[Influence of the physical properties of straw pellets on their digestibility and passage rate of Cr2O3 in sheep]. / Einfluss der physikalischen Eigenschaften von Strohpellets auf deren Verdaulichkeit und die Passagerate von Cr2O3 bei Schafen.

By means of pelleting them one to four times (press G 600) and adding 20% sugar beet chips and 3% ammonia hydrogen carbonate at varying loose density (357-561 kg/m3) 4 straw pellet charges were produced. Significant differences could be ascertained for these pellets with regard to the fineness coefficient (I-IV 1.67; 1.30; 1.19; 0.83), hardness of pellets (5.4; 8.8; 9.4; 18.6 N/m2/10(5) and partly the loose volume. After testing four wethers per group, an energy concentration in the same sequence was ascertained as follows: 409, 388, 377 and 382 EFUcattle/kg dry matter. Apart from a higher crude fibre digestibility of groups I and II compared to III there were no significant differences in the digestibility. The measuring of feed passage time with the help of Cr2O3 did not result in directed differences. On an average of all groups, 80% of the Cr2O3 excretion was achieved after 70.5 +/- 0.7 h. The mean retention time of Cr2O3 in the digestive tract in all four groups was in average 53.3 +/- 1.2 hours. The different fineness degrees and values of the hardness of straw pellets remained without significant effects on the feed value of the straw pellets in the experiments with sheep.

[Nitrogen exchange in the large intestine of ruminants. 4. Exchange and isotope balance of intracecally administered 14C- and 15N-urea in sheep with simultaneous intracecal dose of a partly hydrolyzed straw meal]. / Untersuchungen zum Stickstoffumsatz im Dickdarm von Wiederkäuern. 4. Mitteilung. Umsatz und Isotopenbilanz von intrazäkal verabreichtem 14C- und 15N-Harnstoff bei Schafen bei gleichzeitiger intrazäkaler Gabe von teilhydrolysiertem Strohmehl.

Two experiments were performed with wethers (Body weight 34 to 44 kg) receiving a ration rich in crude fibre at maintenance level. The animals were fitted with ileocaecal cannulas into which 14C-, 15N-labelled urea together with digesta was introduced hourly for a 24 hours period (V1; 2 animals). In experiment two (V2; 3 animals) in addition HCl-partly hydrolysed straw meal was introduced. After ureolytic degradation the intracaecal applied urea entered mainly the intermediary metabolism. The resulting ammonia was resynthesized to urea without any time lag. The rate constant for the increase in 15N labelling of urea was 3.2 d-1 in both experiments. Urea leaves the plasma with half lives of 10.6 (V1) and 5.2 (V2) hours. More than 60% of the applied urea were excreted with urine. Formed 14CO2 appeared at proportions of 66% (V2) and 71% (V1) in the respiration gases. Both, the decline of the 14C-activity in blood plasma and the specific 14C-activity of CO2 in the respiration gases after the end of the labelling period do not follow a kinetic of first order. The 15N-labelling of the NH3-N in ileal digesta was very high and reached plateau values similar with those of plasma urea (2.54 vs. 2.56 atom-% 15N-excess). A direct entry of plasma urea into the small intestine was concluded.

[Nitrogen metabolism in the large intestine of ruminants. 3. Microbial utilization of intracecally administered 14C- and 15N-marked urea in the large intestine of sheep in simultaneous intracecal administration of partially hydrolyzed straw meal]. / Untersuchungen zum Stickstoffumsatz im Dickdarm des Wiederkäuers. 3. Mitteilung. Mikrobielle Verwertung von intrazäkal verabreichtem 14C- und 15N-markiertem Harnstoff im Dickdarm von Schafen bei gleichzeitiger intrazäkaler Gabe von teilhydrolysiertem Strohmehl.

