Calcium Propionate Supplementation Mitigated Adverse Effects of Incubation Temperature Shift on In Vitro Fermentation by Modulating Microbial Composition

Abstract

The ingestion of cold water in winter results in fluctuating decreases in rumen temperature, impacting rumen fermentation function and methane production. This study aimed to investigate the impact of calcium propionate (CaP) on rumen fermentation characteristics, methane production, and microbial microbiome under different in vitro incubation temperatures. A 2 × 2 factorial experiment was conducted over 72 h, with or without 2.5% CaP (dry matter [DM] basis) in substrate under a constant incubation temperature (39 °C, CIT) or shifting incubation temperatures (12 cycles in total, with each cycle consisting of 4 h of incubation at 39 °C followed by immediate transfer to 30 °C for 2 h, ITS). The results showed that ITS inhibited the gas production, methane production, and methane concentration at 12 and 72 h (p < 0.05), and reduced the concentration of ammonium nitrogen (−14.25%), propionate (−16.14%), butyrate (−12.67%), and total volatile fatty acid (−8.50%) at 72 h more than the CIT groups (p < 0.05). The addition of 2.5% CaP significantly increased the gas production at 72 h (+4.84%), asymptotic gas production (+5.08%, per 0.2 g DM substrate), concentration of propionate (+18.05%), and valerate (+9.45%) (p < 0.05) compared to CaP-free groups, while it had no observable effect on the production or concentration of methane. Furthermore, the addition of 2.5% CaP yielded a significant increase in the relative abundance of Bacteroides (p < 0.05). Under the ITS condition, the relative abundance of Methanomicrobiales decreased and was positively correlated with methane production at 72 h (r = 0.47, p < 0.05). Additionally, CaP decreased the abundance of Prevotella_UCG_003 (p < 0.05), which was negatively correlated with the asymptotic gas production (r = 0.45, p < 0.05). Overall, our study suggests that the addition of 2.5% CaP can alleviate the adverse effects of ITS on in vitro fermentation parameters by regulating microbial composition and sustaining a reduction in methane production.