Leucaena leucocephala (Lam.) de Wit as protein supply for heifers

Objective: To estimate the percentage of Leucaena in the diet of heifers fed with Taiwan grass, in order to maximize the efficiency of the ruminal supply of microbial Nitrogen (ERSMN). Design/Methodology/Approach: Five heifers were randomly selected for each of the five treatments (0, 20, 40, 60, and 80% supplementation with Leucaena), according to a 5×5 Latin square experimental design. We determined the ruminal supply of microbial nitrogen (RSMN), ERSMN, and the urea-N by measuring N and purine derivatives in urine. Subsequently, we predicted the duodenal RSMN, the rumen nitrogen balance (RNB), and the urea cost with the Large Ruminant Nutrition System (LRNS v. 1.0.33) model. Results: The inclusion of Leucaena improved (P≤0.05) the RSMN. The ERSMN estimated by purine derivatives had a quadratic response (P≤0.05) at the inclusion level of Leucaena in the diet. The RNB, the cost of urea, and the urea-N increased (P≤0.05) with a higher inclusion percentage of Leucaena. The maximum ERSMN and N balance were obtained with 20% Leucaena in the ration. Study Limitations/Implications: The expression of the nitrogen utilization potential of Leucaena for microbial protein synthesis in this study was likely restricted by the limited availability of non-fiber carbohydrates (NFC). Further studies must be conducted to determine the most affordable source of NFC to match Leucaena nitrogen utilization in the rumen. Findings/Conclusions: Leucaena could be used as an efficient protein source for heifers at a 20% inclusion in their diet