Two experiments were performed on sheep, receiving on maintenance level a pelleted straw ration high in crude fibre (straw, 70.5%; dried sugar beet pulp, 12%; cereals, 10%; urea, 2%; ammonium hydrogen carbonate, 3%; minerals 2,5%). The animals were fitted with ileo-caecal re-entrant cannulas. The effects of the introduction of HC1-partly hydrolysed straw meal into the digesta of the large intestine on the digestion processes in that segment were studied. Under these conditions the metabolism of 14C and 15N labelled urea, which was given into the caecum, was estimated. In experiment 1 (E 1; 2 animals) unlabelled, precollected digesta were hourly reintroduced together with 14C and 15N labelled urea via the caecal cannula. In experiment 2 (E 2; 3 animals) the digesta were supplemented with partly hydrolysed straw meal (10% of the mean daily DM-intake with the ration). The supplement of partly hydrolysed straw meal caused an increase of the 15N excretion with faeces from 13.4% (E 1) to 19.8% (E 2) of the dose. The 15N was mainly incorporated in the bacterial fraction (98% E 1; 96% E 2). As a reason for the increased 15N incorporation into the bacterial fraction of 106.4 mg15N' in E 2 vs. 67.3 mg15N' in the experiment without straw meal supplement the higher supply of energy as fermentable carbohydrates was assumed.

[Nitrogen metabolism in the large intestine of ruminants. 1. Metabolism of i.v. infused 15N-urea without additional carbohydrate supply to the large intestine]. / Untersuchungen zum Stickstoffumsatz im Dickdarm des Wiederkäuers. 1. Mitteilung. Umsatz von i. v. infundiertem 15N-Harnstoff ohne zusätzliche Kohlenhydratversorgung des Dickdarms.

The experiments were carried out on 3 bulls (body weight: 172, 229 and 193 kg), equipped with ileo-caecal cannulas and with catheters in the jugular veins on both sides. The offered pelleted ration consisted of straw 73%, molasses 12%, cereals 10%, ammonium hydrogen carbonate 3% and urea 2%. Feed intake amounted to about 3 kg per animal and day. During a preliminary period of 5 days 50% of ileal digesta were collected for 12 hours daily, deep-freezed and stored. In the main experiment 15N-urea was infused intravenously for 24 hours. During this period and during the following 6 hours ileal digesta were collected and replaced by precollected, unlabelled digesta. The urea metabolism was estimated by the 15N-labelling of blood urea, by the 15N-excretion via faeces and urea, by the appearance of 15N in ileal digesta and by the 15N-labelling of faecal NAN, NH3 and bacterial fraction. The time course of the 15N-labelling of plasma urea during infusion can be described by an exponential function. The urea flux rate was estimated from the calculated plateau value. The flux rate for the 3 animals was 28.8, 30.7 and 34.8 mumol per minute per kg0.75, respectively. During the infusion of 15N-urea 1.0-2.4% of the infused amount of 15N' appeared in ileal digesta, half of it in the TCA precipitable fraction. At the same time the 15N-labelling of faecal NH3 increased sharply, however, the 15N-labelling of the faecal bacterial fraction was smaller by one order of magnitude. Deficiency of fermentable substrates and problems of inhomogenity of the NH3 pool are supposed as reasons for this result. 30 to 50% of the urea flux entered the digestive tract, the direct entry of urea into the large intestine seems to be only very low.

Investigations of the influence of the content of plant crude protein in the ration on the utilisation of urea in dairy cattle. 5. 15N-fractions in the blood of lactating cows given 15N-urea intraruminantly.

The incorporation of urea-15N (given as an intraruminal drench or infusion) into plasma urea and protein of dairy cows fed isoenergetic rations with different levels of plant protein (9, 11, 12, 14, 15 and 17% in DM) was investigated. A nonlinear and asymptotic dependence between the plasma concentration of urea and protein level in the ration was stated. The availability of dietary urea-15N for plasma urea for 48 hours after administration was lowest in cows fed with low protein rations (9 and 11% of plant protein). On the contrary the highest incorporation of urea-15N into plasma protein of these animals was observed. The possible explanation of these results is presented.

[Isobutylidene urea as NPN source for ruminants. 2. Digestion of 15N-labeled isobutylidene urea in lactating dairy cows]. / Isobutylidendiharnstoff als NPN-Quelle für Wiederkäuer. 2. Mitteilung. Umsatz von 15N-markiertem Isobutylidendiharnstoff bei laktierenden Milchkühen.

