Nitrogen metabolism in the ovine stomach: 1. The transfer of urea from the blood to the rumen

Abstract

The effect of single, intravenous injections of urea on the concentration of ammonia in the rumen has been examined in conscious and anaesthetized sheep.In conscious sheep maintained on a diet providing 11-4 g nitrogen/day, the net increase in concentration of rumen ammonia after the injection of urea showed negative correlations with the pre-injection concentrations of rumen ammonia and of plasma urea. The maximum concentration of ammonia attained in the rumen after the injection was 16-6 ± 0-28 mg NH 3 -N/100 ml. No such correlations were found in conscious sheep given a diet providing 20-7gN/day. In addition, the maximum concentration of ammonia attained in the rumen after the injection of urea was significantly lower at 10-7 + 0-91 mg NH3-N/IOO ml, and the net increases in concentration were smaller.Starvation for one day reduced the net increment in rumen ammonia concentration after urea injection in animals given the lower-N diet, to the same low level observed in fed or starved sheep maintained on the higher-N diet.Differences were observed in the transfer of blood urea to the rumen in experiments with anaesthetized sheep which had been maintained on the lower-N diet for long or short periods beforehand. Animals which had been left to graze, and then housed indoors and given the lower-N diet for a short period before the experiment, showed much smaller increases in rumen urea plus ammonia concentration after the injection of urea than sheep which had been given the same diet for a long period. There was no difference in the response of the salivary secretions to the urea injections.

Urea metabolism in sheep given conventional feeds or nourished by intragastric infusion

“…Although there is evidence that rumen NH3 concentration is an important factor in the regulation of urea entry into the rumen under practical feeding conditions (Varady, Boda, Bajo, Szanyiova & Tomas, 1973;Faichney, 1974;Harrop & Phillipson, 1974;Kennedy & Milligan, 1978, urea degradation has been shown to be influenced also by the addition of fermentable carbohydrate to the diet (Cocimano & Leng, 1967;Potthast, Rahman & Pfeffer, 1976;Engelhardt, Hinderer & Wipper, 1978;Kennedy, 1980), by perfusion of the digesta with CO2 (Thorlacious, Dobson & Sellars, 1971) or by increases in rumen butyric acid concentration (Hinderer & Engelhardt, 1976;Norton, Janes & Armstrong, 1982). Evidence is also accumulating that considerable movement of urea can 6&cur across the post-rumen digestive tract, particularly the small intestine (Varady, T4shenov, Boda, Fejes & Kosta, 1979;Egan et al 1986), and that the control of urea transfer at these sites is probably different from that in the rumen.…”

Nitrogen metabolism in the ovine stomach: 4. Nitrogenous components of the abomasal secretions

“…^e a n^m a^s w e r e maintained on a diet of chaffed meadow hay and flaked maize (CH + FM The abomasal secretions constitute a potentially diet). The diets and feeding times have been important, but hitherto neglected, pathway for the described elsewhere (Harrop & Phillipson, 1974a). recycling of nitrogen to the ruminant stomach.…”

Nitrogen metabolism in the ovine stomach: 2. Factors influencing ruminal ammonia levels in sheep maintained on different diets

“…In an earlier study, Harrop & Phillipson (1974) found that the intravenous injection of a standard quantity of urea produced mean maximum levels of 16-6 ±0-28 and 10-7 ± 0-91 mg ammonia-N/ 100 ml rumen liquor 4 h after injection, in sheep given the CH + FM and GGP diets respectively. In the experiments now described, the mean ruminal fluid volume of sheep given the CH + FM diet was only 78 % of that in GGP fed sheep.…”

“…of dilution or extent of utilization by microorganisms. In the preceding paper (Harrop & Phillipson, 1974), an upper limit was shown to exist for the EXPERIMENTAL PROCEDURE increase in concentration of rumen ammonia alter the intravenous injection of urea, in sheep given a Fourteen Clun Forest wethers of 1-3 years of age diet of chaffed meadow hay and supplements. This were used.…”

“…No such relationship was fitted with a rumen cannula. found among sheep given a higher nitrogen diet of A description of the diets provided, and feeding ground grass pellets, and differences between diets times, is given in the preceding paper (Harrop & could not be entirely accounted for by differences Phillipson, 1974). in prevailing concentrations of blood urea or rumen Samples of rumen contents were drawn under ammonia.…”