaller the follicles are. In contrast to the yolk, in which a constant relation between the three amino acids was found, the relations were inconsistent and typical of the individual hens. In the atom-% 15N' in the three amino acids in the restovar and the oviduct there were greater differences between the hens. In the lysine, histidine and arginine we found, on an average, 21.2% of the total labelled N of the follicles.     

15N-labelled lysine in colostomized laying hens. 4. Incorporation of 15N-lysine into various amino acids of egg yolk and white

Each of three colostomized laying hens received per os 0.2% L-Lysine with 48 atom-% 15N-excess (15N') labelled in alpha-position in addition to a pelleted laying hen ration of 120 g over a period of 4 days. On the following 4 days they received equal amounts of unlabelled lysine. The eggs laid during the 8 days of the experiment were separated into the white of egg, the yolk and the eggshell, and the to and heavy nitrogen in the individual fractions were determined. Above that, 17 amino acids and their atom-%15N' were determined in the 19 samples of the white and yolk of egg. Of the total 15N' from the lysine fed in the 4 days, 10.1% were found in the yolk, 10.5% in the white of egg and 1.1% in the eggshells of the eggs laid during the 8 days of the experiment. 85% of the total amino acid-15N' of the yolk and 86% of the white of egg detected to be lysine-15N'. The 15N'-amount of the other 16 amino acids was mainly concentrated in the two acid and basic amino acids. Approximately 50% of the non-lysine 15N' in the egg are contained in aspartic acid, glutamic acid, histidine and arginine. A very low incorporation of the labelled lysine only could be detected in the aromatic and sulphur-containing amino acids from both the yolk and the white of egg. 43% of the 15N' was detected in the 10 essential and semi-essential (except lysine) and 57% in the 6 non-essential amino acids of the yolk and 52% and 48% resp. of the white of egg. One can summarize that the incorporation of 15N' into the egg shows the same development as that of the labelled amino acids of the wheat protein and that 15% of the lysine-15N' could be detected in the 16 other amino acids.     

15N-labeled lysine in colostomized laying hens. 5. 15N incorporation into blood fractions and the gastrointestinal tract

In the metabolism experiment three colostomized laying hens received, together with a commercial ration of 120 g, 0,2% 15N-labelled L-lysine with an atom-% 15N-excess (15N') of 48%; subsequently the same ration was fed over a period of 4 days with 0.2% unlabelled L-lysine. After the end of the experiment the hens were slaughtered. The atom-% 15N' was determined in total, in the lysine, histidine and arginine N in the corpuscles, the plasma, the NPN-fraction of the blood in the stomachs, the small intestine, the caecum and the rectum. 15N' in the corpuscles was 0.11 atom-%, in the blood plasma 0.17 atom-%, in the NPN-fraction of the blood 0.09 atom-%, in the tissue of the gastro-intestinal tract 0.11 atom-% and in its contents 0,12 atom-%. On average the blood contained per hen 77.9% lysine-15N', 16.4% arginine-15N' and 5.7% histidine-15N' of the basic amino acid-15N'. For the gastro-intestinal tract 78.7% lysine-15N', 19.0% arginine-15N' and 2.3% histidine-15N' of the 15N' of the basic amino acids were ascertained. In comparison to histidine the alpha-amino-N of lysine is incorporated to a considerably higher degree into arginine. For lysine and arginine the atom-% 15N' in the contents of the gastro-intestinal tract for days after the end of the supplementation of labelled lysine is between 8 and 10 times higher than in the feces of the last day of the experiment. This indicates a considerable secretion of the two amino acids in the gastro-intestinal tract and their re-absorption to a large extent.     

Dynamics of amino acid and protein metabolism of laying hens after the administration of 15N-labeled wheat protein. 3. Incorporation of 15N into egg shell, egg white and egg yolk

12 colostomized laying hybrids received a ration meeting their requirement of 15N labelled wheat with a 15N excess (15N') of 14.37 atom-% over 4 days. The 15N' of the total ration amounted to 4.47 atom-%. Each hen consumed 135 mg 15N' per day. On another 4 days the same rations with non labelled wheat were fed. The 12 hens laid 56 eggs during the 8 days of the experiment. They were divided into egg shell, white and yolk of egg. In addition, the protein of the white and yolk of egg was precipitated with trichloric acetic acid (TCA) and the nitrogen in these fractions was determined. On average of the 56 eggs, the N quota in the egg shell was 5.3%, in the white of egg 49.1% and in the yolk 45.6%. The atom-% 15N' in the shells of the eggs laid on the first day of the experiment was on average 0.21, whereas only 0.03 and 0.02 atom-% 15N' resp. could be detected in the white and yolks of the eggs. On the first day after the last 15N application the atom-% 15N' in the egg shell and the white of egg was highest and amounted to 2.33 and 2.43 atom-% resp. The highest value of 1.83 atom-% 15N' in the yolk was ascertained 3 days after the last 15N intake. The mean quota of TCA-precipitable N in the white of egg is 97.6% and in the yolk 94.4% of the respective total N. The atom-% 15N' in the non-protein N-compounds was higher than in the protein fractions.     

