Ruminal escape protein for lightweight feedlot calves

Area of Science:

• Animal Nutrition
• Ruminant Physiology
• Feedlot Cattle Production

Background:

• Ruminal escape protein (REP) is crucial for meeting amino acid requirements in feedlot cattle.
• Understanding the optimal supplementation level of REP is essential for maximizing growth and efficiency.
• The basal diet relied solely on urea for supplemental nitrogen, potentially limiting essential amino acid supply.

Purpose of the Study:

• To evaluate the effects of varying levels of supplemental ruminal escape protein (REP) on feedlot steer performance.
• To determine the impact of REP supplementation on the net energy (NE) value of the diet.
• To assess the postruminal supply of nitrogen and amino acids with REP supplementation.

Main Methods:

• An 84-day growth study with 140 feedlot steers (198 kg initial weight).
• Dietary treatments included a basal diet and basal diet supplemented with 2%, 4%, or 6% REP.
• A site of digestion study was conducted with four steers (149 kg initial weight).

Main Results:

• REP supplementation quadratically affected the rate and efficiency of gain (P < .05).
• The greatest improvement (13.4% rate, 8.4% efficiency) occurred with 2% REP.
• Diet NE increased by 6.6% with 2% REP, and non-ammonia and amino acid N passage to the small intestine increased linearly with REP (P < .01).

Conclusions:

• Supplementing feedlot diets with 2% REP optimized steer performance and diet NE value.
• Postruminal amino acid deficiencies, particularly arginine, histidine, lysine, methionine, and phenylalanine, were identified in the basal diet.
• Excess bypass protein may negatively impact performance by increasing arginine demand for ammonia detoxification.