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 disappearance from dacron bags placed in the rumen and the amount of various N products (total nitrogen (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 addition 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 vegetative 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 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 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 nitrogen disappearing from the nylon bags placed in the rumen. There was little difference linked to the vegetation 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 Ann. Zootech. 49 (2000) [461][462][463][464][465][466][467][468][469][470][471][472][473][474] 461

Protein degradation in the rumen of red clover forage at various stages of growth and conserved as silage or wrapped big bales

“…However, a part of the solubilised nitrogen remained as protein-N for 1 h and 2 h in the rumen after feeding fresh red clover, as we had observed previously [5,6].…”

“…g -1 ) of tN, NH3-N and protein-N in the rumen fluid for red clover fresh forage harvested at the 1st growth stage (first flower), silage + formic acid and wrapped big bale, before the morning meal (T 0 h) and 1 h, 2 h, 4 h, and 7 h after the meal. the mean value of N constituents were lower than those we obtained for lucerne [6], and comparable to the results for ryegrass and cocksfoot for the different preserving methods (unpublished results). The NH3-N/tN ratio represented about 45%, 1 and 2 h after feeding, for fresh forages harvested at different growth stages, and for preserved forages as silage and wrapped big bales.…”

“…In addition, the ratio of leaf tissue was higher for red clover (84%) than for lucerne (65%). The data of Coblentz et al [14] showed that the degradability of lucerne and red clover are similar while in our results [6], red clover was less degraded than lucerne. Nocek and Grant [39], Albrecht and Broderick [2], Le Goffe et al [30], Hvelplund and Weisberg [27] and Hoffman et al [23] also reported that red clover has a lower nitrogen degradation than lucerne.…”

“…Previous experiments have demonstrated the effect of the growth stage and conservation method of lucerne (Medicago sativa) [6], cocksfoot (Dactylis glomerata) and perennial ryegrass (Lolium perenne) (unpublished results) on protein degradation in the rumen. The present study was designed to investigate the effects of the growth stage and various methods of conservation (silage and wrapped big bales) on the ruminal in situ degradation of nitrogen (DegN) for red clover.…”

“…From our results of NAN content at the different kinetic times (0 h, 1 h, 2 h, 4 h, 7 h), the NAN flow was calculated as the area under the curve, extended to 12 h and then multiplied by 2 to include the evening meal [6]. The volume of the liquid phase of the rumen was calculated as described in Section 2.5.…”