EFFECT OF MATURITY STAGE OF ITALIAN RYE GRASS AND LUCERNE ON RUMINAL NITROGEN DEGRADABILITY

Ruminal N degradability of Italian rye grass and lucerne was studied using the nylon bag technique: 5 samples of rye grass and 5 of lucerne were harvested during the lst cycle of growth at different stages of maturity, between the leafy stage and the end of heading for rye grass and between the vegetative stage and the end of budding for lucerne. For grass, degradability values were high at the beginning of growth, with a mean of 72.2% in the period from leafy stage to heading, but they decreased rapidly after this stage to 64.6% (of 1. 1%/d). For lucerne, the decrease in N degradability was approximately linear between the vegetative stage (79.0%) and the end of budding (70.0%), a decrease of 0.3%/d. After correction to take into account microbial contamination of bag residues, the reduction of N degradability with stage of maturity appears smaller, ie 5% for rye grass and 4% for lucerne.