Efficiency of lysine utilization by growing steers

Area of Science:

• Animal Nutrition
• Ruminant Physiology
• Nutrient Metabolism

Background:

• Lysine (Lys) is a critical limiting amino acid for protein synthesis in ruminants.
• Understanding Lysine utilization efficiency is crucial for optimizing growth and minimizing nitrogen excretion in cattle.

Purpose of the Study:

• To evaluate the efficiency of Lysine utilization by growing steers.
• To determine the optimal level of supplemental Lysine for maximizing nitrogen retention and protein deposition.

Main Methods:

• Five Holstein steers were used in a 6x6 Latin square design, receiving diets low in RUP and abomasally infused with varying levels of Lysine (0-15 g/d).
• Nitrogen balance was measured over 4 days, with blood samples collected for plasma amino acid and urea analysis.
• Diet organic matter digestibility was assessed, and break-point analysis was used to estimate optimal Lysine levels.

Main Results:

• Diet digestibility was not affected by Lysine supplementation.
• Urinary Nitrogen excretion and plasma urea nitrogen decreased with increasing Lysine up to 9 g/d.
• Nitrogen retention increased linearly up to 9 g/d supplemental Lysine, reaching maximal efficiency at 40% for protein deposition.

Conclusions:

• Lysine supplementation significantly improved nitrogen retention in growing steers.
• Optimal supplemental Lysine level for maximal nitrogen retention was determined to be 9 g/d.
• The efficiency of Lysine utilization for protein deposition was estimated at 40%.