Two cows with rumen cannulae and duodenal re-entrance cannulae received in the first experiment (Ia and IIa) a conventional diet on the basis of a mixture of maize silage, hay and concentrated feed and after a three-week adaptation to isobutylidene diurea (IBDU)--276 g per animal and day--138 g IBDU with 3.865 mg 15N-excess as a single supplementation to their first meal. In the second experiment (IIa and IIb) after a 6-week break the same cows served a repeated experiment without IBDU adaptation. Irrespective of the adaptation, a re-increase of the 15N-labelling in the TCA-soluble N in the rumen could be proved between the 6th and the 8th hour after the intake of the isotopes, which resulted from the backflow of 15N to the rumen. In the duodenal digesta the maximum labelling of the TCA--soluble N-fraction appeared 12 hours after the intake of the isotopes. At that moment a labelling plateau began in the protein fraction, which lasted to the 36th hour. On an average of all 4 cows approximately 30% of the 15N taken in the TCA-precipitable fraction and 55 and 60% in the TCA-soluble fraction had passed the duodenum up to the 72nd hour after the beginning of the experiment. Up to the 72nd hour after the beginning of the experiment, approximately 15% were excreted in urine, approximately 16% in feces and approximately 7% in the milk. This shows that roughly one half of the 90% 15N-amount measured at its passage in the re-entrance cannula (related to the intake) was metabolised in the rumen at least twice, resp. after the first passage through the duodenum it originated from the intermediary metabolism (e.g. as amino acids and their incorporation as digestion secretions). Negative correlations could be ascertained between the pH-value of the rumen fluid and the 15N incorporation in the rumen proteins as well as 15N-excretion through the TCA-soluble and -precipitable quota of feces. An adaptation to IBDU is obviously not necessary.

[Isobutylidene diurea as an NPN source for ruminants. 1. Rumen fermentation, digestibility of the nutrients and microbial protein synthesis in dairy cows]. / Isobutylidendiharnstoff als NPN-Quelle für Wiederkäuer.

In 3 experiments 2 lactating dairy cows received a mixed ration consisting of 10 kg maize silage, 2.5 kg hay, 2.0 kg barley, 1 kg dried sugar-beet pulp, 1.5 kg maize starch, 0.5 kg sugar, 0.2 kg of a mineral-vitamin mixture and 0.08 kg non-protein nitrogen (NPN) per animal and day. The ration contained 8.3 kg dry matter, 5.1 kEFU cattle and 1.18 kg crude protein, 0.5 kg of which from NPN, and was given in equal shares twice a day. Urea (I) or isobutylidene diurea (IBDU), to which the animals were not adapted (II) resp. adapted (III), were the sources of NPN.IBDU proved to a be a very slow source of NH3 in the rumen. 2 hours after the intake of NPN 48 . . . 75, 5 . . . 9 and 5 . . . 12 mg NH3/100 ml could be detected from I to III. Up to the third hour the concentration of IBDU and urea increased in III, which is due to the slow distribution of the slowly soluble IBDU in the fluid digestaphasis. 12 hours after the feeding the level of IBDU and urea in III still amounted to 25 mg urea/100 ml, in I to 1 mg/100 ml only. In the first 3 hours after supplying the NPN the pH-value of I was more than 1 unit higher than that of II and III. There were no significant differences in the fermentation models between the variants, the concentration of volatile fatty acids was 12.6, 12.3 and 11.1 mmol/100 ml. In the stomachs the digestibility of the organic matter was 52, 51 and 54%, that of the crude cellulose 64, 62 and 66% and that of the starch 91, 93 and 98%. At the duodenum the passage rate of N was 87 . . . 93, 107 . . . 126 and 96 . . . 130% of the N-intake, that of NH3-N 6, 43 and 22 g per day and that of bacteria-N 61 . . . 76, 78 . . . 100 and 76 . . . 96% of the N-intake. 2.3 . . . 2.8, 2.6 . . . 3.2 and 2.1 . . . 3.1 g bacteria-N were formed per 100 g dry matter fermented in the rumen. In the intestines 55 . . . 61, 57 . . . 64 and 48 . . . 71% of the feed-N were available as non-NH3-N. The conclusion is that in comparison to urea and concerning IBDU, the rumeno-hepatic circulation plays a definitely bigger role for the N-supply of the rumen microbes and that the possibility of the better N-utilisation can be derived from that.

