Endogenous N-losses in piglets estimated by a [15N]-isotope dilution technique: effect of xylanase addition to a wheat and rye based diet.

The nitrogen pool of piglets weighing 19.4 +/- 1.4 kg at the beginning of the experiment was labeled with an oral application of ([15N]H4)2SO4 (1.26 [15N]-atom percent excess of dietary N) over a period of 7 d. The labeling period was followed by an equilibration period of 7 d without feeding the labeling compound. The two experimental diets were based on wheat (53%) and rye (25%) and were fed either with or without a xylanase containing enzyme preparation over both experimental periods. Additionally, diets were supplemented with an indigestible marker during the 2nd period of the experiment to allow the calculation of endogenous N-losses in subsequent segments of the digestive tract of the pigs. These endogenous N-losses were estimated at the end of the experiment by analyzing feces, ingesta and urine for [15N]-enrichment assuming that [15N]-enrichment of urine represents the [15N]-enrichment of the precursor pool. Endogenous N-losses were not significantly affected by xylanase addition at any measurement site (stomach, 3 sections of the small intestine, total digestive tract). Endogenous N-proportions of total nitrogen amounted on average for the six pigs to 42 +/- 11% and 56 +/- 5% at the last section of the small intestine and over the whole digestive tract, respectively, which corresponded to endogenous N-losses of 2.8 +/- 1.3 g N/kg DM and 2.0 +/- 0.3 g N/kg DM, respectively.     

Effects of dietary fat type and xylanase supplementation in rye containing diets on energy metabolism in male broilers

Xylanase supplementation of rye-based diets which contained 10% beef tallow was shown to markedly improve the digestibility of fat whereas the enzyme effect in diets containing 10% soya oil was much less pronounced (Dänicke et al. 1997b). Such interactions between fat type and xylanase supplementation have also been reported for wheat–rye-based diets (Langhout et al. 1997) and wheat-based diets (Allen et al. 1997) and were attributed mainly to the fatty acid composition of different types of fat and to changes in digesta viscosity caused by soluble pentosan. The apparent metabolizable energy, N-corrected (AME_N) contents of such diets were affected in a similar manner suggesting that energy metabolism is also influenced by xylanase supplementation and the type of dietary fat. However, changes in the metabolizability of gross energy does not necessarily indicate whether the efficiency of metabolizable energy (ME) for energy gain is changed nor if different proportions of ME are used for maintaining an energy equilibrium, i.e. ME maintenance requirement. In addition, studies suggest that both dietary fat level and fat type might exert effects on the efficiency of utilization of ME for energy retention (Carew and Hill 1964; de Groote et al. 1971; Fuller and Rendon 1979; Brue and Latshaw 1985). Hence, the aim of this study was to investigate the partitioning of ME between maintenance needs and energy retained as protein and as fat when feeding rye-based diets. The diets contained either soya oil or beef tallow and were either unsupplemented or xylanase-supplemented.     

Effects of dietary fat type, pentosan level and xylanase supplementation on digestibility of nutrients and metabolizability of energy in male broilers.

A complete two by two by four factorial design was used to examine the main effects of dietary fat type (10% soya oil or 10% beef tallow), xylanase supplementation (with or without Avizyme 1300 at 1 g/kg diet) and pentosan level (7.7 g/kg, 11.0 g/kg, 14.3 g/kg and 17.6 g/kg soluble pentosans, respectively, by varying wheat/rye proportions) as well as their interactions on intestinal chyme conditions, nutrient digestibility and nutrient utilization in male broilers. Nutrient digestibilities for the total digestive tract and at various sites of small intestine were measured during the period from day 18 to 20 of age and at day 21 of age, respectively, using a marker technique. Jejunal and ileal supernatant viscosity increased in an exponential manner as dietary pentosan concentration was increased. This increase was more pronounced in tallow fed birds but was also found in enzyme treated groups albeit at a much lower level. Xylanase activity was still detectable in the ileum of birds fed enzyme supplemented diets but its activity was found to decrease as dietary pentosan content increased. Digestibility of crude protein and that of some amino acids at the terminal ileum was decreased as dietary pentosan content was increased and significantly improved by xylanase addition. No fat effect and no interactions were detected at this site. In contrast, measurements made over the whole gastrointestinal tract showed significantly lower protein and amino acid digestibility values for tallow fed birds, and significant higher enzyme effects especially in diets with higher pentosan concentrations. Nitrogen-corrected apparent metabolizable energy (AMEN) content and net protein utilization decreased with increasing dietary pentosan content and were significantly improved by xylanase addition and were lower in tallow fed birds. Again, xylanase effects were found to be more pronounced for tallow fed birds and at higher pentosan concentrations.     

