In Korea, the agricultural industry has witnessed a growing emphasis on reducing reliance on imported forage by adopting locally available alternatives to enhance sustainability and self-sufficiency. Given the limited information on the potential use of whole-crop rice silage (WCRS) as livestock feed, this study evaluated the effects of total mixed rations (TMR) containing WCRS on the rumen microbiota of Hanwoo heifers. Thirty heifers (body weight = 351 ± 39 kg) were randomly assigned to three TMR diet groups for the early fattening period: oat hay (OH), oat hay with Italian ryegrass silage and corn silage (OIC), and silages from whole-crop rice, Italian ryegrass, and corn (WCRSEF). During the late fattening period, the same heifers (569 ± 40 kg) were reassigned to three other treatment groups: perennial ryegrass (PRG), Italian ryegrass silage and alfalfa hay (IRGA), and silage containing whole-crop rice (WCRSLF). The effects of different feeding diets on the rumen microbial composition of Hanwoo heifers were investigated using high-throughput 16S rRNA gene sequencing. The analysis revealed similar microbial diversity among the treatments across both fattening periods. Bacteroidetes and Firmicutes were the most dominant phyla during early and late fattening periods. Moreover, during the early fattening period, heifers fed WCRS exhibited a higher ratio of Bacteroidetes to Firmicutes, whereas Firmicutes became more predominant in the late fattening period. Hungateiclostridium and Porphyromonas were identified as biomarkers (LDA score > | 2 |; p < 0.05) for the WCRSEF and WCRSLF groups, respectively. Furthermore, the microbial co-occurrence network highlighted different patterns (| r | = 0.85; p < 0.05) between the early and late fattening periods. The results provide significant insights into the effects of WCRS as a substitute for conventional forages such as oat hay, perennial ryegrass, alfalfa, and Italian ryegrass silage. The findings suggest that WCRS can modulate the rumen microbiome of Hanwoo heifers.

The commercial feed additive, native rumen microbes (RC), derived from a diverse microbial community isolated from the rumen of Hanwoo steers is being explored to enhance rumen fermentation and improve ruminant feed utilization. This study evaluated the impact of native rumen microbes supplementation on methane emissions, microbial diversity, and fermentation efficiency on in vitro assessment. Treatments were as follows: CON (basal diet, without RC); T1 (basal diet + 0.1% RC); T2 (basal diet + 0.2% RC). Rumen fermentation parameters, total gas, and methane production were assessed at 12, 24, and 48 h of incubations. The in vitro gas production was carried out using the Ankom RF Gas Production System. Supplementation of RC significantly reduced the total gas production at 12, 24, and 48 hours of incubation (p < 0.05). Volatile fatty acid concentrations were increased, while acetate and propionate were decreased (p < 0.05) at 48 h by the supplementation of RC. Notably, the 0.1% inclusion level of RC significantly reduced methane production by 28.30% and 21.21% at 12 and 24 hours. Furthermore, microbial diversity analysis revealed significant shifts (p < 0.05) in bacterial composition between the control and treatment groups, while supplementation also promoted the growth of bacterial populations, such as Succiniclasticum. These findings suggest that native rumen microbes supplementation, particularly at 0.1% inclusion level, can enhance rumen microbial composition while significantly reducing methane production in vitro.