Hepatic Urea Synthesis and Site and Rate of Urea Removal From Blood of Beef Steers Fed Alfalfa Hay or a High Concentrate Diet

Huntington, G. B.

doi:10.4141/cjas89-025

Cited by 132 publications

(134 citation statements)

References 18 publications

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“…One factor is dietary N intake affecting plasma urea concentration that again influences the urea content of saliva (Bailey and Balch, 1961). However, at low N intakes where the plasma concentration of urea is low, the bulk of the recycled urea is transported directly from blood across gastro-intestinal epithelia (Huntington, 1989). This is in agreement with data from the present study showing that dairy cows fed a diet severely deficient in rumen degradable protein transferred 86% of the total recycled urea by direct transfer across epithelial membranes and only 14% of the total recycled urea via saliva.…”

Section: Hoursupporting

confidence: 92%

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Røjen

Lund

Kristensen

2008

Animal

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Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 6 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portaldrained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.

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Section: Hoursupporting

confidence: 92%

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Røjen

Lund

Kristensen

2008

Animal

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“…Contradictory results were found in the literature (Reynolds & Huntington, 1988a;Huntington, 1989;. With forage diets, peristalsis and, hence, smooth muscle contraction work is enhanced by bulk, which could have increased blood flows through the muscular tissues of the gut.…”

Section: Nutrient Supply and Net Fluxes Through Portal-drained Viscerasupporting

confidence: 70%

Whole-body fuel selection in ruminants: nutrient supply and utilization by major tissues

Ortigues

Visseiche

1995

Proc. Nutr. Soc.

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“…Ainda houve interação (P<0,02) nível de volumoso × fonte de carboidrato para o fluxo portal de amônia. Huntington (1989) comparou duas dietas, uma à base de feno de alfafa (162 g de N/dia) e a outra com 75% de concentrado, composta basicamente por milho (95 g de N/dia), em novilhos com ingestões similares de EM. A concentração portal de amônia foi diferente entre dietas compostas basicamente por feno de alfafa e por concentrado, com médias de 0,752 e 0,554 mM, respectivamente.…”

Section: Resultsunclassified

Fontes de carboidratos e porcentagem de volumosos em dietas para ovinos: balanço de nitrogênio, digestibilidade e fluxo portal de nutrientes

Mouro

Branco²,

Harmon

et al. 2007

R. Bras. Zootec.

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Avaliou-se a influência de duas fontes de carboidrato (casca de soja e milho em grão) e de dois níveis (40 e 70%) de volumoso nas dietas sobre a digestibilidade dos nutrientes, o balanço de nitrogênio e o fluxo portal de nutrientes em ovinos. Foram utilizados quatro ovinos Corriedale (45 kg PV) com três cateteres implantados (veia e artéria mesentérica e veia porta), distribuídos em delineamento quadrado latino. A digestibilidade dos nutrientes foi obtida utilizando-se a técnica de coleta total de fezes e urina e o fluxo portal de nutrientes pelo princípio de Fick. A digestibilidade da MS das dietas contendo milho (66,7%) foi maior que daquelas contendo casca de soja (60,9%). A ingestão (789,7 g/dia), a digestão (444,2 g/dia) e a digestibilidade (56,2%) da FDN foram maiores para as dietas contendo casca de soja como fonte de carboidrato. As dietas contendo milho proporcionaram maior ingestão e digestão do EE. Houve efeito da interação fonte de carboidrato <FONT FACE=Symbol>´</FONT> proporção de volumoso sobre a ingestão e a digestão dos CNF. Os valores de ingestão e digestão nas dietas com milho foram maiores na menor proporção de volumoso, mas, naquelas com casca de soja, não foram influenciados pelas proporções de volumoso estudadas. O teor de NDT foi maior para as dietas contendo milho. Dietas com 40% de volumoso resultaram em menores perdas fecais e urinárias e em maiores digestibilidade e retenção de nitrogênio. As concentrações portal e arterial de glicose foram maiores para dietas contendo milho e para aquelas contendo 40% de volumoso. As concentrações portal de amônia e uréia, assim como a diferença venosa-arterial e o fluxo portal de amônia, foram menores para dietas com 40% de volumoso.

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Hepatic Urea Synthesis and Site and Rate of Urea Removal From Blood of Beef Steers Fed Alfalfa Hay or a High Concentrate Diet

Abstract: Daily grab samples of feed were composited weekly, then ground (l mm). Dry matter was determined gravimetrically (24 h, 100'C), and N content of samples was determined using Kjeldahl procedures. Steers were weighed biweekly.

Cited by 132 publications

References 18 publications

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Whole-body fuel selection in ruminants: nutrient supply and utilization by major tissues

Fontes de carboidratos e porcentagem de volumosos em dietas para ovinos: balanço de nitrogênio, digestibilidade e fluxo portal de nutrientes

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