Effects of dietary fat type and non-starch-polysaccharide-hydrolysing enzyme addition to rye-based diets on muscle protein turnover in broilers

1. Muscle protein turnover was measured in broilers fed on rye-based diets containing either beef tallow (T) or soybean oil (S) at an inclusion rate of 100 g/kg. Each of these diet types was tested either in the absence (S[-], T[-]) or presence (S[+], T[+]) of a xylanase-containing enzyme preparation. Protein turnover was measured in gastrocnemius muscle (GM) and pectoralis major muscle (PM). 2. Fractional rate of protein synthesis (FSR) was measured by the large dose technique using [15N]-labelled phenylalanine whereas fractional protein growth rate (FGR) was estimated by regressing tissue protein content over time. Fractional breakdown rates (FBR) were calculated by the difference between FSR and FGR. 3. In PM, FSR (%/d) was 22.1, 23.4, 21.5 and 24.4 in groups S[-], S[+], T[-] and T[+], respectively, and FBR (%/d) was 8.3, 9.8, 4.5 and 10.8 with the xylanase effect being significant. The FGR of 17.0%/d calculated for the broilers fed on the T[-] diet tended to be higher than for the other groups (13.6 to 13.8%/d). No significant effects were detected for these parameters in the GM. 4. The absolute amounts of protein which were synthesised daily and accreted in both muscles were significantly higher with xylanase supplementation in both fat type diets but at a significantly higher level when soybean oil was the dietary fat type. 5. The observed effects on protein turnover have to be seen in the context of an overall adverse effect of dietary soluble pentosans from rye in combination with tallow on physico-chemical chyme conditions, digestion and absorption of energy and nutrients and tissue-specific metabolic changes.     

Incorporation of nitrogen-15 from dietary [15N] diammonium citrate into amino acids of liver and muscle proteins in germfree and specific-pathogen-free neonatal pigs

Incorporation of 15N from dietary [15N]diammonium citrate ([15N]DAC) into amino acids isolated from hydrolyzed tissue proteins was investigated in the presence or absence of intestinal flora in neonatal pigs. The 15N was incorporated into all of the essential and nonessential amino acids from liver and muscles in one of two germfree pigs and two specific-pathogen-free pigs which were killed on the 5th day after the administration of [15N]DAC. But, a higher 15N concentration than natural abundance of 15N was not detected in histidine, lysine, and threonine from these tissues in another germfree pig killed the next day. Nitrogen transfer from DAC into all amino acids, including these three essential amino acids, may be possible in the specific-pathogen-free pig and even in the germfree pig.     

The effect of dietary fish oil soapstock on the performance,carcass fat and flavour of broilers 1

Three hundred and thirty six male broilers were fed on diets containing two levels (2% and 4%) of either acidulated soybean oil soapstock (SOS), acidulated fish oil soapstock (FOS), or a combination of the two. Some of the replicates were changed from FOS diets to diets containing 4% SOS at 5 or 6 1/2 weeks of age.

