Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 11/16/2004
Publication Date: 3/22/2005
Citation: Archibeque, S.L., Freetly, H.C., Ferrell, C.L. 2005. Metabolite fluxes across splanchnic tissues in response to varying dietary protein in mature ewes consuming low quality forage [abstract]. Journal of Animal Science. 83(Suppl. 2)90.
Technical Abstract: We hypothesized that there would be nonlinear relationships between nutrient fluxes and dietary protein intake. Fourteen mature Dorsett ewes (72.3, SD 3.8 kg) were used to describe the responses of metabolite flux across the portal drained viscera (PDV) and total splanchnic tissues of mature ewes fed a low quality forage (brome hay and wheat straw) that was supplemented to provide adequate energy for maintenance, yet differing amounts of dietary protein (34 to 122 g/d). The ewes were fed twice daily and metabolite fluxes were observed for the 12 diurnal hours. There were no significant (P > 0.15) quadratic responses of metabolites to increased dietary protein intake. The PDV release of alpha-amino nitrogen did not increase linearly (P = 0.16) with increased protein intake, yet hepatic uptake of alpha-amino nitrogen did increase linearly (P = 0.07) protein intake. Similarly, there was a positive relationship (P < 0.01) between PDV ammonia nitrogen release and dietary protein intake [(0.19 mmol x h**-1) x g protein**-1]. This increase in ammonia absorption from the gut was accompanied by an increased (P < 0.01) uptake of ammonia nitrogen by the liver [(0.17 mmol x h**-1) x g protein**-1] and an increase (P < 0.01) in hepatic urea nitrogen production [(0.16 mmol x h**-1) x g protein**-1]. There was no change (P > 0.19) in total splanchnic or PDV urea nitrogen flux with increased dietary protein. Total splanchnic lactate release also had a positive linear relationship (P = 0.03) with increased dietary protein [(0.22 mmol x h**-1) x g protein**-1]. While nutrient fluxes did respond to increased dietary protein as expected, we failed to prove our hypothesis that there were curvilinear responses in nutrient fluxes as dietary protein intake increased from 34 to 122 g/d in mature Dorsett ewes. However, we did demonstrate that over a very wide range of dietary nitrogen intake, that approximately 40% of each increased g of daily protein intake was converted to ammonia to be converted into urea and either recycled or excreted into the environment.