[Dynamics of 15N-isobutylidene diurea (IBDU) in sheep. 1. IBDU conversion in the digestive tract]. / Dynamik von 15N-Isobutylidendiharnstoff (IBDH) bei Schafen. 1. Mitteilung. Untersuchungen zum IBDH-Umsatz im Verdauungskanal.

Four Merino Landrace wethers averaging 47.6 kg body weight were adapted to a semi-synthetic diet containing as the only N-source 60 g of IBDU per day. After the adaptation phase, on the 1 st experimental day the IBDU of the morning feed was given in 15N-labelled form (701 mg 15N-excess). After 2 1/2, 7 1/4, 12 and 24 hours the experimental animals were killed without having been fed again. The comparison of the IBDU-concentrations in the content of the rumen bottom with the residual rumen content did not allow to draw conclusions regarding IBDU-sedimentation at the bottom of the rumen. For the 15N-decline in the rumen content, a relationship was established following y = 76.3 - 2.62 (r = 0.96) (see fig. 2). In the order of killing times the following 15N-IBDU amounts were retrieved (% of intake): I = 15.6%, II = 24.1%, III = 3.3% and IV = 3.6%. 7 1/4 hours after starting the experiment, 40% of the 15N-labelled material were found in the rumen in the form IBDU; after 12 hours it came to 10%. Except for sheep I, 15N-urea was not found but in small amounts. Only sheep I and III revealed IBDU-traces in the abomasum, but in the small intestine of all sheep 2 to 6% of the amount taken in. This fact is explained with the endogenous influx of IBDU from the blood. An additional experimental sheep provided with a ligature at the abomasum entry, revealed that IBDU is absorbed from the rumen and allowed to enter the individual segments of the intestine in small amounts.

[Long-term feeding of acetyl urea to dairy cows]. / Langfristige Fütterung von Azetylharnstoff an Milchkühe.

After an introductory survey of investigations dealing with the conversion of acetyl urea in the ruminant organism, a feeding trial using dairy cattle is described in which the effects of long-term acetyl urea feeding on the clinical picture and various performance parameters have been studied. Five Black-Pied cows of medium milk yield were fed a natural diet and received, over at least 14 months, a daily acetyl urea supplementation of 430 g (= 40 to 44% of the digestible crude protein). The clinical control, including the analysis of blood parameters, did not produce any deviation from normal. As to milk and butterfat yields, the experimental group reached results comparable to those of the control group. Over the entire experimental period the experimental group and the control averaged per cow and day of milking 11.1 and 11.3 kg FCM, respectively. The reproductive behaviour proved normal for all the cows under study. Postmortem findings of 4 cows revealed, among other things, chronic kidney alterations that cannot be safely exluded to be caused by the experiments. A stress over several months of two cows fed 850 g acetyl urea per day was not found to affect animal performance and health.

[In-vitro studies on the catabolism of acetyl urea in liver tissue]. / In vitro-Untersuchungen zum Azetylharnstoffabbau durch lebergewebe

In vitro-studies were carried out with hepatic tissue from freshley slaughtered cows using 14C acetyl urea (in which the urea-C-atom was labelled). Methods of thin-layer chromatography were used to investigate the process of acetyl urea degradation. The cows had not previouslybeen adapted to acetyl urea. The test mixtures used contained 3.3 mg or 20 mg acetyl urea per 100 ml of the homogenate. The pattern of acetyl urea degradation in these mixtures was investigated after 1 min, 3 mins, 10 mins and 30 mins. The degradation rates were found to be the same for both types of test mixtures. This indicated that a saturation of the substrate had not been accomplished, even when higher concentrations of acetyl urea were used. Supplementary addition of urease to the test mixture for decomposing the quantity of urea always produced did not alter the rates of acetyl urea degradation. From this it may be concluded that even under in vivo-conditions some urea will be liberated when acetyl urea passes through the liver.