Dietary FOS was slightly, but significantly, inferior to SOS with regard to live performance, apparently due to an adverse effect on food intake. All birds fed on FOS were unpalatable due to a pronounced “fishy” flavour, thigh meat being more objectionable than breast meat and cooked broth more than roasted meat. About 3 to 4 weeks after transfer to SOS diets, the broilers were acceptable.

Both soapstocks contained over 65% free fatty acids, but their fatty acid composition differed, with the FOS containing more C₁₂ to C₁₆ saturated fatty acids, palmitoleic acid and the typical long‐chain polyenoic fatty acids, but much less linoleic acid. These patterns were reflected in the total dietary lipids and in the abdominal adipose tissue. After the type of dietary soapstock was altered, there was a gradual change in the composition of body fat, which, after about 3 weeks, approached the fatty acid pattern of the birds fed on a diet containing 4% SOS throughout their growing period.     

The metabolic use of energy from dietary fat in broilers is affected by fatty acid saturation

1. Two experiments were performed to evaluate the effect of dietary fat on performance and fat and protein accretion in broiler chickens according to the degree of saturation. 2. The first experiment was designed to test 2 sources of dietary fat and 3 levels of dietary energy using a factorial (2x3) experimental design. The foods were formulated to maintain a constant ratio of energy to protein (and other nutrients). There were no significant differences in weight gain, intake, final body weight or food to gain ratio between broilers fed on diets differing solely in the degree of fat saturation. Broilers fed on diets containing animal fat showed higher whole-body fat retention (P=0.02) and lower protein accretion (P=0.03) than those fed on diets containing vegetable oils. 3. In the second experiment, only 1 concentration of fat (tallow, lard or sunflower oil) was incorporated into the experimental diets, providing different energy to protein ratios. The carcase protein content was not affected by dietary fat source, while total fat accretion (P=0.01) and energy retention (P=0.14) were highest in broilers fed on a diet containing tallow. 4. The findings suggest that the degree of saturation of dietary fats affects their metabolic use and fat accumulation in broiler chickens.     

Stability of abdominal fat and meat of broilers: The interrelationship between the effects of dietary fat and vitamin E supplements 1

1. The effect of graded increments of α‐tocopheryl acetate (ATA), in diets containing various fat supplements at different concentrations, on tissue a‐tocopherol (TOC) content and on the stability of abdominal fat and meat of broilers was determined.

2. Plasma, liver and adipose tissue TOC content increased markedly as dietary ATA concentrations rose. The type or amount of fat supplementation had no consistent effect on tissue TOC content; however, these factors affected the degree of saturation of carcass fat.

3. Stability of abdominal fat and meat was little affected by the degree of saturation of carcass fat in the absence of dietary ATA. The latter significantly improved stability of these tissues in broilers having relatively saturated carcass fat, whereas its beneficial effect was rather limited as the degree of unsaturation of carcass fat increased.     

Endogenous nitrogen metabolism in 15N-labeled swine. 1. Course of 15N-labeling and 15N excretion in urine and feces under 4 different diets

