Degradation in the rumen of proteins from fresh lucerne forage in various stages of growth and conserved as silage or hay

The extent to which rumen soluble nitrogen can contribute to the intestinal flow is unknown. Therefore a study was carried out to simultaneously asses s the dynamics of protein disappearance from dacron bags placed in the rume n and the amount of various N products (total nitrogen (tN), ammonia nitrog en (NH3-N), non-ammonia nitrogen (NAN). Measurements were carried out on 4 sheep fed various lucerne forages. These forages included fresh lucerne cut at the vegetative or bud stage, fresh lucerne cut at the 6-week second gro wth stage and at stemmy regrowth stage. In addition two silages made from l ucerne at the bud stage, with or without formic acid were also given. The h ay was dried on the ground in good weather. The effective degradability of nitrogen (DegN) estimated from the nylon bag procedure was lower (p < 0.05) with the latter vegetation stage (0.80 for vegetative stage vs. 0.76 for b ud stage). This value was 0.81 for the regrowth stage. The DegN of the sila ges was higher (p < 0.05) without additive (0.84) than with formic acid (0. 80) and the DegN of the hay was markedly lower (0.66, p < 0.05) than with t he original fresh forage. Whatever the forage studied, tN and NAN rumen flu id contents were high at 1 h or 2 h after feeding (from 0.458 mg.g(-1) for hay to 0.813 mg.g(-1) for fresh forage at the vegetative stage) and diminis hed rapidly up to 7 h after feeding except for the silages, for which the m inimum content was observed 4 h after feeding. A part of the solubilised ni trogen remained as proteins at 1 h and 2 h after feeding for fresh lucerne at various stages of harvesting (from 0.187 mg.g(-1) to 0.221 mg.g(-1) at 1 h) while no protein could be seen in the rumen fluid after feeding of shee p fed silage (with or without preservative) or hay. The part of NAN escapin g rumen degradation and transiting with the rumen fluid represented 7 to 11 % of the nitrogen disappearing from the nylon bags placed in the rumen. The re was little difference linked to the vegetation stage of the forage or it s mode of conservation in particular. This content remained high for hay wh ile its effective degradability (0.66) was much lower than for other forage s (from 0.76 to 0.84).