Effects of dietary rumen undegradable protein:rumen degradable protein ratio on nitrogen metabolism in Hanwoo steers.

Objective: We investigated the effects of dietary rumen undegradable protein (RUP):rumen degradable protein (RDP) ratio on growth performance, nitrogen (N) metabolism, and rumen and blood parameters in Hanwoo (Korean cattle) steers.

Methods: Eight Hanwoo steers (average body weight, 393 kg) were allocated to two groups and fed with a high RUP:RDP ratio (46.9:53.1 based on crude protein) or a low RUP:RDP ratio (30.6:69.4) concentrate with iso-crude protein content in a 2×2 Latin square design in two successive periods.

Results: The high RUP:RDP group had higher (p<0.01) average daily gain, and lower (p<0.05) ruminal ammonia and plasma urea N concentrations than the low RUP:RDP group. The high RUP:RDP group had lower (p<0.05) urinary N excretion and urinary N per N intake and higher (p<0.1) tendency of retained N than the low RUP:RDP group. The high RUP:RDP group had higher (p<0.1) tendency of N utilization efficiency (retained N per N intake: 28.7% vs. 25.5%) than the low RUP:RDP group. The high RUP:RDP group had a lower (p<0.1) tendency of urinary N per total N excretion, but a higher tendency of fecal N per total N excretion.

Conclusion: A high ratio of dietary RUP:RDP may improve N utilization efficiency by reducing urinary N excretion, which may be beneficial for the environment through reducing atmospheric ammonia emissions.