Energy Supply of Dietary Nutrients and Utilization of Energy and Nitrogen by Early Weaned Calves up to 17 Weeks of Age

Abstract

Balances of energy and dietary nutrients were determined in20 Holstein castrated male calves, at the ages of9, 13and17weeks, to study the efficiency of the utilization of metabolizable energy (ME) and nitrogen (N), and to estimate the amounts of energy supplied by the nutrients for growing calves weighing less than100kg.Balance trials were carried out at9, 13 and 17weeks of age using2levels of feeding (twice and1.5times of maintanance).The following results were obtained: 1) There were no systematic trends in the coefficients of digestibility for N, residual organic matter, calculated by sutracting crude protein from organic matter (ROM) and gross energy (GE), with the age of calves and level of feeding.There were no trends for the metabolizability of GE either.2) The efficiency of utilization of ME for growing calves was calculated via the following regression equation;Energy retention (ER, kJ/kg^0.75) =0.6 (±0.04) ME-244.3) The regression of N retention (Nr, g/kg^0.75) on ER (MJ/kg0.75) was as follows;Nr=1.83 (±0.20) ER+0.375.4) The results of multiple regression analyses of energy supply on dietary and digestible nutrients showed that ROM decreasingly contributed to each energy partition, while N constantly contributed to it.5) The intakes of either ROM and N or digestible ROM and N were concluded to allow us to estimate the supply of digestible and metabolizable energy with high accuracy.