Yutaka Karasawa

Significant role of the nitrogen recycling system through the ceca occurs in protein-depleted chickens.

This study focuses on the role of the ceca in nitrogen nutrition in chickens (Gallus domesticus). Urea is a very good nitrogen tracer for these studies. Little urea is synthesized by chickens due to the absence of carbamyl phosphate synthetase, an essential enzyme initiating the urea cycle. Urea is utilized by chickens when crystalline amino acid diets low in nonessential nitrogen or diets containing low concentrations of intact protein are fed, and most ureolytic activity is found in the ceca. Dietary urea was absorbed intact from the upper intestine of the chicken. The absorbed urea was excreted into ureteral urine that refluxed from the cloaca into the colon and ceca where urea was degraded to ammonia. Presumably the ammonia was incorporated into amino acids by cecal microorganisms and some urea, amino acids and proteins were absorbed from the ceca. These were utilized by the chickens. A beneficial role of ceca in the nitrogen metabolism in the chicken is, therefore, conservation of urinary nitrogen in protein-depleted chickens.

Role of caeca in the nitrogen nutrition of the chicken fed on a moderate protein diet or a low rotein diet plus urea

1. A study was carried out to investigate whether the back-flow of urine into the caeca benefits the nitrogen economy of adult cockerels fed on a diet containing 100 g protein/kg and when dietary urea is absorbed, excreted into urine and utilised. 2. No significant effects of colostomy on nitrogen utilisation were observed in chickens fed on 100 g/kg protein diet, whereas colostomy was highly effective in decreasing it in chickens on a diet containing 50 g protein/kg plus urea (P < 0.05). 3. Nitrogen utilisation in conventional birds was significantly less when a diet of moderate protein content was fed than when a low protein diet plus urea was fed, but the opposite effect was seen with colostomised birds (P < 0.05). 4. Colostomy increased urea excretion (nitrogen/kg body weight/day) from 4 to 9 mg in chickens fed on the moderate protein diet, but greatly, from 45 to 182 mg, in those fed on the low protein diet plus urea (P < 0.05). 5. Blood urea concentration increased by about 20 mg per 100 ml in 3 h, a value which was maintained up to 6 h but which returned to the prefeeding concentration at 24 h; both control and colostomised chickens on the low protein diet plus urea responded similarly. 6. After feeding urea, half the daily excretion of urea was observed to occur within 6 and 9 h, respectively, in control and colostomised chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of caecectomy on growth, moisture in excreta, gastrointestinal passage time and uric acid excretion in growing chicks.

1. The effect of caecectomy on nitrogen utilisation and excretion was examined in growing chicks fed on a commercial diet. 2. Caecectomy had no significant effect on food intake or body weight gain. 3. Caecectomy caused significantly higher moisture content in excreta (P <0.01). 4. Gastrointestinal passage time of digesta was significantly shorter in caecectomised chicks than in control chicks (P <0.05). 5. Caecectomy tended to improve nitrogen utilisation rate in growing chicks. 6. The treatment significantly decreased uric acid excretion (P <0.01) and excretory uric acid-N/total nitrogen excretion (P <0.01). 7. It is concluded that the effects of caecectomy on nitrogen metabolism in growing chicks are similar to those in adult chickens.

Inhibitory effect of penicillin on caecal urease activity in chickens fed on a low protein diet plus urea

1. The effects of dietary penicillin on the urease activities of small intestine, large intestine, caecum and their contents, liver and kidney in chickens fed a diet containing 5 g/kg protein plus urea were examined. 2. About 0.88 of the total urease activity determined was observed in intestinal contents, of which 0.95 of the activity was accounted for by caecal contents, 0.05 by colo-rectal contents and none by small intestinal contents. Intestinal tissues (caecum included), liver and kidney accounted for 0.03, 0.06 and 0.02, respectively, of the total urease activity. 3. Dietary penicillin decreased urease activity to 0.17 in caecal contents and to 0.05 in colo-rectal contents of the corresponding control values (P < 0.01). The urease activity of caecal tissue was lowered by penicillin to half that of control activity (P < 0.05) but none of the activities of other tissues were affected. 4. It is concluded that, even when the urease activity is stimulated by dietary urea, 20 mg/kg dietary penicillin can strikingly lower it in the caecum, where most of the urease activity in the chicken body is to be found.

Ammonia production from amino acids and urea in the caecal contents of the chicken.

1. Ammonia production from urea and amino acids in the caecal contents of the chicken was evaluated using 15N-labeled nitrogenous compounds. 2. About 43% of each of urea nitrogen and glutamine amide nitrogen was converted to ammonia nitrogen, but only 25% of epsilon-nitrogen of the added arginine, a precursor of urea, was found in ammonia. 3. Amino nitrogen of the separately added glutamic acid and glycine to be converted to ammonia was 19-20% of their added amounts, whereas that of alpha-alanine was 11%. 4. It is concluded that dietary and urinary amino acids and urea which find their ways into the caeca are useful nitrogen sources for ammonia production by microflora in the caeca of the chicken.

