Ruminal ammonia load affects leucine utilization by growing steers

Area of Science:

• Animal Nutrition
• Ruminant Physiology
• Nutrient Metabolism

Background:

• Leucine (Leu) is an essential amino acid crucial for protein synthesis in growing animals.
• Ruminal ammonia is a nitrogen source for microbial protein synthesis but can also influence host nitrogen utilization.
• Understanding the interplay between ruminal ammonia and essential amino acid utilization is vital for optimizing animal growth and feed efficiency.

Purpose of the Study:

• To investigate the effects of varying ruminal ammonia loads on leucine utilization and whole-body protein deposition in Holstein steers.
• To determine if increased ruminal ammonia enhances the efficiency of supplemental leucine in growing cattle.

Main Methods:

• A 6x6 Latin square design with six Holstein steers was employed.
• Steers received a basal diet supplemented with abomasal infusions of glucose and essential amino acids (except Leu).
• Treatments involved factorial arrangement of abomasal Leu infusions (0, 4, or 8 g/d) and ruminal urea infusions (0 or 80 g/d).

Main Results:

• Abomasal Leu infusion linearly decreased urinary and fecal nitrogen excretion and increased nitrogen retention.
• Ruminal urea infusion increased plasma urea, urinary nitrogen, and urinary urea excretions, but also significantly increased retained nitrogen.
• The efficiency of supplemental Leu deposition ranged from 24% to 43%, being higher with urea infusion.

Conclusions:

• Increasing ruminal ammonia load improved whole-body protein deposition in growing steers when leucine supply was limiting.
• Elevated ammonia levels enhanced the utilization of supplemental leucine for protein accretion under these experimental conditions.
• These findings suggest a potential benefit of managing ruminal nitrogen to optimize essential amino acid efficacy in cattle diets.