The role of the gut microflora in the utilization of dietary urea by the chick

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Abstract
In a preliminary experiment, growth of conventional chicks given a basal diet containing adequate amounts of all the essential but none of the non-essential amino acids was improved by supplements of 10.3 g urea or 50.4 g glutamic acid/kg diet or both. In the main study the effects of supplementing the basal diet with 20.6 g urea/kg were compared in groups of 16 germ-free and conventional chicks. The germ-free chicks did not benefit from the urea supplement. The conventional birds showed improved food conversion efficiency and significantly better growth. In both experiments N retention ((mg N intake-mg N excreted) .div. g food intake) was higher in the birds given urea, but N utilization ((mg N intake-mg N excreted) .div. mg N intake) was reduced. This reduction was greater in the germ-free birds. There was a small increase in plasma ammonia concentration in the germ-free birds given urea but a significantly greater increase in the corresponding conventional group. Plasma uric acid concentrations were variable in both groups and much lower than the normal range. They followed a similar pattern to the plasma ammonia values. More insoluble N was excreted by the conventional chicks given urea than by the corresponding germ-free group or by either group given the basal diet. The gut micro-organisms are apparently responsible for the growth-promoting effect of urea, presumably through release of ammonia by bacterial urease (EC 3.5.1.5) and its consequent incorporation into amino acids.