Degradation kinetics of leaves, petioles and stems of forage rape (Brassica napus) as affected by maturity

A study was conducted with rumen-fistulated sheep to measure changes in the degradation characteristics of forage rape leaf, petiole and stem at seven consecutive weeks of maturity. Forage rape plants were harvested randomly every week and separated into leaf, petiole and stem fractions, which were chopped into 1-2 cm pieces and incubated individually in the rumen of fistulated sheep. An increase in dry matter (DM) and fibre content, with a decrease in crude protein (CP) content, was evident among forage rape fractions, particularly stem, with advancing maturity. Among all plant fractions, extent of degradation of organic matter (OM), CP and fibre decreased (P<0.001) with maturity. There were plant fraction and maturity interactions for the soluble fraction, slowly degradable fraction, rate of degradation and effective rumen degradability. Rate of degradation of fibre decreased from week 7 until 13 in forage rape leaf (0.21-0.08/h), petioles (0.12-0.03/h) and stem (0.09-0.01/h). However, results quantified the relatively high CP, and lower fibre contents, as well as the faster ruminal degradation of leaf > petiole > stem. The nutritive value of forage rape decreased with advancing maturity, although the quality of leaves in particular remained high from week 7 until 13 of maturity.