The metabolisable protein system (AFRC, 1992) requires the measurement of the dynamics of the degradation of protein in the rumen. However many drying techniques used during sample preparation cause protein damage and denaturation which may affect the subsequent assessment. The objective of this work was to compare the dry matter and nitrogen degradation profiles of samples of grass silage dried using a range of techniques.

One kilogram samples of first cut grass (Lolium perenne) silage (156 g CP/kg DM) were air dried (AD), freeze dried (FD), dried at 50 (OD50) or 100°C (OD100) in a still air oven or dried in a microwave oven (MD) on the ‘defrost’ setting. In sacco degradability was assessed in fistulated yearling wether sheep, using a 5x5 Latin square and incubation times of 3,6,12,24 and 48 hours. Bags size was nn x nn cm with a sample size of 3 g. Bags were rinsed and frozen upon removal, mechanically washed and dried at 60°C before analysis. Dry matter and nitrogen disappearance data for each sheep was fitted to the model y = a + b(1-e-ct) using non-linear regression.