The effect of method of forage preservation on the protein degradability and microbial protein synthesis in the rumen

Direct cut silage (DC), formic acid treated silage (FA), wilted silage (W), highly wilted silage (HW) and hay (H) were prepared from the same parental grass. In one experiment, the five diets were fed to sheep and the efficiency of rumen microbial protein synthesis and rumen digesta passage rate were determined. In a second experiment, organic matter and protein degradability characteristics in the rumen of sheep were determined by the in sacco method. Microbial protein supply (MN) was significantly higher (P < 0.05) in HW and H (12.63 and 12.77 g N kg−1 DM intake) than in DC, FA and W (11.09, 11.32 and 10.89 g N kg−1 DM intake). MN tended to be negatively correlated to the concentration of total acids in the feeds (r = −0.73, P > 0.1). There were no significant differences in the digesta passage rates. Effective protein degradability (EDGCP) were 855, 800, 796, 750 and 677 g kg−1 for DC, FA, W, HW and H, respectively. Effective organic matter degradability (EDGOM) for DC, FA, W, HW and H were 552, 517, 526, 484 and 522 g kg−1, respectively. A synchrony index (IS), which takes into account the rate of degradation of nitrogen and organic matter, was calculated. The index varied significantly among the different preservation treatments (0.22, 0.34, 0.28, 0.35 and 0.87 in DC, FA, W, HW and H, respectively). MN tended to be positively correlated to IS (r = 0.72, P > 0.1). Estimated metabolizable protein concentrations were 53.4, 59.9, 57.1, 70.3 and 75.3 g kg−1 DM for DC, FA, W, HW and H, respectively. It was concluded that, based on the protein value, hay was better than silages and wilted silages better than unwilted silages ensiled without an additive. The protein value of silages can be increased by the formic acid treatment prior to ensiling.