Submitted to: Journal of Applied Animal Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/1996
Publication Date: N/A
Interpretive Summary: The gut and liver combined account for approximately one-half of heat lost by ruminants; however, very little is known about what factors influence heat production by the gut and liver. Once such factors are identified and characterized, diets can be designed to minimize wasteful heat production by these tissues and maximize energy and nutrient capture by ruminant tissues of greatest value to U.S. consumers (i.e., lean meat). It was found that diet characteristics influencing the quantity of absorbed energy should influence animal performance in part because of effects on efficiency of gut metabolism rather than solely through change in the quantity of energy absorbed. Characteristics of digesta in the gut affected gut energy use independent of the effect of the quantity of energy absorbed. In addition, the quantity of heat energy generated by the gut had a direct effect on liver production of heat. These results indicate that future research attention should be given to identification and characterization of digesta characteristics responsible for diet effects on gut energy use and the dietary attributes most responsible for these digesta characteristics. In addition, these findings suggest that one cannot accurately predict ruminant productivity and efficiency of production, or most appropriately manage forage for high levels and efficiencies of production, without understanding diet effects on energy and nutrient use by the very metabolically active and costly gut and liver.
Technical Abstract: 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]. 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.