Four male castrated pigs (55-65 kg) either received a wheat--fish meal diet (1 and 2) or a wheat--horse bean diet (3 and 4) without straw meal supplement (1 and 3) or with a supplement of 20% DM partly hydrolysed straw meal to the DM of the ration (2 and 4). In order to investigate whether a 15N-labelling of the pigs is also possible with a protein excess in the ration, the animals 1 and 2 received 24.8 g and the animals 3 and 4 = 11.6 g crude protein/kg0,75 live weight. During a 10-day 15N-labelling 385 mg 15N-excess (15N') per kg0,75 were applied in a mixture of ammonia acetate and ammonia chloride in the feed. During the period of 15N-labelling the following quotas of the applied 15N-amount were incorporated: 1 = 10.2%, 2 = 7.2%, 3 = 18.7%, 4 = 14.4%. 15N-excretion in both TCA fractions of faeces showed a highly significant positive correlation to the increasing content of crude fibre in the 4 diets. The immediate 15N-incorporation into the TCA-precipitable fraction of faeces (from the 2nd of the beginning of the 15N-application onwards) proves that 15N enters the large intestine endogenously (probably as 15N-urea) and serves bacterial protein synthesis. Three days after the last 15N-application the pigs were killed. The following values of atom-% 15N' could be determined in the TCA-precipitable blood plasma and in the TCA-precipitable fraction of the liver: 1 = 0.18 and 0.19 resp., 2 = 0.22 and 0.27 resp., 3 = 0.22 and 0.23 resp. and 4 = 0.24 and 0.26 resp. The other examined organs and tissues showed smaller differences between the test animals. The following atom-% 15N' were measured in the TCA-precipitable fractions on an average of the 4 test pigs: kidney = 0.20, pancreas = 0.18, intestinal wall tissue, duodenum = 0.18, jejunum (beginning) = 0.17, jejunum (end) = 0.15, ileum = 0.15, caecum = 0.16, colon (beginning) = 0.15, colon (middle) = 0.14, colon (end) = 0.13, stomach (cardia) = 0.11, stomach (fundus) = 0.12, spleen = 0.13, heart = 0.12, skin = 0.07 and skeleton muscles = 0.06. The results show that the 15N-labelling of tissues and organs of pigs is also possible at a high level of protein supply by means of an oral application of 15N ammonia salts.     

Assessment of body fat in the pony: part II. Validation of the deuterium oxide dilution technique for the measurement of body fat

Reasons for performing the study: Excessive accumulations or depletions of body fat have been associated with increased morbidity and mortality in horses and ponies. An objective, minimally‐invasive method to accurately quantify body fat in living animals is required to aid nutritional management and define welfare/performance limits. Objectives: To compare deuterium oxide (D₂O) dilution‐derived estimates of total body water (TBW) and body fat with values obtained by ‘gold standard’ proximate analysis and cadaver dissection. Hypothesis: D₂O dilution offers a valid method for the determination of TBW and body fat in equids. Methods: Seven mature (mean ± s.e. 13 ± 3 years, 212 ± 14 kg, body condition scores 1.25–7/9), healthy, Welsh Mountain pony mares, destined for euthanasia (for nonresearch purposes) were used. Blood samples were collected before and 4 h after D₂O (0.11–0.13 g/kg bwt, 99.8 atom percent excess) administration. Plasma was analysed by gas isotope ratio mass spectrometry following filtration and zinc reduction. After euthanasia, white adipose tissue (WAT) mass was recorded before all body tissues were analysed by proximate chemical analyses. Results: D₂O‐derived estimates of TBW and body fat were strongly associated with proximate analysis‐ and dissection‐derived values (all r²>0.97, P≤0.0001). Bland‐Altman analyses demonstrated good agreements between methods. D₂O dilution slightly overestimated TBW (0.79%, limits of agreement (LoA) ‐3.75–2.17%) and underestimated total body lipid (1.78%, LoA ‐0.59–4.15%) and dissected WAT (0.72%, LoA ‐2.77–4.21%). Conclusions and potential relevance: This study provides the first validation of the D₂O dilution method for the minimally‐invasive, accurate, repeatable and objective measurement of body water and fat in living equids.     

15N-leucine and 15N-isoleucine isotope dilution techniques versus the 15N-isotope dilution technique for determining the recovery of endogenous protein and amino acids in digesta collected from the distal ileum in pigs.

