Data from the N balance study were checked for adherence
to the normal distribution and homogeneity of
variance using histograms and formal statistical tests as
part of the univariate procedure (SAS Institute, 2004).
The relationship between urea N excretion (g/d) and
feed N intake (kg/d) was tested for linear effects using
Proc GLM (SAS Institute, 2004). Analysis of data was
carried out using the repeated measures function in
Proc Mixed (SAS Institute, 2004). The model included
tests for the random effects of cow and the fixed effects
of period, parity, and dietary treatment, and the interaction
between dietary treatments. Where no interactions
were observed for measures taken, this term was
removed and only main effects are reported hereafter.
Statistical significance was assumed at a value of P <
0.05, whereas a tendency toward significance was assumed
at P > 0.05 but