Effect of maize crop maturity on silage chemical composition and digestibility (in vivo, in situ and in vitro)

The effect of maize crop (Suco®, Novartis) maturity: silking (dry matter (DM) content=0.20), milk (M; 0.26 DM content) and half milk line ((1/2)ML; 0.32 DM content), on whole plant silage chemical composition and digestibility, measured in vivo, in situ and in vitro, was evaluated. The in vivo digestibility (DM and neutral detergent fibre, NDF) was measured in nine lambs fed at maintenance (three replicated 3×3 Latin squares). The in situ digestibility (48 h incubation in the rumen of a fistulated cow) and the in vitro digestibility (two-stage procedure) were measured in 10 samples of each silage. Crop maturity increased (P<0.05) silage starch content (0.02–0.28 DM), decreased (P<0.05) NDF content (0.60–0.41 DM) and its digestibility (0.48–0.24), without affecting lignin (0.03 DM) or DM digestibility (0.57 DM). The in vitro and the in situ DM digestibility (0.61 and 0.60, respectively) overestimated by 0.15 (P<0.05) the in vivo DM digestibility (0.53) and the in vivo NDF digestibility was 0.31 higher than the in vitro NDF digestibility. It was concluded that silage in vivo DM digestibility remained constant with maturity because the depression in NDF digestibility was compensated by starch accumulation in the grain and that the in vitro technique or the in situ 48 h incubation in the rumen over-predicted by 0.15 silage DM digestion in vivo.