Relationships Among Splanchnic Tissue Energy Consumption and Net Flux of Nutrients, Feed Intake and Digestibility in Wethers Consuming Forage-Based Dietsad libitum

Goetsch, A.L. and Patil, A.R. 1997. Relationships among splanchnic tissue energy consumption and net flux of nutrients, feed intake and digestibility in wethers consuming forage-based diets ad libitum. J. Appl. Anim. Res., 11: 1–18. Data from crossbred catheterized wethers (38±0.6 kg body weight) consuming forage-based diets ad libitum in eleven experiments were used to determine relationships among splanchnic tissue energy consumption and net flux of nutrients, feed intake and digestibility. Portal-drained viscera (PDV) and hepatic energy consumption increased linearly as digestible energy intake (DEI) increased (PDV energy consumption, Mcal/d = 0.2005 + 0.0660 [DEI, Mcal/d], R2 = 22%; hepatic energy consumption, Mcal/d = 0.1457 + 0.0659 [DEI, Mcal/d], R2 = 25%). However, improvements in R2 occurred when other independent variables were included in regressions (PDV energy consumption, Mcal/d = −0.0112 + 0.1859 [DEI, Mcal/d]—0.0254 [DEI2, Mcal/d] + [fecal neutral detergent fiber, kg/d], R2 = 34%; hepatic energy consumption = 0.0014 + 0.0266 [DEI, Mcal/d] + 0.3325 [PDV energy consumption, Mcal/d] + 0.0745 [hepatic urea nitrogen net flux, M/d] + 0.0016 [body weight, kg], R2 = 48%). Splanchnic bed energy consumption as a percentage of DEI was best described (R2 = 49%) by 43.611–9.531 [DEI, Mcal/d] + 15.914 [fecal neutral detergent 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 variation, of which 55 and 45% was attributable to alpha-amino and ammonia nitrogen, respectively. In conclusion, factors besides physiological workload as depicted by DEI accounted for variability in energy consumed by splanchnic tissues with ad libitum ingestion of forage-based diets. The decreasing proportion of DEI attributable to splanchnic bed use may contribute to change in animal performance with increasing DEI.