Estimate of the nutritive value of maize silage

In order to check and improve the prediction of their nutritive value, 12 maize silages were studied as a supplement to the previous trials. Two varieties (Amadeo and LG32,52) were harvested at three different stages over the course of two years. The silages were studied to determine organic-matter digestibility (OMD) in the case of sheep, and nitrogen degradability (ND) in the case of fistulated cows. The chemical compositions differed more between years than between varieties. The OMDs of the plants increased with maturity, with the milky stage differing (p<0,01) from the two wax-ripe stages (69,1 % vs. 74,9 % and 76,8 %), without distinction between the two varieties, whilst the ND decreased. In the hard-dough stage, the coefficient was lower (66,5 %, p<0.01) than that of the other stages (76,5 % for the milky and 77,8 % for the soft-dough stage, respectively). The ND of the two varieties was similar (p=0,4). The differences between the nutritive values calculated from coefficients determined or estimated by equations varied from + 2 % to – 14,6 % for the NELs and from + 9 % to -16,6 % for the PAIEs. A new equation for OMD and a correction of the estimated OMD are proposed in order to reduce the residual standard deviations. The predicted values will remain approximative values which must be used with great care.