[Nitrogen metabolism in the broiler chicken determined by means of 15N labeled wheat]

Endogenous N-losses in broilers estimated by a [15N]-isotope dilution technique: effect of dietary fat type and xylanase addition

Male broilers were given a low protein diet (15.5% CP) spiked with [15N]H4HCO3 from day 12 to day 18 of age to label the endogenous N-constituents. Experimental diets were subsequently fed from day 19 to day 24 of age and consisted of a rye based diet (56% dietary inclusion) which contained either 10% soya oil (S) or 10% beef tallow (T), each of which was either unsupplemented (-) or supplemented (+) with a xylanase containing enzyme preparation (2700 IU/kg at pH 5.3). [15N]-atom percent excess (APE) of excreta, faeces and urine were monitored on a daily basis during both experimental periods. Furthermore, APE was measured in various tissues at the end of the experiment. The APE of urine on the last day of the experiment was between the APE of the pancreas and that of the jejunal tissue, an observation which supported the usefulness of using urinary APE as an indicator for the endogenous N-pool. Endogenous N-proportions were estimated by an isotope dilution technique at the end of the experiment by examination of the ratio of APE in faeces and urine. The endogenous N-proportion in the faeces was greatest in birds receiving the T(-) diet. The proportions were 0.321, 0.319, 0.451 and 0.289 in S(-), S(+), T(-) and T(+) fed groups, respectively. Xylanase addition reduced endogenous N-proportion, a factor which was used to correct apparent crude protein digestibility (85.6, 86.2, 84.3 and 88.5% in S(-), S(+), T(-) and T(+) fed birds, respectively) for endogenous losses resulting in almost equal true digestibilities of crude protein for all treatments (90.3, 90.6, 90.4 and 91.5%). The amounts of endogenous N in faces were estimated to be 87, 69, 244 and 81 mg per day per kg0.67 body weight in S(-), S(+), T(-) and T(+) fed birds, respectively. It was concluded that xylanase supplementation of a rye based broiler diet does not change endogenous N-secretions when the supplemental fat is soya oil. However, addition of tallow rather than soya oil increased these N-losses significantly, an effect which was reversed by xylanase addition.

[Nitrogen metabolism of broilers fed 15-N labeled wheat. 4. 15-N concentration in muscles and nitrogen utilization]

Broilers were fed 15N labelled wheat and the concentration of the labelled isotope in muscular tissue was determined. A negative correlation was found to exist between the percentage proportion of N in the muscle fractions and the level of 15N frequency established 12 hrs after administration of the labelled ration. Higher rates of tracer incorporation were observed in the muscles of legs and other muscles (predominatly red muscles) than in pectoral muscles (white muscles). The heart was shown to exhibit the lowest N content and the highest level of 15N frequency of all muscle fractions. In view of the fact that some specific difficulties will arise when certain factors (trace elements, vitamins, ergotropic substances, genetic factors) which influence the N metabolism of fattening poultry, are estimated on the basis of the conventional N balance trials the present tracer technique is recommended for use as an alternative method in studies of the kind just described. In the present trial 20% of the wheat N were utilized for the production of meat N in muscular tissue.

[Nitrogen metabolism of broilers fed N-15 labeled wheat. 3. Blood, liver, spleen, thymus, kidney, brain, pancreas, labile N reservoir]

Studies on the N metabolism of 4-week-old male broilers fed 15N Labelled wheat revealed a close correlation existing between the levels of 15N concentrations in the small intestine and in the plasma NPN fraction of the blood. The highest level of excess 15Natom0/0 in plasma proteins was noted as late as 20-30 hrs after administration of the last tracer dose. The mean life time of plasma proteins in broilers is less than 2.0 days. The rapid and statistically significant decrease of 15N frequency in the liver, spleen, thymus, and kidneys in the period from 12 hrs after withdrawal of the last 15N dose until the end of the trial reflects the intensity of N turnover in these organs. In the period from 6 hrs to 12 hrs after the last N intake the mean quantities of N in the liver, small intestine and kidneys decreased by 18%, 29%, 26% and 16%. The quantity of N accumulated in these organs after food intake is gradually released into the organism.

[The nitrogen metabolism of broiler chickens with 15N-labeled wheat. 2. Report. 15N concentration in the gastrointestinal tract and its contents]

17 broilers received a wheat-soya bean meal-pea nut ration containing an excess of 15N atom% (6.54%). The birds were slaughtered 3, 6, 12, 36, 60 and 108 hours after the last 15N'-intake. Up to 12 hrs after slaughtering the contents of the crop and the stomachs were found to contain a higher excess of 15N atom% than the food. The contents of the small intestine at that time contained only 1/4 of the 15N concentration present in the crop and the stomachs (2.7%). Later on the excess of 15N atom% decreased to 1.7%, 1.4% and 0.8% and was 4 times as high as that found in the crop and the stomach. Higher 15N' concentrations, compared with those in the small intestine, were found in the contents of the caecum, the colon, and the rectum, for a period of up to 12 hrs after administration of the last portion of labelled food. The 15N' concentrations in the crop and the stomachs are due to a more prolonged storage of wheat relative to that of the extracted meals. The interrelationship between the contents of the small intestine and the contents of the higher sections of the gastro-intestinal tract suggests that a secretion of N-containing substances takes place, although it was not possible to determine these substances quantitatively. Values for the excess of 15N atom% in the crop and oesophagus and in the muscular stomach were found to be in close correspondence both with regard to their level and time pattern. The decline in the glandular stomach was more rapid than in the muscular stomach. A very close correlation (r=0.99) was found between the 15N atom% in the contents of the intestine and in the intestinal wall. The N content of the small intestine (expressed as mg) was significantly higher after 3 hrs and 6 hrs of fasting than after a fasting period of 12 hours. Theoretical aspects of the involvement of the intestine in the process of metabolism are discussed in some detail.