The utilization of crude proteins from 15N-labeled straw by broiler hen breeds

In an experiment with 10 colostomized broiler breeding hens the digestibility of wheat straw meal labelled with 15N and the incorporation of heavy nitrogen into individual body fractions were studied. The straw meal contained a 15N excess (15N') of 14.88 atom-%. Before the experiment part of the straw meal was treated with gamma-rays (2.0 MGy). 5 animals each received in addition to the basic ration 30 g untreated (group I) and irradiated 15N labelled straw meal (group II). The apparent 15N' digestibility amounted for untreated straw meal to 49% and for irradiated straw meal to 46% (p less than 0.05). The labelling of uric acid amounted to 0.25 atom-% 15N', urine with 0.30 atom-% 15N' was more highly labelled (p less than 0.05). On an average of both groups the same labelling of 0.18 atom-% could be detected in the follicles and the liver, whereas 0.17 were ascertained in the blood plasma and 0.16 atom-% 15N' in the oviduct. 18% of the digested 15N' were incorporated in the muscles. There were only insignificant differences between the two groups with regard to the incorporation of 15N'. In conclusion one can say that the apparent digestibility of straw protein is 47.5% and that the utilization of the absorbed N is about the same as that of wheat protein.     

Urea utilization in growing lambs. 6. N balance with 15N urea

Lambs of an age of 2 or 4 months and of an average live weight of 14.7 and 27.4 kg resp. received rations consisting of 44% cereals, 46% dried sugar beet pulp, 6% wheat starch, 2% urea and 2% mineral-vitamin mixture. The crude protein content was 17.1 and 15.9% resp. in the dry matter, that of native crude protein 10.6 and 9.4% resp. During a 6-day N balance period 8 and 16 g 15N urea resp. with a 15N excess (15N') of 9.26 and 9.40 atom-% were fed orally instead of commercial feeding urea. There were no significant differences between the two age groups with regard to the digestibility of the organic matter and the crude nutrients. The average N balance of 372 +/- 85 mg/kg LW 0.75/day were in the intermediate range of N retention capacity and accounted for 26 +/- 5% of the consumed N. N retention in per cent. was slightly lower in younger lambs. Projections of urea utilization in a quasi stationary state resulted in an efficiency of the utilization of 33 +/- 4%. The dismembering of the lambs at the end of the main period showed between 0.02 and 0.22 atom-% 15N' in the total N, TCA precipitable N and amino acid N of the meat. At between 0.24 and 0.38 atom-% 15N' they were highest in the heart and jaw muscles. The quota of 15N' amounts found in the total N of the meat were 10.6 +/- 3% of the 15N-intake and 20.1 +/- 5.1% of the 15N' amount remaining in the body. The bones contained 7.7 +/- 1.7% and the fleece 7.9 +/- 3.1% of the 15N'-intake. Generally seen, the total N and urea utilization was slightly lower in younger lambs than in older ones.     

Utilization of N15-labelled urea in the laying hen. 5. N15-labelling of the content and tissue of separate parts of the gastrointestinal tract

In the series of experiments with labelled urea three colostomized laying hybrids were butchered after a six-day application of 1% urea with 96.06 atom-% 15N excess (15N') in the ration and another 2 days with a supplement of 1% unlabelled urea. Out of the individual samples from crop, gizzard, small intestine, caecum and rectum, the content of the small intestine and the caecum showed the highest labelling with greater than 1 atom-% 15N'. The TCA soluble fraction of the content of the gizzard was more highly and that of the intestines less labelled than the total nitrogen. The tissue of the gizzard is distinctly less labelled than the "omasum system" and the small intestine. The atom-% 15N' of the oesophagus with crop and glandular stomach largely showed agreement in the individual hens with that of intestinal tissue and ranged between 0.71 and 0.89 atom-%. 2% of the 15N' supplemented with the urea could be recovered in the content and the tissue of the gastro-intestinal tract.     

The utilization of 15N-labeled urea by the laying hen. 3. Incorporation of labeled nitrogen into the amino acids of the white and egg yolk

In an experiment with 3 colostomized laying hens the incorporation of heavy nitrogen from urea into the amino acids of the 21 eggs laid during the 8-day experiment was ascertained. In these eggs the content of 15 amino acids was ascertained separately in the whites and yolks of the eggs and their atom-% 15N-excess (15N') was determined. The heavy nitrogen could be detected in all amino acids investigated. The incorporation of 15N' into the essential amino acids of the white and yolk of eggs is very low. Of the applied 15N'-amount of the urea 0.18% could be detected in the 9 essential amino acids of the white of egg and 0.12% in those of the yolk. For the 6 analysed nonessential amino acids the rediscovery quota of 15N' in the white of egg was 0.50% and in the yolk 0.81%. The conclusion from these results is that the NPN-source urea is insignificant for egg protein synthesis.     

Dynamics of amino acid and protein metabolism of laying hens after the administration of 15N-labeled wheat protein. 1.Problems, research program and 15N-labeling of urine

In a 6-day preliminary period with a pelleted ration 12 colostomized laying hybrids received 15N labelled wheat protein over 4 days. The labelling of the wheat was 14.37 atom-% 15N excess (15N'). During the 4-day application of 15N wheat protein each hen consumed 12.08 g nitrogen, 3.52 g lysine, 2.12 g histidine, 4.41 g arginine, of which were 540 mg 15N', 18.1 mg lysine 15N', 21.5 mg histidine 15N' and 47.9 mg arginine 15N'. Heavy nitrogen was determined in urine and its uric acid-N in the daily urine samples of the individual animals. The average daily urine N excretion was 54% of the total nitrogen consumed with the ration. The labelling of the urine N reached a plateau on the fourth day of the experiment with 3.2 atom-% 15N'. On an average of the total experiment the quota of heavy nitrogen of the uric acid in the total 15N' of the urine was 83.4% and that of uric acid nitrogen in the total urine nitrogen 80.8%.