{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,19]],"date-time":"2026-02-19T16:57:57Z","timestamp":1771520277837,"version":"3.50.1"},"reference-count":37,"publisher":"Cambridge University Press (CUP)","issue":"1","license":[{"start":{"date-parts":[[2008,3,25]],"date-time":"2008-03-25T00:00:00Z","timestamp":1206403200000},"content-version":"unspecified","delay-in-days":11772,"URL":"https:\/\/www.cambridge.org\/core\/terms"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Br J Nutr"],"published-print":{"date-parts":[[1976,1]]},"abstract":"<jats:p>1. A study of ammonia and urea metabolism in sheep was made using isotope dilution techniques with (<jats:sup>15<\/jats:sup>NH<jats:sub>4<\/jats:sub>)<jats:sub>2<\/jats:sub>SO<jats:sub>4<\/jats:sub>, [<jats:sup>15<\/jats:sup>N]urea and [<jats:sup>14<\/jats:sup>C]urea in order to determine quantitatively the movements of urea-N and NH<jats:sub>3<\/jats:sub>-N throughout the body of normal, feeding sheep.<\/jats:p><jats:p>2. Single injections of<jats:sup>15<\/jats:sup>N-labelled compounds were made into the rumen fluid NH<jats:sub>3<\/jats:sub>, caecal fluid NH<jats:sub>3<\/jats:sub>and the blood urea pools, in order to estimate the rates of flux through, and the transfer of N between, these and other nitrogenous pools in the body.<jats:sup>51<\/jats:sup>Cr EDTA was injected into the rumen and caecum with (<jats:sup>15<\/jats:sup>NH<jats:sub>4<\/jats:sub>)<jats:sub>2<\/jats:sub>SO<jats:sub>4<\/jats:sub>to allow estimation of fluid volumes and to provide an indication of mixing, and of times of transit of isotopes between different sampling sites in the digestive tract.<\/jats:p><jats:p>3. The sheep ate approximately 22 g lucerne chaff\/h and the mean dietary N intake was 16.3 g\/d.<\/jats:p><jats:p>4. The rate of flux of NH<jats:sub>3<\/jats:sub>through the rumen NH<jats:sub>3<\/jats:sub>pool was 15.0 g\/d (i.e. 90% of the dietary N ingested; however, this amount also included N from plasma urea (1.1 g\/d) and other endogenous sources including NH<jats:sub>3<\/jats:sub>derived from caecal NH<jats:sub>3<\/jats:sub>(0.4 g\/d).<\/jats:p><jats:p>5. Only 40% of the N in isolated rumen bacteria was derived from NH<jats:sub>3<\/jats:sub>, indicating that a considerable proportion of their N requirements were obtained from compounds other than NH<jats:sub>3<\/jats:sub>(e.g. peptides and amino acids).<\/jats:p><jats:p>6. There was evidence of recycling of N between nitrogenous pools in the rumen, probably through rumen NH<jats:sub>3<\/jats:sub>\u2192 microbial N \u2192 NH<jats:sub>3<\/jats:sub>.<\/jats:p><jats:p>7. It was estimated that 5.3 g blood urea-N\/d entered the digestive tract: 20% of this urea was degraded in the rumen, 25% in the caecum and the remainder was apparently degraded elsewhere; there was evidence of urea degradation in the large intestine posterior to the caecum and it is suggested that urea degradation and absorption of the resultant NH<jats:sub>3<\/jats:sub>may occur in the ileum.<\/jats:p><jats:p>8. Of the 4.8 g N\/d entering the caecal NH<jats:sub>3<\/jats:sub>pool, 4.2 g N\/d left and did not return and the difference (0.6 g N\/d) was recycled, possibly through caecal NH<jats:sub>3<\/jats:sub>\u2192 microbial N \u2192 NH<jats:sub>3<\/jats:sub>.<\/jats:p><jats:p>9. A large proportion of the NH<jats:sub>3<\/jats:sub>entering the caecal NH<jats:sub>3<\/jats:sub>pool (70% or 3.2 g N\/d) was apparently derived from degradation of nitrogenous products, other than urea, including rumen microbial N (1.0 g N\/d) passing undigested from the small intestine.<\/jats:p><jats:p>10. Less than half the NH<jats:sub>3<\/jats:sub>-N of caecal origin entering the rumen passed through the blood urea pool; the remainder was apparently transported as other nitrogenous compounds in the blood or body fluids.<\/jats:p><jats:p>11. The results of the three experiments were combined in a general three-pool, opencompartment model which formally recognizes an unlimited number of other unspecified, interconnected pools together comprising the whole-animal system. Rates of flux through, and transfer of N between these and other nitrogenous pools in the body were calculated by solving this model and the information derived has been applied to whole-animal models with a view to subsequently using these models in computer simulation studies.<\/jats:p>","DOI":"10.1079\/bjn19760016","type":"journal-article","created":{"date-parts":[[2005,5,19]],"date-time":"2005-05-19T23:49:52Z","timestamp":1116546592000},"page":"127-147","source":"Crossref","is-referenced-by-count":103,"title":["Further studies of the dynamics of nitrogen metabolism in sheep"],"prefix":"10.1017","volume":"35","author":[{"given":"J. V.","family":"Nolan","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"B. W.","family":"Norton","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"R. A.","family":"Leng","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"56","published-online":{"date-parts":[[2008,3,25]]},"reference":[{"key":"S0007114576000822_ref010","first-page":"231","volume":"62","author":"Giordano","year":"1963","journal-title":"J. Lab. clin. Med."},{"key":"S0007114576000822_ref036","doi-asserted-by":"publisher","DOI":"10.1042\/bj1140203"},{"key":"S0007114576000822_ref035","doi-asserted-by":"publisher","DOI":"10.1172\/JCI103940"},{"key":"S0007114576000822_ref034","doi-asserted-by":"publisher","DOI":"10.2527\/jas1968.2761703x"},{"key":"S0007114576000822_ref025","unstructured":"Murray R. M. (1973). Nutrition and digestive function of the ruminant. 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