Study of modes of preparation of fresh and conserved forage samples for measurement of their dry matter and nitrogen degradations in the rumen

Six trials were conducted to study the conditions of preparation and treatm ent of moist forage samples for the in situ measurement of their ruminal dr y matter and nitrogen degradations. The following preparations were compare d in five trials: Trial I on fresh forages: lacerated fresh before bagging and freezing in liquid nitrogen and then stored at -20 degrees C, forage dr ied at 60 degrees C and ground to 0.8 mm, forage dried at 80 degrees C and ground to 0.8 mm, forage dried at 60 degrees C and ground to 4 mm. Trial II on lacerated fresh forages: put immediately in bags then in numen, frozen in Liquid nitrogen and used immediately, frozen in liquid nitrogen and stor ed at -20 degrees C, freeze dried then stored at -20 degrees C. Trial In: o n silages: lacerated silage, frozen in liquid nitrogen and then stored at - 20 degrees C, silage dried at 80 degrees C and ground to 0.8 mm. Trial IV o n hays: undried ground to 12 or 4 mm, dried at 80 degrees C and ground to 0 .8 mm. Trial V: after ruminal incubation, bags beaten or not with a 'stomac her' after washing and before oven-drying. In trial VI, particle losses thr ough the bag pores were measured. The main objective of all these trials wa s to evaluate a mode of sample preparation of moist materials (fresh and si lage) in two steps: processing in a 'universal mill' to particles in about 5 mm length, bagging and rapid freezing of the bags in liquid nitrogen. The re was no difference between fresh forage placed immediately in the rumen, fresh forage frozen in nitrogen and placed immediately in the rumen, and th e same stored and then used several months later. Drying, even at 60 degree s C, lowered effective nitrogen degradability against moist forage; drying at 80 degrees C lowered it by 10 points (P < 0.01) (1 point = 1% on a scale from 0 to 100). Freeze-drying had a weak negative effect (-3.1 points; P < 0.05). The nitrogen degradability of hays increased with decreasing partic le size (+7.7 points, P < 0.01, from 12 to 0.8 mm mesh size). Beating with a 'stomacher' is useful for reducing microbial contamination of bag residue s (increasing nitrogen degradability by +4.3 points, P < 0.05, for a poorly digestible forage, but only +1 point [not significant] for a digestible on e). Finally, losses of particles through bag pores were low, 1.3% of used d ry matter. The mode of preparation tested is suitable for the study of nitr ogen degradation of moist forages in the rumen. It is therefore recommended that such moist forages be used directly or after freezing in liquid nitro gen without either oven-drying or freeze-drying. ((C) Elsevier / Inra).