[Protein digestion in ruminant calves]

Area of Science:

• Animal Nutrition
• Ruminant Physiology
• Digestive Metabolism

Background:

• Forestomach nitrogen (N) digestion is crucial for ruminant health and growth.
• Soybean meal is a common protein source, but alternatives are explored.
• Urea and lucerne are potential substitutes for soybean protein in calf diets.

Purpose of the Study:

• To evaluate the impact of different protein sources on nitrogen utilization in young calves.
• To compare the effectiveness of urea-nitrogen and lucerne-nitrogen as replacements for soybean coarse meal-nitrogen.
• To determine optimal protein strategies for calves during their growth phase.

Main Methods:

• Ten 12-week-old calves with duodenal re-entrant cannulae were used.
• Soybean coarse meal-N was replaced by 50% and 100% urea-N (B) or lucerne-N (C).
• Rumen ammonia concentration, pH, bacterial nitrogen synthesis, and duodenal non-ammonia nitrogen flow were measured.

Main Results:

• Rumen ammonia levels were highest with urea-N (18.9 mg/100 ml) and lowest with lucerne-N (4.5 mg/100 ml).
• Duodenal non-ammonia nitrogen flow relative to intake was 90% (A), 79% (B), and 104% (C).
• Complete replacement of soybean protein with lucerne protein ensured adequate protein supply.

Conclusions:

• Partial replacement of soybean coarse meal-N with urea-N is ineffective for 12-week-old calves requiring >17% crude protein.
• Complete substitution of soybean protein with lucerne protein effectively meets the protein requirements for growing calves.
• Lucerne protein is a viable alternative for ensuring adequate protein supply in young calves.