Fermentation characteristics, aerobic stability, proteolysis and lipid composition of alfalfa silage ensiled with apple or grape pomace

• Apple and grape pomaces are the by-products from cider and red wine industries.
• Both pomaces are rich in various polyphnenols and unsaturated fatty acids.
• Including apple or grape pomace in alfalfa at ensiling reduced soluble N content of silage.
• Including both pomaces in alfalfa at ensiling also altered the fatty acid composition of silage.

The effects of adding 100 g of either dried apple pomace (AP), unground grape pomace (GP) or ground grape pomace (GGP) per kg wilted alfalfa (wet basis) on silage characteristics, aerobic stability, proteolysis and lipid composition were studied. The three combinations as well alfalfa without addition were ensiled in 1.8 L- jars for 60 d, with 4 jars per treatment. Addition of AP and GGP decreased pH (P<0.05). Pomace-treated silages contained more lactic acid than the control silage. Pomace treatments decreased aerobic stability of the ensiled alfalfa. The nonprotein nitrogen (NPN) concentrations in the ensiled alfalfa were decreased by 54%, 67% and 69% after being ensiled with AP, GP and GGP, respectively. Total fatty acid concentrations in the control silage and AP silage were comparable, but in GP or GGP-treated silages it was more than double that of the control silage. Application of pomace markedly increased (P<0.05) the proportions of oleic acid and linoleic acid in the ensiled alfalfa due to high proportions of these fatty acids in both pomaces. Silages treated by GP or GGP had a much greater proportion of linoleic acid than the control or AP treated silages (P<0.05); this fatty acid accounted for half of the fatty acids in GP or GGP-treated silages. The proportion of α-linolenic acid was lower in GP or GGP silages than in control silage or AP silage (P<0.05). In conclusion, application of apple or grape pomace at ensiling of alfalfa could not only employ this industrial waste as feed, but also inhibit proteolysis and alter the fatty acid composition of ensiled alfalfa.