The effect of long -term grass silage storage on its nutritive value and quality

Abstract

Italian ryegrass was cut on 10^th May 1988 and ensiled in experimental silo (100 l) either directly (S/0) or after wilting for 6 (S/6), 10 (S/10), 30 (S/30) or 34 (S/34) hours. Dry matter (DM) concentration increased from 190 g kg^-1 at cutting time to 230, 267, 376 and 434 g kg^-1 after 6, 10, 30 and 36 hours of wilting. Formic acid treated silage (4 g of 85 % formic acid per kg) was also prepared from unwilted grass (S/0 MK). The silos were opened after 12 years. The silages S/0, S/0 MK, S/6, S/10, S/30 and S/34 contained 106, 171, 215, 241, 346 and 412 g DM kg^-1, respectively. They contained 1.8, 104.2, 97.3, 77.4, 83.5 and 48.0 g lactic acid, 55.5, 34.6, 26.7, 24.0, 19.8 and 15.2 g acetic acid and 53.96, 4.81, 4.05, 11.37, 0.01 and 0.00 g butyric acid per kg DM, respectively. The proportions of ammonia N in S/0, S/0 MK, S/6, S/10, S/30 and S/34 were 552, 195, 211, 212, 108 and 69 g kg^-1 total N, respectively. Both wilting and formic acid treatment improved stability of silage. The proportion of ammonia N and the concentration of acetic acid were negatively related to DM concentration (r = –0.84 and –0.89, P < 0.05). Both wilting and formic acid treatment improved the stability of silage. The concentration of NEL was markedly lower in S/0 (3.62 MJ kg^-1 DM) than in wilted (from 5.01 to 5.39 MJ kg ^-1 DM) and formic acid treated (5.22 MJ kg ^-1 DM) silages. Concentration of NEL was negatively related to the proportion of ammonia N (r = –0.98, P < 0.001), the concentration of acetic (r = –0.91, P < 0.05), propionic (r = –0.98, P < 0.001) and butyric acid (r = –0.99, P < 0.001). The results of the current study suggest that well fermented wilted grass silages can be stored in air tight silos for a period of more than ten years without taking a risk of being spoiled. In direct cut silage, lactic acid was degraded and silage got spoiled. Long term stability of unwilted silage can be improved by the formic acid treatment.