Effects of varying dietary undegradable protein on dry matter intake, growth, and carcass composition of Holstein calves.

The objective was to study the effect of feeding diets varying in rumen undegradable protein on DMI, growth, feed efficiency, and carcass composition in Holstein calves from birth to 25 wk of age. Sixty Holstein calves were assigned in a randomized complete block design to one of three dietary treatment groups that differed in rumen undegradable protein as a percentage of total protein. Protein undegradabilities of the TMR fed for ad libitum intake for period 1 (wk 1 to 12 of age) were 33, 37, and 46% and for period 2 (wk 14 to 25 of age) were 30, 34, and 38%. Intake was not different among diets during period 1. During period 2, animals fed the highest and lowest levels of undegradable protein diet consumed less DM, and those animals on the highest undegradable diet had the least amount of crude protein intake. Feed efficiency was increased with increasing rumen undegradable protein for period 2. Carcass composition was not affected by dietary treatment for either 9-10-11 rib section or the half carcass. Prediction equations for carcass protein and fat were calculated for 25-wk Holstein calves using urea space and live weight. These results indicate that the amount of undegradable intake protein currently recommended for growing dairy replacements may not be justified when intake is ad libitum. In the present study, urea space was not found to be beneficial over live weight for predicting carcass protein and fat in intact male or female Holstein calves.