In Situ Degradability of Fresh Grass Conserved Under Different Harvesting Methods

¹ Research Station, Agriculture Canada, PO Box 90, Lennoxville, PQ, Canada J1M 1Z3
² Experimental Farm, Agriculture Canada, Normandin, PQ, Canada G0W 2E0

The effects of forage conservation and harvesting method on DM and CP degradability of grass cut at the boot stage were determined using nylon bags incubated in the rumen of two fistulated lactating cows. Samples of fresh grass, wilted grass prior to and after ensiling in a stack silo and cut with either a cylinder-type forage harvester (11.3 mm of length cut) or a self-loading wagon (42.4 mm of length cut), wilted grass prior to and after ensiling in large round bales, and grass hay were obtained from the same field and used for determination of DM and CP degradability. The DM-soluble fraction of fresh grass was significantly lower than that of wilted grass and silage, but it was higher than that of hay. In general, the potentially degradable fraction of all treatments was related inversely to the readily soluble fraction in water. The effective degradability of DM of fresh grass was similar to that of hay but was lower than that of wilted grass and silage. The effective degradability of DM of silage was higher than that of wilted grass and hay. The disappearance rate of CP of fresh grass was similar to that of wilted grass, hay, and silage. Silage had a lower disappearance rate of CP than wilted grass. The effective degradability of CP was similar for fresh and wilted grasses. Protein degradabiity was greater for silages than for fresh and wilted grasses. Protein degradability of hay was similar to that of fresh grass and wilted grass. These data suggest that hay and fresh grass have a greater potential for more undegraded protein to leave the rumen than silages and that proteolysis occurs more during silage fermentation than during wilting.

Key Words: forage • degradability • protein • nylon bag

Submitted on July 29, 1991
Accepted on October 15, 1991

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