Abstract: The aim of the present study was to determine the effects of pomace from different grape varieties on the proteolysis and aerobic stability of alfalfa silage. The alfalfa (Medicago sativa) variety “Gannong No.4” was used as the base material for the silage, and pomace of three grape varieties Malbec (MC), Merlot (MT) and Cabernet gernischt (CG) were added at rates of 50, 100 and 150 g·kg^-1, making a total of 10 treatment groups, including a control (CK) without added grape pomace. Silage fermentation quality, protein components, pH, activities of proteolytic enzymes aminopeptidase and carboxypeptidase, microbial counts and aerobic stability were determined. It was found that all grape pomace significantly (P<0.05) reduced the silage pH when added at 100 and 150 g·kg^-1. The non-protein nitrogen content decreased with increasing supplementation rate of the grape pomace. MC added at 150 g·kg^-1 had the lowest non-protein nitrogen content (430.25 g·kg^-1). Adding grape pomace reduced the content of peptide nitrogen in the silage, but peptide nitrogen content did not vary significantly with the rate of pomace added. MT added at 150 g·kg^-1 had the strongest inhibitory effect on silage carboxypeptidase; enzyme activity declined from 17.56 μmol·h^-1 to 6.51 μmol·h^-1. Addition of grape pomaces increased the lactic acid bacteria count after silage fermentation, and inhibited the growth of mold. The highest lactic acid bacteria count was for CG added at 150 g·kg^-1. The number of fungi in CK was 3.02 log₁₀cfu·g^-1, significantly (P<0.05) higher than other treatments. Addition of all three grape pomaces slowed down the rate of fungal spoilage during aerobic exposure and the MT treatment group was stable for the longest time before showing aerobic decay. The above results indicated that the pomace of all three grape varieties improved silage fermentation quality, inhibited activity of silage proteases and reduced the degree of silage protein hydrolysis, and improved the aerobic stability of silage.

Key words: grapes pomace, alfalfa silage, fermentation quality, proteolytic