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Le recyclage de l'azote dans le tractus gastro-intestinal
Orskov E.R., Whitelaw F.G.
in
Tisserand J.-L. (ed.).
Séminaire sur la digestion, la nutrition et l'alimentation du dromadaire
Zaragoza : CIHEAM
Options Méditerranéennes : Série A. Séminaires Méditerranéens; n. 2
1989
pages 99
Article available on lin e / Article dispon ible en lign e à l’adresse :
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-------------------------------------------------------------------------------------------------------------------------------------------------------------------------To cite th is article / Pou r citer cet article
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------Orskov E.R., Whitelaw F.G. Le recyclage de l' azote dan s le tractu s gastro-in testin al. In : Tisserand
J.-L. (ed.). Séminaire sur la digestion, la nutrition et l'alimentation du dromadaire. Zaragoza : CIHEAM,
1989. p. 99 (Options Méditerranéennes : Série A. Séminaires Méditerranéens; n. 2)
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CIHEAM - Options Mediterraneennes
de l'azote
E. R. ORSKOV
F.
WHITELAW
ROWET RESEARCH INSTITUTE
ABERDEEN (ENGLAND)
- cditrogen re-cycling to the gastro-intestinal tractb.
The ability
from the blood to the gastrointestinal tract can be major nutritional significance under arid and semi-arid conditions wherethe available food supply frequently
consist ofpoor-qualityforages, low in availableh? Under these conditions the
transfer urea to therumen allows normal microbial activity
in feed intake which would
and rumenfunction to be maintained andso delays for a time the depression in organic matter digestibility and
otherwise ensue.Although urea recycling can account for over 90% urea synthesis rate when dietary protein supply is deficient, it is
important to recognize that
loss
from the body still occurs and the process will eventually
wind-dowm if undernutrition is prolonged,
At the other extreme urea recyclingas high as 50%
it
is not known whether this confers any nutritional advantage tothe host. Although many theories have been advanced over thepast thirv
years, the spec@ mechanisms involved in the control urea transfer to thegut have notyet been completely resolved,
One obvious route urea recycling via saliva and urea Concentrations in saliva are known to be highly correlated with concentrations
in plasma This
situation however, suggests
that the quantities transferredmay well be minimal when the microbial needs
for N are greatest.
is regulated
The alternative route bypassage across therumen wall andhere opinionsdiffer to whether it a purely passive process or
by factors such as ammonia concentration gradient,effects of ammonia on bacterial urease activities or changes
in the permeability the
rumen epithelium, mediated by local concentrations fermentation end
is accumulating also that considerable movement urea cai occur across thepost-rumen digestive tract and that the control urea transfer at these sites probably differentfrom
that in the rumen.
an attempt to resolve some these problems, comparisons have been made between
ruminants nourished by normalfeeds and those
sustained wholly by intragastric infusions all nutrients. These experiments have shown that fermentation in the rumen not a prerequisite for normal urea recycling since the quuwtities trmferred to the gastro-intestinal tract were similar in the two situations.
subsequent trials, the establishement microbial fermentations in either thefore-stomach or the hind-gut animals otherwise nourished
solely byinjiuion had no effect on the total quantity urea recycled to the gut.
The possible contribution recycled urea to.the nitrogen economy the ruminant in adverse dietary situations will be discussed
words: Dromedary,
-
à
de
à
d'une
à la quantité
à une activité
où la
de
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continue à
ne
peut
que 50%de celui de
de 90%
en cas
des
que beaucoup de
synthèse, il
A
d'azote, mais on ne
sait pas si
un
ces 30
le
mécanisme spécifique
n'a jamais été complètementélucidé.
La salive constitue une voie évidentede
de
les
la
à celles du
élevés.
passage à
mais ici les
quant à
s'ils'agit d'un simple phénomène passif ou
on
de
effects
l'activité des
ou des
l'épithélium
de
des
l'existence d'un
à
le
digestif
de celui
Afin de
voie
de tous les éléments
n'est
de
l'intestin d'un
On discute ausside la
Options
n'a pas
l'intestin.
de
-
des
- n.O 2 -
1989: 99
Serie A: Seminaires mediterraneens