Statistical modelling /Concentrates and milk yield

A summary of the regression coefficients for each phase of lactation, together with the correlation coefficients, is shown in the table below. Each correlation coefficient was calculated by taking the square root of the 'Percentage variance accounted for' divided by 100 in the linear regression output of GenStat.

The table shows that the strongest association was in Phase 2 of lactation (r=0.73).

The full regression equation for the average values was found to be:

Milkaverage = 2.75 (± 1.15) + 2.18 (± 0.23) concaverage

This is very similar to the equation shown in Figure 3 of Romney et al. The regression coefficient for Phase 2 was similar to the average regression coefficient across the whole of lactation. Thereafter, the regression coefficient decreased in value.