Growth and Nitrogen Balance of Calves Fed Rations of Varying Nitrogen Degradability and Physical Form

Effects of degradable nitrogen and ration physical form on dry matter intake, gain, feed efficiency, and digestibility were tested in a 3 x 3 factorial arrangement of treatments in a completely randomized design with 54 male Holstein caIves. Nine rations were formulated from data obtained via the bag technique. Calves were fed from 8 to 20 wk of age. Three calves from each treatment were in a nitrogen balance study, and digestibilities of dry matter and nitrogen as well as nitrogen retention were measured. Calves fed all-concentrate rations had greater digestibility and nitrogen retention than calves fed rations containing hay. Calves fed chopped hay consumed less dry matter and gained less than calves fed either ground hay or all-concentrate rations. Feed efficiency was highest for calves fed all-concentrate rations. Nitrogen degradability did not affect dry matter intake, weight gain, or feed efficiency. Calves fed rations with the lowest degradable nitrogen retained more nitrogen per unit of metabolic body size and utilized nitrogen more efficiently than calves fed rations containing higher ruminal degradable nitrogen although not always significantly more. Protein degradation determined by the bag technique may have potential for formulating rations to improve efficiency of nitrogen utilization.