Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2008
Publication Date: 7/7/2008
Citation: Brown, K.R., Klotz, J.L., Strickland, J.R., Bush, L.P., Boling, J.A., Matthews, J.C. 2008. Steers Grazing Toxic Neotyphodium Coenophialum-Infected Forages Have Increased Hepatic Gluconeogenic Capacity. J. .Anim. Sci. Vol. 86, E-Suppl. 2. p 101.
Technical Abstract: Impaired growth performance and clinical parameters constituting “summer slump” in cattle grazing toxic endophyte-infected tall fescue are well documented. To test the hypothesis that fescue toxicity affects carbon chain and amino acid N metabolism in the liver of cattle grazing this forage, 19 Angus X steers were randomly assigned to graze either a low-endophyte (LE) mixed grass-tall fescue pasture (n = 9; BW = 266 ± 10.9 kg; 5.7 ha) or a high-endophyte (HE) tall fescue pasture (n = 10; BW = 267 ± 14.5 kg; 5.7 ha) for 89-105 d. Pasture samples were collected on d 37, 59, 88 and 109, pooled, and analyzed for alkaloid content. Blood was collected on d 85 for serum prolactin (PRL) analysis and steers then killed over a 17-d period, with treatment animals equally distributed over d of kill. HE pasture samples contained (µg/g) 24 and 38 times more (P < 0.01) ergovaline (0.322) and lysergic acid (0.065), respectively, than did LE pastures. Serum PRL of HE steers was only (P < 0.01) 10% (3.60 ng/mL) that of LE steers. Whereas liver alanine transaminase content did not differ, aspartate transminase (AST) and cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) content was 56% and 90% greater (P < 0.01), respectively, in HE steers. In contrast, hepatic content of glutamate synthetase, glutamate dehydrogenase, and 3 transport proteins responsible for high-affinity aspartate/glutamate uptake in the liver did not differ. Together, the increased hepatic content of AST and PEPCK-C of HE steers indicates that increased alkaloid challenge, depressed serum PRL, or both, induces a greater capacity for liver gluconeogenesis, met in part through an increased expression of proteins that metabolize aspartate carbons to oxaloacetate and oxaloacetate to phosphoenolpyruvate.