RELATIONSHIPS AMONG SPLANCHNIC TISSUE ENERGY-CONSUMPTION AND NET FLUXOF NUTRIENTS, FEED-INTAKE AND DIGESTIBILITY IN WETHERS CONSUMING FORAGE-BASED DIETS AD-LIBITUM

Data from crossbred catheterized wethers (38+/-0.6 hg body weight) con suming forage-based diets ad libitum in eleven experiments were used t o determine relationships among splanchnic tissue energy consumption a nd net flux of nutrients, feed intake and digestibility. Portal-draine d viscera (PDV) and hepatic energy consumption increased lineally as d igestible energy intake (DEI) increased (PDV energy consumption, Mcal/ d = 0.2005 + 0.0660 [DEI; Mcal/d] R(2) = 22%; hepatic energy consumpti on, Mcal/d 0.1457 + 0.0659 [DEI, Mcal/d R(2) = 25%. However; improveme nts in R(2) occurred when other independent variables were included in regressions (PDV energy consumption, Mcal/d = -0.0112 + 0.1659 [DEI; Mcal/d] - 0.0254 [DEI(2), Mcal/d] + [fecal neutral detergent fiber, kg /d] R(2) 34%; hepatic energy consumption = 0.0014 + 0.0266 [DEI, Mcal/ d] + 0.3325 [PDV energy consumption, Mcal/d] + 0.0745 [hepatic urea ni trogen net flux, M/d] + 0.0016 [body weight, kg] R(2) = 48%). Splanchn ic bed energy consumption as a percentage of DEI was best described (R (2) = 49%] by, 43.611 - 9.531 [DEI, Mcal/d] + 15.914 [fecal neutral de tergent fiber; kg/d] + 6.057 [hepatic urea nitrogen net flux, M/d]. A regression of hepatic urea nitrogen net flux on hepatic net fluxes of alpha-amino and ammonia nitrogen accounted for 25% of valuation, of wh ich 55 and 45% was attributable to alpha-amino and ammonia nitrogen, r espectively. In conclusion, factors besides physiological workload as depicted by DEI accounted for variability in energy consumed by splanc hnic tissues with ad libitum ingestion, of forage-based diets. The dec reasing operation of DEI attributable to splanchnic bed use may, contr ibute to change in animal performance with increasing DEI.