[Isobutylidene diurea, a new NPN source for ruminants. 3. Excretion of isobutylidene diurea following feeding of N-15 isobutylidene diurea to lactating cows]. / Isobutylidendiharnstoff als neue NPN-Quelle für Wiederkäuer 3. Mitteilung. Untersuchungen zur IBDH-Ausscheidung nach Fütterung von 15N-IBDH an laktierende Milchkühe

2 experimental cows received isobutylidenedi urea added to a natural diet in amounts of 175 g (I) and 730 g (II) per day for a period of several weeks before the trial was started. On the 1st day of experiment the morning dose was labelled with 5.05 g of excess 15N. 8 hrs after the beginning of the trial of 15N level in the TCE soluble portion of blood plasma (TCE=trichloroacetic acid) increased and remained at an elevated level until the 36th hour of experiment. Similarly, the values for maximum urinary 15N concentrations were maintained for a prolonged period of time. Isobutylidenedi urea was excreted with the urine in rates related to its solubility. Only small percentages of the 15N intake were excreted in the TCE soluble portion of the milk (cow I: 0.03%; cow II: 0.05%). The 15N-labelling of milk protein provides evidence for the fact that nitrogen from IBDU is utilized for the synthesis of milk in the cows. The amount of urea in milk averaged 400 mg per litre. None of the milk samples tested contained IBDU.

[Isobutylidene-di-urea as a new NPN source for ruminants. 2. Metabolism of 14C-15N-isobutylidene-di-urea in sheep]. / Isobutylidendiharnstoff als neue NPN-Quelle für Wiederkäuer. 2. Mitteilung: Stoffwechsel von 14C-15N-Isobutylidendiharnstoff bei Schagen

2 male sheep (weighing 45 kg and 44 kg) were fitted with a ruminal fistula and a jugular vein catheter and received isobutylidendi-urea for a 42-day period of adjustment. The diet contained 25% starch, 23.8% glucose, 29.0% cellulose, 10.0% straw, 1.7% sunflower seed oil, 4.3% isobutylidendi-urea, 5.6% minerals and vitamins. Each animal received 60 g of isobutylidendi-urea in daily amounts of 1.4 kg of the ration-4.4% of the total dietary N came from the straw. At the begin of the trial each sheep received 30 g of 14C15N isobutylidendi-urea (C1-siobutyl labelling) administered as a suspension. The animals were then placedin respiration cages. The peak of specific 14C activity in the expired air (including ruminal gas) was observed 2 hrs after the beginning of the trial. 18--30 hrs after the beginning of the trial the highest level of 15N incorporation into the TCE (trichloroacetic acid) soluble fraction of the ruminal fluid was noted resulting from the reflow of urea via the rumeno-hepatic circulatory system in the rumen. A high concentration of 15N was shown to be present, for prolonged period, in the TCE soluble fraction of the ruminal fluid (up to the 30 hr of experiment). The 15N concentration in the blood plasma (TCE soluble portion) was found to increase reaching a peak value 23 hrs after administration of the isotope. The highest level of 14C activity in this fraction appeared 1 hr after isotope administration. The 15N incorporation into the protein fraction of blood plasma reached a constant high level between the 29th and 47th hr of experiment. The highest 15N concentrations in urine were noted after 1 day. 3.5% of the administered dose of 14C activity and 23% of the supplied amount of N were excreted in the urine. 20% of the total amount of 15N excreted in the urine could be detected as 14C isobutyl residues. An excess of between 0.05 and 0.17 atom% of the isotopes were found in muscular tissue and in different organs of the sheep when these were slaughtered on the 7th day of experiment (liver: 0.17%, kidneys: 0.14%, muscle: 0.05%, heart: 0.08%). The results obtained in the present trial clearly indicate that ruminants are able to utilize nitrogen from isobutyldi-urea.

