Predicting ruminally undegraded and microbial protein flows from the rumen

Area of Science:

• Ruminant nutrition
• Protein metabolism
• Feed evaluation

Background:

• The NRC (2001) model for predicting rumen-undegradable protein (RUP) exhibits significant slope bias.
• Existing methods for estimating protein degradation and passage rates may be inaccurate.

Purpose of the Study:

• Identify and correct the linear bias in RUP prediction equations.
• Investigate the impact of rumen-degradable protein (RDP) on microbial nitrogen (MiN) outflow.

Main Methods:

• Adjusted passage rate (Kp) by feed class and in situ degradation rate (Kd) to resolve RUP bias.
• Analyzed ruminal nitrogen flow using compartmental analysis.
• Examined relationships between nutrient intake and microbial N flow.

Main Results:

• Adjusting Kp and Kd resolved RUP prediction bias, indicating in situ Kd and marker-based Kp are biased.
• Microbial N flow is linearly related to ruminally degraded starch, NDF, RDP, and forage NDF intake.
• Revised RUP and MiN predictions improved amino acid flow predictions, though some bias remained.

Conclusions:

• In situ degradation and marker-based passage rates require significant adjustments for accurate RUP prediction.
• RDP and degraded carbohydrates are key drivers of microbial N synthesis in the rumen.
• The revised prediction system offers substantial improvements over previous models for ruminant nutrition.