Performance and serum chemistry profile of lambs fed on rations with increasing levels of urea

Abstract

Feed intake and efficiency, animal performance, and protein and energy metabolism were studied in lambs that were fed on increasing levels of urea (0.0, 0.5, 1.0, and 1.5% of dry matter [DM]). A completely randomized design was used, with four treatments (urea levels) and six replicates. The lambs were fed ad libitum for 56 days until they reached an average body weight of 35 kg. The rations were composed of 34% Tifton 85 hay (Cynodon spp.) and 66% concentrate. Crude protein (CP) constituted 17% of the diet on a dry matter basis, and total digestible nutrients (TDN) accounted for 65%, on average. The dry matter intake (DMI) and crude protein intake (CPI) were not influenced by the urea levels in the diet, presenting average values of 1.175 and 0.206 kg animal-1 day-1, respectively. The average daily gain (ADG), feed conversion ratio (FCR) and gross feed efficiency (GFE) were also not influenced by urea levels (0.225 kg day-1, 5.33 kg DM kg gain-1 and 0.195 kg gain kg DM-1, respectively). Except for urea and glucose concentrations, blood parameters did not change with increasing urea in the diets. The mean values for total protein, albumin, globulin and creatinine in the serum were 7.11 g dL-1, 3.36 g dL-1, 3.75 g dL-1 and 0.91 mg dL-1, respectively. Serum urea decreased linearly and serum glucose increased linearly with urea levels in the diet. The addition of 1.5% of urea to the diets did not change feed intake and efficiency or animal performance, and did not cause metabolic disorders in feedlot lambs in the finishing phase.