Effects of Replacing Rice Straw with Corn Straw Silage Treated with Different Additives on Growth Performance, Blood Parameters, and Rumen Microorganisms of Fattening Cattle

This experiment aimed to evaluate the impact of various feed additive-treated silage corn straw on the growth performance, blood parameters, nutrient apparent digestibility, and rumen fermentation in Simmental cattle. Eighteen healthy Simmental bulls (275.64 ± 15.27 kg) were randomly assigned to three groups, each consisting of six bulls: a control group (CON) receiving a basal diet, an experimental group, (OS) wherein 20% of the rice straw in the control group’s diet was substituted with silage corn straw treated with organic acid, and another experimental group (MS) wherein 20% of the rice straw was replaced with silage corn straw mixed with corn flour, lactic acid bacteria, and organic acid. All cattle were fed at 08:30 and 16:30, twice each day, with unrestricted access to water throughout the study. The results indicated that silage had no effect on the growth and serum biochemical indexes of beef cattle among all groups. However, other parameters, mainly rumen fermentation parameters, nutrient digestibility, and rumen microorganisms, were affected by the silage. The MS group significantly increased the concentration of microbial protein (MCP) in the rumen of cattle compared to the CON group. The OS and MS groups had a similar apparent digestibility of ether extract and acid detergent fiber (ADF), but a higher digestibility of dry matter (DM) (p = 0.001) and crude protein (CP) (p < 0.001) compared to the CON group. The rumen bacterial community of the MS group had a lower abundance of Proteobacteria than the CON group (p = 0.016). The abundance of Firmicutes in the MS group was not significantly different from the CON group, but there was an increasing trend compared with the OS group (p = 0.054). A Spearman correlation analysis showed that the apparent digestibility of NDF and CP was negatively correlated with Succinivibrionaceae UCG-002 (r = −0.552, p = 0.018; r = −0.668, p = 0.002), Succinimonas (r = −0.774, p < 0.001; r = −0.513, p = 0.029), and Ruminobacter (r = −0.583, p = 0.011; r = −0.618, p = 0.006). The apparent digestibility of DM exhibited a negative correlation with Succinivibrionaceae UCG-002 (r = −0.538, p = 0.021) and Succinimonas (r = −0.642, p = 0.004). Overall, corn straw silage with mixed additives has more feeding value, which can improve rumen fermentation and regulate the rumen bacterial community. Straw silage can change the rumen microbial community structure to improve the apparent digestibility of nutrients.