Effect of dietary factors on visceral organ mass and expression of proteins regulating cellular energy metabolism in feedlot steers

Three experiments were conducted to determine the influence of dry matter intake (DMI; 1.25, 1.50, 1.75, and 2.00 % of BW), crude protein density (CP; 8.8, 11.0, 13.2 and 15.4%; DM basis), and corn silage inclusion (CS; 20, 40, 60, and 80% of corn silage; DM basis) on visceral tissue mass, cellularity and protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen (PCNA) and ubiquitin in feedlot steers. Twenty-four yearling steers (467 +/- 3.6, 510 +/- 4.9, and 535 +/- 5.0 kg initial BW for DMI, CP and CS experiment, respectively), predominately of Angus breeding, were used in each experiment in a randomized block design and individually fed for at least 28 d before tissue collection. Increasing DMI, CP and CS resulted in increased total digestive tract mass. The absolute mass of lung, liver, kidney and reticulorumen increased linearly by increasing DMI and CP; however, there was no individual organ mass response to CS. Hepatic PCNA expression increased linearly as DMI increased. PCNA expression was affected quadratically in pancreas, small intestinal mucosa and sternomandibularis muscle by DMI. ATP synthase, Na+/K+-ATPase and ubiquitin expression in pancreas and ubiquitin expression in small intestinal mucosa increased linearly as DMI increased. Hepatic ATP synthase expression increased when CP increased from 8.5% to 10.7%, and decreased when dietary CP increased from 10.7% to 14.5%. Renal ATP synthase expression decreased linearly and small intestine mucosal Na+/K+-ATPase expression increased linearly with increasing CP. Hepatic Na+/K +-ATPase expression linearly increased and ruminal Na+/K +-ATPase expression linearly decreased with increasing CS. Hepatic PCNA decreased when CS increased from 20% to 60% and increased when CS increased from 60% to 80%. Renal ATP synthase and ubiquitin expression increased when CS increased from 20% to 60% and decreased when CS increased from 60% to 80%. These results indicate that DMI, CP and CS influence visceral mass and cellularity and the expression of proteins associated with ATP production and utilization in liver, kidney, rumen, and small intestine. The different responses of mass and specific protein expression for organs demonstrate the complexity of the regulation of energy metabolism in tissues and the whole body.