Effects of Storage Time and Temperature on the Fermentation Characteristics of Rumen Fluid from a High-Forage Diet

The objective of this experiment was to investigate the effects of storage temperature and preservation time on the fermentation characteristics of rumen fluid collected from six Hu sheep fed a high-forage diet. The storage temperatures were set at −80 °C and −20 °C, and the preservation times were labelled as follows: 0 d (fresh rumen fluid, D0), 7 d (D7), 14 d (D14), 30 d (D30), 60 d (D60), 120 d (D120), and 240 d (D240). A repeated-measures design was applied to analyze the fermentation characteristics of rumen fluid across each preservation time point and storage temperature. The results showed that storage temperature had no significant effects on pH value, ammonia nitrogen (NH3-N), microbial protein (MCP), and volatile fatty acid (VFA) concentration and proportion (p > 0.05). Specifically, the pH value increased on D7, D14, and D60 (p < 0.05), while the MCP concentration decreased on D7, D14, D30, D120, and D240 but increased on D60 (p < 0.05), and the concentration of NH3-N decreased on D14 (p < 0.05). The acetate concentration increased on D30, while the concentrations of propionate, butyrate, valerate, and total VFA increased on D60 (p < 0.05). The concentration of isovalerate decreased on D60, and isobutyrate and branched-chain VFA concentrations decreased on D120 (p < 0.05). The proportion of acetate increased on D30, while the butyrate and valerate proportions increased on D60, and the proportions of isovalerate, isobutyrate, and branched-chain VFA decreased on D60 (p < 0.05). For rumen fluid from a high-forage diet, the storage temperature (−80 °C and −20 °C) did not affect its fermentation characteristics, suggesting that rumen fluid could be preserved at −80 °C or −20 °C without altering its fermentation characteristics. The fermentation parameters of rumen fluid changed significantly after 7 days of preservation; hence, it is recommended to finish determining the fermentation parameters of rumen fluid within 7 days of collection. The concentrations and proportions of most VFA changed after 30 days of preservation; therefore, it is recommended that VFA determination should be completed within 30 days of rumen fluid collection.