Growth performance of lambs fed diets supplemented with slow-release urea microencapsulated using palm wax (Elaeis guineensis)

Abstract

Non-protein nitrogen (NPN), such as urea, is used daily in ruminant nutrition due to its low cost and ability to meet protein requirements partially. However, improper administration can lead to ammonia toxicity, resulting from the rapid degradation and conversion of urea in the rumen. Urea encapsulation techniques have been developed to reduce this risk and enhance efficiency. These technologies enable a controlled release of nitrogen, synchronizing its availability with ruminal fermentation and improving microbial utilization. This study aimed to evaluate the performance of 40 male Santa Inês lambs, with an initial body weight of 18 kg and an average age of 7 months, distributed in a completely randomized design with four dietary treatments (10 replicates each). The treatments consisted of the inclusion of 1.5%, 2.5%, and 3.5% (on a dry matter basis) of slow-release urea (SRU), compared to a control diet containing 1.5% free urea (FU). The SRU was microencapsulated using the fusion-emulsification method with palm wax (Elaeis guineensis) as the encapsulating agent. For 70 days, the lambs were fed a 40% Tifton-85 hay diet as roughage and 60% concentrate based on corn, soybean meal, mineral mix, and the respective urea source (FU or SRU). Body weights were recorded at the beginning and end of the trial. Including 1.5% FU and SRU resulted in higher final body weight, total weight gain, and average daily gain than the higher SRU levels (P < 0.0001). Increasing the SRU inclusion to 2.5% and 3.5% led to a marked decline in lamb performance, suggesting that these higher doses impaired growth. Therefore, microencapsulated SRU at these levels was not effective and is not recommended as a dietary alternative for finishing lambs.