[Isobutylene diurea as a new source of NPN for ruminants. 1. Nitrogen balance and plasma amino acid composition after feeding of isobutylene diurea to sheep]. / Isobutylidendiharnstoff als neue NPN-Quelle für Wiederkäuer

The paper first presents a survey of the existing literature where studies on the effects of isobutylidene diurea (IBDH) as NPN source for ruminants are discussed. Following this the authors discuss their own experiments on IBDH turnover. IBDH showed no toxi cation when tested in toxicity studies with rats which were carried out under standardized conditions. Within the framework of metabolism trial 4 growing male sheep (average liveweight: 30 kg) were fed a semisynthetic diet containing IBDH as sole N source. Each animal received 60 g IBDH per day. The average value for the apparent N digestibility was found to be 77.6%, the percentage for the average N ballance was 27.6%. The blood of the sheep was investigated, on a comparative basis, for the behaviour of free amino acids after the administration of an experimental semisynthetic diet containing IBDH or extracted soya bean meal as sole N source. The use of IBDH produced a higher concentration of free amino acids and a five-fold increase if urea concentrations in the blood plasma but reduced the Asp, Cys and Tyr levels when compared with the feeding of extracted soya bean meal. Similarly, IBDH supplementation increased the relative proportions of Gly, Lys, and His in blood plasma but reduced those of Asp, Val and Tyr. A positive relationship between the rate of IBDH hydrolysis and the decrease in pH was found in experiments studying the hydrolysis behaviour of IBDH at pH values from 1-7.

[Excretion of acetyl urea in milk following oral 14C-acetyl urea administration to dairy cows]. / Untersuchungen zur Ausscheidung von Azetylharnstoff über die Milch nach oraler 14C-Azetylharnstoffgabe an Milchkühe

2 experimental cows were fed acetyl urea several weeks before the trial was started. The first cow received a daily amount of 200 g and the second cow 855 g. On the first day of experiment both cows were given 5 mCi of 14C acetyl urea intraruminally. Up to 6 hrs after the beginning of the experiment acetyl urea in blood plasma was shown to contain a higher proportion of 14C activity than urea. 0.21 g urea and 0.18 g acetyl urea were contained in 1 kg of milk from cow No 1 while 1 kg of milk from cow No 2 contained 0.18 g urea and 0.12 g acetyl urea. The feeding of acetyl urea to dairy cows is not recommended on the basis of the fact that any further contamination of human nutrition with foreign substances should be possibly avoided.

[Metabolism of 15N-14C-acetylurea in the sheep]. / Der Umsatz von 15N-14C-Azetylharnstoff beim Schaf

3 male sheep (phi 48.3 kg) were fed a semisynthetic diet containing acetyl urea as sole protein source and 15N-14C labelled acetyl urea (urea-C labelled) by intraruminal tube. A half life period of 4 hrs was established for the removal of labelled acetyl urea from the TCE-soluble portion of the ruminal fluid. The degree of 14C labelling in ruminal proteins was very low whereas the extent of 15N labelled protein synthesis was quite marked reaching a maximum between the 18th and 24th hour of experiment. The steepest rise of 15N incorporation into ruminal proteins was found to occur between 8 to 12 hrs after start of the experiment, i.e. at the time of peak level of 15N returned from 15N urea via the rumino-hepatic circulation. 23.3% of the amount of 14C activity administered (mean of all 3 experimental animals) was excreted through respiration. The curve patterns of both isotopes in the TCE soluble portion of the ruminal fluid were similar to that of the degasified TCE soluble portion of the blood blasma. At the peak time (8 hrs) a concentration of the nitrogen isotope of about 4 atom% excess of 15N was observed. The level of 14C labeling in blood plasma proteins was insignificant when compared with that of 15N labelling. The ratio at the peak time was 1:10; the same ratio was found for ruminal proteins. From this it can be concluded that the process of labelling of blood plasma proteins proceeds mainly through microbial protein synthesis. Sheep I and III excreted an average of 60.6% of 14C activity and 57.0% of the administered excess of 15N in the urine. 6 hrs after the beginning of the experiment 81% of the amount of urinary 14C activity was found to occur as acetyl urea; after 48 hrs this amount had decreased to 50%. All experimental sheep excreted a urinary sediment consisting mainly of acetyl urea. The level of faecal 14C excretion (1.4%-2.9% of the amount administered) was considerably lower than that of 15N excretion (9.1%--15.6% of the administered dose). The TCE soluble fraction of the faeces contained up to 2% of the 14C dose and 3% of the 15N dose. The true digestibility data of 15N from 15N acetyl urea varied between 96.4% and 98.2%. An average of 40.9% was obtained for the 15N balance over the 7-day trial period.

