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

Abstract

The extent to which rumen soluble nitrogen can contribute to the intestinal flow is unknown. Therefore a study was carried out to simultaneously assess the dynamics of protein dis- appearance from dacron bags placed in the rumen and the amount of various N products (total nitro- gen (tN), ammonia nitrogen (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 growth stage and at stemmy regrowth stage. In addi- tion two silages made from lucerne at the bud stage, with or without formic acid were also given. The hay 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 vegeta- tive stage vs. 0.76 for bud stage). This value was 0.81 for the regrowth stage. The DegN of the silages 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 the original fresh forage. Whatever the forage studied, tN and NAN rumen fluid 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 diminished rapidly up to 7 h after feeding except for the silages, for which the minimum content was observed 4 h after feeding. A part of the solubilised nitrogen remained as proteins at 1 h and 2 h after feeding for fresh lucerne at var- ious 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 sheep fed silage (with or without preservative) or hay. The part of NAN escaping rumen degradation and transiting with the rumen fluid represented 7 to 11% of the nitro- gen disappearing from the nylon bags placed in the rumen. There was little difference linked to the veg- etation stage of the forage or its mode of conservation in particular. This content remained high for hay while its effective degradability (0.66) was much lower than for other forages (from 0.76 to 0.84). lucerne / green forage / silages / hay / vegetation stage / protein degradation / rumen fluid composition