According to Chen and Gomes (1995), N excretion and retention could reflect on differences in N metabolism
because nitrogen retention was the most important index of the protein nutrition status in ruminants (Ørskov et al., 1999).
In this study, it was observed that positive nitrogen retention was obtained in the treatments when MUP was supplemented.
These values indicated that all treatments had more protein and therefore, higher protein available for use by cattle when
supplemented with MUP as compared with the control