Abstract
Four calves equipped with permanent rumen and T-piece duodenal caninulus were given four diets in a Latin square experiment carried out at two stages of development. DM flow was measured by dual-phase markers. The basal diet of hay and concentrate was calculated to be low In rumen degradable N (RDN) and. tissue N. Additional RDN was provided by adding 6, 12 or 18g urea/kg concentrate. Supplementary urea did not affect OM digestion either in the stomach or In the entire digestive tract. At the older age OM digestion in the stomach and the entire tract was significantly higher. On the basal diet, N retention was low. The flow of microbial N measured by the DAPA technique was not affected by diet and it was calculated that between 3 and 7g "s/d were recycled to the rumen. The addition of supplementary urea increased N retention particularly at the lowest level of supplementation due to a concomitant decrease In urinary N.
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