In order to measure the net portal and visceral flux of metabolites in lambs (35 ± 2.5 kg live weight) fed rice-grass (Echinochloa sp.) hay cut at 32, 46, 72 or 96 days of regrowth age, two assays were carried out. One of them was a 4 × 4 Latin Square experiment (Assay 1) where the four hays were evaluated and the other was a 3 × 3 Latin square experiment (Assay 2) that did not include the 32-day hay. Animals were surgically implanted with permanent catheters into mesenteric and hepatic blood vessels. Arterial blood was sampled using temporary catheters into carotid artery. Portal and visceral blood flow was estimated based on continuous infusion of paraminohippurate in a mesenteric vein. On the sampling day, total and digestible organic matter (OM) intakes were not affected, but total and digestible N intakes decreased linearly with the increased forage regrowth age in both assays. The portal and visceral blood flow, net visceral flux of glucose, urea and amino acids and the net portal flux of glucose and urea were not affected by forage regrowth age. The net portal flux of amino acids and ammonia which was markedly higher in lambs fed 46-day hay and that ingested more digestible N. Most nutrients absorbed by lambs fed rice-grass hay were metabolized by visceral tissues such as peripheral availability of amino acids and glucose only account to a small proportion of N and OM intake. In general, the visceral metabolism of lambs is not clearly affected by forage regrowth age.
amino acids; ammonia; Echinochloa sp.; glucose; metabolism; urea