Incorporation of intraportal ammonia-N into blood and tissue nitrogenous compounds in chickens fed low and high protein diets

1. 15N-Percentage of the amide of glutamine in total blood non-protein-15N was 42 and 48% in chickens fed 5 and 20% protein diets, respectively, when 15N-ammonia was intraportally-infused for 6 hr. 2. The infused ammonia-15N also appeared in the amide of free glutamine in the liver and kidney in large amounts at both levels of protein intake. 3. The 15N incorporated into glutamine-amide in the blood, liver and kidney and non-protein-15N in plasma were greater in chickens fed the low protein diet than in those fed the high protein diet (P less than 0.05 except kidney of P less than 0.01). 4. About 60% of the amide-N of the glutamine which was increased during 6 hr infusion of ammonia was derived from infused ammonia-N and the remainder from endogenous nitrogen, irrespective of protein intake. 5. These results suggest that glutamine is the most important intermediate in detoxication of intraportal ammonia in chickens.

Ligation of caeca improves nitrogen utilisation and decreases urinary uric acid excretion in chickens fed on a low protein diet plus urea

1. The effect of the ligation of the caeca on nitrogen utilisation and nitrogen excretion was examined in conventional chickens fed a diet containing 50 g protein/kg plus urea. 2. Ligation of the caeca significantly improved nitrogen balance and utilisation by up to more than 2 times as much as those of controls (P < 0.05). 3. The treatment significantly decreased uric acid excretion by 77 mg nitrogen/day (P < 0.01) and also total nitrogen excretion (P < 0.05): the former decrease almost explained the latter. 4. No effect of the ligation of caeca on urea and ammonia excretion was observed. 5. It is concluded that nitrogen metabolism in chickens is affected by possible changes in caecal fermentation by preventing entry into the caeca of substances from urine and digesta.

In situ degradation and absorption of [15N]urea in chicken ceca

[15N]Urea was introduced (in situ) into a ligated cecal pouch of chickens to determine if it is degraded therein and absorbed into the blood as ammonia during the following 60 min. A mean of 49% of the introduced urea-15N was recovered from the blood of the mesenteric vein draining the cecal pouch and 26% was recovered from the cecal lumen fluid. Of the urea-15N introduced into the pouch, 4%, 2%, 15% and 5% were detected as urea, ammonia and non-protein fractions, except urea and ammonia, and proteins in the lumen fluid, respectively. Non-protein-15N, except urea and ammonia, protein-15N, urea-15N and ammonia-15N values recovered in the cecal venous blood were 10%, 19%, 18% and 2% of the introduced 15N, respectively. Urea concentration in the cecal venous blood increased from 0.71 mg to 3.13 mg per 100 ml for the first 15 min after introduction of urea-15N (P < 0.01) then decreased until 60 min. No significant change was found in blood ammonia concentration, however, despite a small increase during the period 15-45 min after urea-15N introduction. Ammonia-15N increased in the caecal venous blood for the first 30 min then decreased to a plateau level of 43% of the peak level. The rates of increase of urea-15N and non-protein-15N concentrations attained maxima in the blood as early as 15 min, then decreased linearly (P < 0.05). It is concluded that, although urea is actively degraded to ammonia in the ceca, it is mostly absorbed from the ceca, not in the form of ammonia, but as protein, urea and amino acids.

Effect of dietary protein and urea on in vitro caecal ammonia production from urea and uric acid in cockerels.

1. Single Comb White Leghorn adult cockerels were fed on 50 g/kg protein diet, 200 g/kg protein diet or 50 g/kg protein diet plus urea and in vitro ammoniagenesis from urea and uric acid in the caeca was determined. 2. Four-fold protein intake caused about 4.6-fold increase in caecal ammonia production from urea (P < 0.05), and tended to increase it from uric acid as compared with 50 g/kg protein-fed birds. 3. Dietary urea significantly increased caecal ammonia production from urea and uric acid by about 2 and 3 times as much as those of control birds, respectively (P < 0.05). 4. It is concluded that increased protein intake and the feeding of urea are able to induce ammoniagenesis from urea and uric acid in the caeca of fowls.

Relationship of decreased caecal urease activity by dietary penicillin to nitrogen utilisation in chickens fed on a low protein diet plus urea

1. The relationship of the decreased caecal urease activity by dietary penicillin to nitrogen utilisation was assessed in chickens fed a low protein diet plus urea. 2. Dietary penicillin at 20 and 100 mg/kg decreased anaerobic bacteria counts, urease activity and ammonia concentration in caecal contents (P < 0.05, except for ammonia in the case of the 100 mg/kg penicillin diet). 3. The 20 mg/kg penicillin diets significantly increased the excretion of urea and total nitrogen (P < 0.05) and decreased ammonia excretion, and significantly reduced nitrogen retention (P < 0.05). The 100 mg/kg penicillin diet also resulted in similar but not significant changes, which tended to be less than those by the 20 mg/kg penicillin diet. 4. Ammonia, urea, glutamine and uric acid concentrations in blood, liver and kidney were unchanged by dietary penicillin. 5. It is concluded that caecal ammonia production from urea was closely correlated with nitrogen utilisation in chickens fed a low protein diet plus urea.