Twelve gilts, with an average initial BW of 38 kg, were fitted with simple T-cannulas at the distal ileum and two catheters in the external jugular veins. The animals were fed twice daily (0800 and 2000) 700 g of one of four diets containing either soybean meal, canola meal, wheat, or barley as the sole protein source. 15N-leucine was infused continuously for 9 d at a rate of 40 mg/kg of BW daily via one of the jugular catheters. Blood samples were taken during feeding. Ileal digesta samples were collected continuously for 24 h on d 7 and 9 of the infusion period. 15N-enrichment excess in leucine and isoleucine in the trichloroacetic acid (TCA)-soluble fraction of blood and in digesta were measured using single-ion monitoring gas chromatography-mass spectrometry. Assuming that the 15N-enrichment excess in leucine and isoleucine in the TCA-soluble fraction of the blood is similar to that in endogenous protein secreted into the digestive tract and that the amino acid composition of endogenous protein is constant, the contribution of endogenous to total protein in ileal digesta was calculated using the 15N-isotope dilution technique for leucine and isoleucine, respectively. These contributions were much smaller for the 15N-leucine than for the 15N-isoleucine isotope dilution technique: 7.1 to 11.0 vs 21.8 to 24.9 g of protein/kg of DM intake. The values obtained with the 15N-isoleucine isotope dilution technique were close to those obtained with the 15N-isotope dilution technique as described in a previous publication.     

Effect of dietary fatty acid pattern on growth, body fat composition and antioxidant parameters in broilers

The effects of dietary fat supplementation on performance, fatty acid (FA) composition of tissues and antioxidant defence system of broilers were studied. Male broilers were placed in 20 floor pens (60 broilers per pen). The broilers were fed by diets with added different energy sources: lard (L); sunflower oil (SFO); soybean oil (SBO); and linseed oil (LSO). The treatments did not modify significantly growth performance and feed intake of the broilers. There was no effect of dietary FA pattern on reduced glutathione level and glutathione peroxidase activity of plasma, erythrocyte and liver samples. However, higher PUFA content of the diet resulted in a significant increase in malondialdehyde level of erythrocytes and liver. The broilers fed LSO diet more effectively maintained their antioxidant status with enhanced plasma radical scavenger capacity. FA composition in tissues reflected the FA pattern of the diets, although proportion of FAs with four or more double bonds was metabolic specific. LSO diet increased the level of C18:3, C20:5 and C22:6 in tissue lipids in relation to L, SFO and SBO diets. Significantly increased plasma radical scavenging capacity in concert with the enhanced C20:5 and C22:6 proportion in liver and muscle during LSO feeding indicate metabolic changes to counteract the oxidative injury. This may be related to the compounds produced after different biochemical pathways of n-6 and n-3 FAs.     

Effect of dietary concentrations of fat and energy on fat deposition in broilers divergently selected for high or low abdominal adipose tissue

1. Fat deposition in abdominal, mesenterial, sartorial and gizzard adipose tissues (AT), liver, breast muscle, skin and carcase was studied in male broilers, selected for high (HF) and low (LF) abdominal fat and fed on diets differing in energy density and total fat content. 2. There were no significant differences in body weight in the experimental groups. The relative weight (g/kg body weight) of the dissected adipose tissues was higher in HF than in LF birds. Fat concentration in the AT (sartorial excepted), skin and body was higher in the HF compared with the LF birds. The lines did not differ significantly in liver and breast muscle fat content. 3. Abdominal AT was affected by selection or dietary fat more than other AT and total body fat. 4. In the HF birds increasing energy density from 12.3 to 13.4 MJ/kg (dietary fat kept constant: 5.46 g/MJ) significantly increased the weight of the abdominal, mesenterial and sartorial AT. Increasing dietary fat (at both energy densities) decreased the weight of the AT, whereas increasing both energy and fat did not affect it. In the LF birds, similar but milder and insignificant trends were observed. It is suggested that this interaction has biological significance.     