[Studies on the 14C-15N-acetamide turnover in sheep. 2. Studies on 15N turnover and comparative studies on the 14C turnover]. / Untersuchungen zum Umsatz von 14C-15N-Azetamid bei Schafen 2. Mitteilung Untersuchungen zum 15N-Umsatz und vergleichende Betrachtungen zum 14C-Umsatz

Three fistula sheep with average weights of 52.2 kgs were given 37.9 g of 15N and 14C labelled acetamide (= 1.09 mg 15N' and 0,95 mCi14C) which were administered directly through the fistula. The half-life period of 15N retention in the ruminal fluid (TCE soluble portion) was found to be 4 hrs. 18 hrs after 15N administration increasing amounts of 15N were carried back to the rumen by way of the rumino-hepatic circulation. The 15N concentration in the blood (TCE soluble portion) rapidly increased up to a peak value and, from 3 hrs after isotope administration, the 15N concentration was found to decline continuously, with a slight discontinuation at about the 10th hr of experiment. The rate of 15N incorporation into the protein fraction (TEC soluble portion) of the blood was delayed by 4 hrs, relative to the rate of 15N incorporation into ruminal proteins. An average of 43.1% of the administered amount of 15N was excreted in the urine within 7 days. Up to the 4th day of experiment the half-life period of urinary 15N excretion was 19 hrs. An average of 15% of the administered total amount of 15N was excreted in the faeces. In this process, the peak values in both TCE fractions were observed to occur on the 2nd day of experiment. The proportion of isotope in the TCE soluble fraction was found to increase continuously compared with the total amount of the isotope excreted in the faeces. Isotope concentrations between 0.03 and 0.13 atom% of surplus 15N were found in organ and muscle tissues of a sheep that had been slaughtered 7 days after administration of the isotope. The results obtained are discussed on the basis of comparisons made with the analogous behaviour of 14C activity.

[Studies on the 14C-15N-acetamide turnover in sheep. 1. Studies on the 14C turnover]. / Untersuchungen zum Umsatz von 14C-15N-Azetamid bei Schafen Mitteilung Untersuchungen zum 14C-Umsatz

4 male sheep (average weight: 53.5 kgs) were fed a semisynthetic diet containing acetamide as sole source of nitrogen. At the beginning of the trial twin-labelled 15N-14C-acetamide was administered by way of a ruminal fistula. The curve pattern of 14C activity in the TCE-soluble fraction of the ruminal fluid showed a synchronous behaviour in all animals beginning at 3 hours after the beginning of the trial. A half-life of 2 1/2 hours for the rate of absorption of 14C acetamide and deaminated 14C acetate was established from the decline in 14C activity observed in the TCE-soluble fraction of the ruminal fluid. The peak level of 14C labelling in ruminal proteins was reached after 6 hrs. The specific 14CO2 activity in respiratory air reached its maximum level after 4 hrs, and was then found to decline continuously. 56% of the administered amount of 14C was excreted over a period of up to 50 hrs after beginning of the trial. The very fact that the peak level of 14C activity was observed to appear in the TCE-soluble fraction of the blood plasma as early as after 1 hr seems to indicate that acetamide is also absorbed through the ruminal wall. The half-life of decline in the 14C activity of this fraction was 5.7 hrs. Analysis by thin layer chromatography showed that 75% of this amount of activity is present in 14C acetamide. The rate of 14C incorporation into blood plasma proteins reached a plateau region after 21 hrs, which was also maintained on the 2nd day of the experiment. 6.5% of the administered amount of 14C activity was excreted in the urine until the 7th day of experiment. 76.6% of the amount of urinary 14C activity excreted within a period of 48 hrs were voided as 14C acetamide. 3.8% of the administered amount of 14C activity was excreted with the faeces within the first 6 days of experiment.