Performance of growing and finishing cattle supplemented with a slow-rlease urea product and urea

Abstract

Two growth trials were conducted to study the performance of Angus Crossbred steers supplemented with a slow-release urea product (Optigen® 1200, O) and urea (U). The base diets were composed of corn silage alone during the growth period and corn silage plus cracked corn during the finishing period. Trial 1 consisted of 40 animals [272 ± 4 kg body weight (BW)] individually fed the base diets and six treatments, which were based on corn silage alone and cracked corn supplemented with U or O to supply 50 (U50, O50) or 100% (U100, O100) of the ruminal N deficiency (U50, O50, U100, and O100) as predicted by the Cornell Net Carbohydrate and Protein System (CNCPS), or with U and O each supplying half of the CNCPS predicted N deficiency (U25O25). In trial 2, 120 pen-fed animals (241 ± 7 kg BW) received the base diets and four combinations of U and O ( U100O0, U66O34, U34O66, and U0O100), which were designed to supply 100% of the ruminal N deficiency predicted by the CNCPS. In trial 1, no differences (P > 0.05) in performance were observed between the U100 and O100 treatments, but animals in the U50 treatment had a greater average daily gain (ADG) (P < 0.05) and feed conversion (P < 0.05) than animals on O50 treatment. In trial 2, combinations of U and O did not affect animal performance (P > 0.05). No differences were observed in carcass characteristics and predicted carcass and empty body fat for both trials (P > 0.05). We concluded there was no improvement in animal performance when urea was substituted by a slow-release urea/NH3 product at levels normally found in feedlot cattle diets. Key words: Cornell net carbohydrate and protein system, modeling, nutrition, growth, non-protein nitrogen