Relationship between serum leptin immunoreactivity and body fat mass as estimated by use of a novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats

OBJECTIVE: To validate a recently developed commercially available leptin radioimmunoassay (RIA) for use with feline serum and evaluate the relationship between serum leptin concentrations and body fat mass in domestic cats. ANIMALS: 19 sexually intact male specific-pathogen-free domestic cats that weighed 3.8 to 7.1 kg and were 1.1 to 3.5 years old. PROCEDURE: Specificity for feline leptin was evaluated by use of gel filtration chromatography and reverse-phase high-performance liquid chromatography fractionation of serum. Body fat mass was determined by use of the deuterium oxide (D2O) dilution method. Serum water D2O enrichment was measured by use of gas-phase Fourier transform infrared spectroscopy. RESULTS: Body fat mass and percentage body fat ranged from 0.3 to 2.3 kg and 7.5 to 34.9%, respectively. Serum leptin concentrations were lower in the unfed versus the fed state and ranged between 1.6 and 4.9 ng/ml human equivalent (HE); mean +/- SD value was 2.9 +/- 0.2 ng/ml HE. Leptin concentrations increased with increasing body fat mass and percentage of body fat. CONCLUSIONS: Leptin is in the serum of domestic cats in free (> 78%) and apparently bound forms. The relationship between body fat and serum leptin concentration was similar to that observed in humans and rodents and indicative of a lipostatic role for leptin in cats. Cats that have an overabundance of body fat appear to be less sensitive to the weight-normalizing action of leptin than cats of ideal body condition.     

Endogenous nitrogen metabolism in 15N-labeled swine. 3. Endogenous excretion of 15N- and 14C-labeled secretions following a 14C-leucine injection

Four pigs (59-65 kg live weight) were labelled over a period of 10 days with 15N in the feeding of a fishmeal diet (1), a fishmeal diet + partly hydrolysed straw meal (2), a horse bean diet (3) and a horse bean diet + partly hydrolysed straw meal (4). After a 24-hour fasting the animals were provided with simple cannulae in the upper part of the small intestines. After a fasting period of 24 h all four pigs received a 14C-leucine injection and the cannula secretion was collected in the subsequent 24 h. After the feeding of the diets without straw meal supplement (1 and 3) there were distinct differences in the secretion in comparison with the feeding with straw meal supplements (2 and 4) despite the long fasting period (48-72 h). 14C-activity could already be detected in the TCA-precipitable fraction of the secretion after 3-6 min of the injection in 1 and 3 but only 20 to 25 min after the 14C-leucine injection in 2 and 4. The specific 14C-leucine activity of the TCA-soluble fraction of the secretion was, after the straw meal supplementation to the fish meal diet, 15 times higher 25 min after the 14C-leu-injection, 25 times higher after 70 min, 36 times after 2 h and 1.8 times after 4 h than without straw meal supplementation. For all four diets a specific correlation (r = 0.96) could be ascertained between the increase of 14C-activity/mg N in the TCA-soluble fraction and the increasing crude fibre content in the diet between 25 and 180 min after the injection. Furthermore, a distinctly decreased N-secretion/h could be ascertained (correlation coefficient r = 0.84) with the increasing crude fibre content in the diet. The influence of the crude fibre on the parameters mentioned is seen in the changed osmotic conditions in the secretion, which may be caused by the changed regulation by hormones of the gastro-intestinal tract. The atom-% 15N' in both TCA-fractions of the secretion underwent big rhythmic variations, which is explained by different ratios of the components pancreatic juice, bile, and intestinal juice.     

Threonine incorporation in tissues of growing broiler chickens using L-[15N] threonine

