Effect of dietary crude protein level on visceral organ mass, cellularity, and the protein expression of Atp synthase, Na + /K + -Atpase, proliferating cell nuclear antigen and ubiquitin in feedlot steers
Twenty-four steers [initial body weight (BW) = 510 ± 4.9 kg] predominately of Angus breeding were used to determine the effect of dietary crude protein (CP) level [8.5, 10.7, 12.3 or 14.5%, dry matter (DM) basis; high-moisture-corn-based diets] on visceral mass, cellularity, and protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen (PCNA) and ubiquitin. Steers were on dietary treatment for 28 d. Kidney, liver, and reticulorumen weights (g) increased linearly (P < 0.05) with increased dietary CP. Lung weight (g; g kg-1 BW) linearly increased (P < 0.05) with increased CP. Ruminal and small intestinal DNA concentration, and the ratios of RNA:DNA and protein:DNA in small intestine were affected quadratically by increased dietary CP (P < 0.05). Hepatic ATP synthase expression was affected quadratically with an increase when dietary CP increased from 8.5 to 10.7%, and a decrease when dietary CP increased from 10.7 to 14.5% (P < 0.05). Renal ATP synthase expression decreased linearly (P < 0.05) and small intestine mucosal Na+/K+-ATPase expression increased linearly (P = 0.05) with increased CP. These results indicate that increasing dietary CP increases liver, kidney, lung, and rumen masses, and differentially influences expression of proteins influencing energy utilization and efficiency in liver, kidney, and small intestine.Key words: Dietary crude protein, visceral organ mass, cellular energy metabolism, steer