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

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