COMPOSICION QUIMICA Y DIGESTIBILIDAD IN VIVO DE ENSILAJE DE BALLICA ITALIANA (L. multiflorum Lam., cv. Concord) EN CUATRO ESTADOS FENOLOGICOS

Abstract

The purpose of this study was to evaluate the effect of the phenological stage at harvesting on the chemical composition and in vivo digestibility of dry matter (DMD) and both digestible (DE) and metabolizable (ME) energy content of silage made from a sward of Italian ryegrass (Lolium multiflorum, cv. Concord). Grass was harvested at four stages: pre-inflorescence emergence, early spike emergence, early flowering (anthesis) and milky grain. Four male calves of ca. 200 kg liveweight were used in sequential metabolic trials, with intake restricted to 70% of ad. lib. and with total collection of faeces and urine. Fresh grass and silages were analysed for dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and ME estimated in vitro. As fresh grass matured, its DM concentration increased from 13.6 to 29.5%, NDF from 50.8 to 60.9% and ADF from 30.6 to 39.5%. CP and ME were reduced from 13.4 to 7.8% and from 2.44 to 2.19 Mcal/kg DM, respectively. The resulting silage increased DM (from 14.4 to 25.2%, oven basis) and decreased CP (from 12.9 to 9.1%). NDF varied from 58.7 to 63.3% and ADF from 39.3 to 41.1 %. Both fibre fractions failed to exhibit a consisten! trend with maturity. ME estimated in vitro changed from 2.25 to 2.16 Mca/kg DM. In vivo DMD decreased as growing period of pasture increased, from 65.4 to 54.2%. Same trend was found for DE which decreased from 2.91 to 2.31 Mcal/ kg DM (oven basis) and for ME which declined from 2.23 to 1.82 Mcal/kg DM (oven basis). Both DE and ME presented higher values (ca. 0.3 Mcal/kg DM) when expressed on a toluene DM basis. ME/DE ratio was slighty lower in an earlier (0.78) compared to a later (0.81) growth stage. It is concluded that silage harvesting should not exceed the spike emergence stage.