Most amino acid requirement trials appear for whole-body responses, but there is little information concerning amino acid incorporation in individual tissues, which may vary according to the age. L-[¹⁵N] threonine was used to evaluate its incorporation rate and distribution among broiler tissues in different ages. Seventy-two male broiler chickens were distributed into three different phases: starter (4 to 9 days old), grower (18 to 23 days old) and finisher phase (32 to 37 days old). L-[¹⁵N] threonine was added on balanced diets, and birds were fed for five days in each phase. Enriched samples of breast muscle, feathers, liver, jejunum and plasma were collected at 0, 6, 12, 24, 48, 72, 96 and 120 hr after fed birds with the tracer in each phase. In the tissues were analysed dry matter, nitrogen and stable nitrogen. The ¹⁵N isotope abundance according to the time was fitted into exponential or linear equations using a same intercept. The ratio of the steepness or slope coefficients was determined to compare the L-[¹⁵N] threonine incorporation according to the age. In addition, L-[¹⁵N] threonine mass balances were performed to assess the L-[¹⁵N] threonine distribution among the evaluated tissues. Except for feathers, the L-[¹⁵N] threonine incorporation rate decreased with ageing. Taking into account the L-[¹⁵N] threonine distribution in the tissues, only in the jejunum was not observed an increase as the broiler grew. The L-[¹⁵N] incorporation varied in each tissue and according to the age of the broiler chickens. These outcomes could be useful to comprehend changes in amino acid requirements tissue-specific according to age.     

稻壳稀释日粮对鹅肝脏和肌肉脂肪含量的影响

本试验旨在研究稻壳稀释日粮对鹅屠宰性能和脂肪含量的影响.选用140日龄体重相近的健康扬州鹅公鹅96只,随机分成A、B、C、D共4组,每组4个重复,每个重复6只,A组为对照组,饲喂基础日粮(DE,11.13 MJ/kg;CP,15.86%;CF,5.6%),B、C、D组为试验组,试验日粮分别用稻壳替代20%、40%、60%的基础日粮,3周后,每组取8只(每个重复2只),测定其屠宰性能以及肝脏和肌肉的脂肪含量.结果表明:(1)B组肝脏和腿肌脂肪含量最高,其中肝脏脂肪含量显著高于C、D组(P＜0.05),C组胸肌脂肪含量最高;(2)D组体重极显著低于其他3组(P＜0.01),腿肌重显著低于B、C组(P＜0.05);(3)各组之间屠宰率差异不显著(P＞0.05).由此可见,稻壳替代基础日粮的比例不高于40%,对140日龄公鹅生长性能无显著影响,并能够在一定程度上改善肌肉品质.     

Effect of colostomy on the occurrence of dietary [15N]urea in intestinal contents,blood, urine and tissues in chickens fed a low protein diet plus urea

1. The occurrence of ¹⁵N was examined in excreta for 10 h, and in intestinal contents, blood and tissues at 10 h after [¹⁵N]urea was fed to conventional and colostomised cockerels.

2. Total‐¹⁵N excretion and ¹⁵N‐balance in control chickens were 18.88 and 44.79 mg/kg body weight/10 h), respectively. The former was increased and the latter was decreased by colostomy by 10.75 mg (P<0.01).

3. Amounts of [¹⁵N]urea, [¹⁵N]ammonia and [¹⁵N]uric acid excreted by control birds were 13.78, 3.90 and 0.18 mg/kg body weight/10 h or 0.73, 0.21 and 0.01 of the total‐¹⁵N excreted respectively.

4. The [¹⁵N]urea, [¹⁵N]uric acid and total‐¹⁵N excreted were all increased after colostomy but [¹⁵N]ammonia was decreased (uric acid P<0.05, others P<0.01). The increase in total‐¹⁵N was mostly accounted for by [¹⁵N]urea.

5. Colostomy resulted in significantly less total‐¹⁵N in the contents of the whole intestine (P<0.01), less total‐¹⁵N, [¹⁵N]ammonia and [¹⁵N]urea in the contents of the co!o‐rectum (P<0.01) and less total‐¹⁵N and [¹⁵N]urea in the contents of the upper intestine (P< 0.05); it did not affect any in caecal contents.

6. [¹⁵N]Urea in blood, liver and kidney (blood P<0.01, others P< 0.05), and [¹⁵N]glutamine amide (P< 0.05) and [¹⁵N]uric acid (P< 0.01) in blood were significantly decreased after colostomy.

7. The results support the hypothesis that most of the dietary urea is utilised as the result of a back‐flow of ureteral urea into the caeca where it is rapidly converted into ammonia which is then metabolised to other compounds.