Transfer of urea from the blood to the rumen of sheep

Kennedy, P. M.; Milligan, L. P.

doi:10.1079/bjn19780105

Cited by 65 publications

(21 citation statements)

References 13 publications

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“…There are many ways in which the total urea movement and the distribution of movement of urea to various sectors of the gut can vary. Relative permeability of the rumen wall has been suggested to vary (Engelhardt et al 1978), and it has been suggested that the entry of urea into the reticulorumen is enhanced when ruminal ammonia concentration is low (Houpt, 1970;Kennedy & Milligan, 1978). whereby virtually total reabsorption of plasma urea-derived NH, (carrying 15N label, if present) can occur, but the efficiency of use of 'deep digesta' NH, may be improved.…”

Section: Nitrogen Metabolism 81mentioning

confidence: 99%

“…Intake and net gain in nitrogen (as non-ammonia-N) Kennedy & Milligan, 1978). However, the nature of the processes involved allows for significant departures from the ideal conditions of mixing (assumed to operate in isotope studies) and thus leads to uncertainty about the direct and indirect influences, particularly of the blood urea-N contribution, to rumen N metabolism.…”

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confidence: 99%

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Host Animal—rumen Relationships

Egan

1980

Proc. Nutr. Soc.

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Section: Nitrogen Metabolism 81mentioning

confidence: 99%

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confidence: 99%

Host Animal—rumen Relationships

Egan

1980

Proc. Nutr. Soc.

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“…N transfer between the rumen NH,-N and blood urea-N pools were calculated using a two-pool model (Nolan et al 1976;Kennedy & Milligan 1978~). Transfer quotients were calculated from the enrichment ratio with 15N of the two pools of interest.…”

Section: N Calculationsmentioning

confidence: 99%

Kinetics of nitrogen transfer across the rumen wall of sheep given a low-protein roughage

Neutze

Kellaway²,

Faichney³

1986

Br J Nutr

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1, The significance of blood urea-nitrogen transfer to the rumen was examined in sheep given alkali-treated wheat straw supplemented with 3.5 (diet A), 5.9 (diet B) and 11.6 (diet C) g urea-N/kg dry matter (DM).2. Mean voluntary intakes of DM (g/d) were 897, 1149 and 1225 for diets A, B and C respectively, indicating significant (P < 0.05) intake responses to urea supplementation. Digestion studies were conducted at 90% of voluntary intake. Dietary N intakes (g/d) were 7.1, 11.5 and 18.6 for diets A, B and C respectively. 3. Absorption of ammonia-N from the rumen (g/d) was 3.5, 6.7 and 8.9 for diets A, B and C respectively, with all dietary differences being significantly different (P < 0.05). 4.Non-ammonia-N (NAN) leaving the abomasum (g/d) was 9.6, 12.7 and 14.8 for diets A, B and C respectively. Microbial N leaving the abomdsum (g/d) was 6.8, 9.6 and 10.7 for diets A, B and C respectively.Hence, significantly (P < 0.05) more N was provided to the intestines with increased urea supplementation. Net efficiencies of microbial protein synthesis (g N/kg organic matter apparently digested in the rumen), estimated from 16N incorporation, were 24.2, 23.7 and 25.3 for diets A, B and C respectively, and were not significantly different (P > 0.05). . ~~~~ B and C respectively, reflecting the high proportion of total N as urea-N in the diets. Proportions of microbial N derived from blood urea-N were 0.31, 0.21 and 0.12 for diets A, B and C respectively, indicating a decreasing significance of blood urea as a source of microbial N as dietary urea increased ( P < 0.05). 6. Transfer of blood urea-N to the rumen (g/d) was 3.8, 4.7 and 2.6 for diets A, B and C respectively, being significantly (P < 0.05) lower on diet C. Using an estimate ,of the salivary contribution of urea-N to the rumen, it was concluded that there was a significant though not large transfer of blood urea-N across the rumen wall on all diets. 7. Net transfer of blood urea-N to the rumen was estimated from a two-pool model and was +0.4 g/d for diet A, though this was not significantly different from zero. Net transfers for diets B and C were -2.0 and -6.3 g N/d respectively.8. Significant intake responses to exogenous urea supplementation were observed because of a limited capacity to recycle N to the rumen under the conditions of low dietary N supply imposed.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Whitelaw¹,

Milne²,

Er³

et al. 1990

Experimental Physiology

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SUMMARYA comparison has been made of the kinetics of urea metabolism in sheep given conventional feeds or maintained wholly by intragastric infusions of volatile fatty acids, buffer, mineral and casein solutions. Daily nitrogen supply was 132 g/day in 'fed' sheep and 6-0 g/day in 'infusion' sheep. On each feeding system measurements were made at the basal (maintenance) level of intake and when the basal level was supplemented with infusions of urea into the abomasum (125 mmol/day) or into the rumen (300 mmol/day). Additional measurements were made when ammonium carbonate (100 mmol/day) was infused into the rumen, when cassava (150 g/day) was added to the diet of 'fed' sheep or when the input of casein to 'infusion' sheep was reduced by half. Urea kinetics were measured by means of a single intravenous injection of ['4C]urea. Urea irreversible loss rate, urea pool size, urinary urea excretion, plasma urea concentrations and rumen ammonia concentrations were all significantly higher in sheep given conventional feeds than in those nourished by infusion but urea degradation in the gastrointestinal tract did not differ between the two methods of feeding. Regression analysis indicated only minor differences between the two feeding systems in the relationships between the various indices of urea metabolism. It is concluded that most of these findings can be attributed to differences in the quantity and nature of the nitrogen supplied in the basal diets and that the sheep nourished by infusion would be a suitable model for the study of factors involved in the control of urea recycling.

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Transfer of urea from the blood to the rumen of sheep

Cited by 65 publications

References 13 publications

Host Animal—rumen Relationships

Host Animal—rumen Relationships

Kinetics of nitrogen transfer across the rumen wall of sheep given a low-protein roughage

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

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