| Sumario: | A metabolism trial on nitrogen and energy utilization was conducted using thirty male crossbred calves blocked by age and randomly assigned to one of the dietary treatment consisting of ad libitum tef straw alone or supplemented with three levels (0.5, 1 and 1.5 percent of the body weight) of cowpea or lablab hay. Supplementation and increasing the level to the supplements increased the intake of nitrogen, the excretion of faecal and urinary nitrogen, N digestibility and the amount of nitrogen retained the calves. Moreover, the intakes of gross and digestible energy and urinary energy output increased in response to supplementation and increasing levels of the supplements. The supplement types had a similar effect on nitrogen and energy utilization. In conclusion, tef straw, when fed alone, cannot maintain nitrogen equilibrium. Therefore, it requires supplementation.
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