Seasonal Influence on Rumen Microbiota, Rumen Fermentation, and Enteric Methane Emissions of Holstein and Jersey Steers under the Same Total Mixed Ration

SIMPLE SUMMARY: The rumen microbiome plays a significant role in the breakdown of dietary substrates in the rumen and thus provides essential nutrients to the animals. However, methane (CH(4)) production by methanogens drains dietary energy. Therefore, manipulation of the rumen microbiome is one way to improve animal performance and reduce enteric methane emissions from ruminants. However, most previous studies have focused on dairy cattle at specific time points; thus, little is known about the rumen microbiome of steers and seasonal effects. This study aimed to compare the rumen microbiome, rumen fermentation and enteric CH(4) emissions of Holstein and Jersey steers over different seasons. Both season and breed affected the rumen microbiome and rumen fermentation, while only breed affected enteric CH(4) emissions. Our results suggest that both season and breed must be considered when manipulating the rumen microbiome to enhance animal performance. In addition, breed should be taken into consideration to reduce CH(4) emissions from steers. ABSTRACT: Seasonal effects on rumen microbiome and enteric methane (CH(4)) emissions are poorly documented. In this study, 6 Holstein and 6 Jersey steers were fed the same total mixed ration diet during winter, spring, and summer seasons under a 2 × 3 factorial arrangement for 30 days per season. The dry matter intake (DMI), rumen fermentation characteristics, enteric CH(4) emissions and rumen microbiota were analyzed. Holstein had higher total DMI than Jersey steers regardless of season. However, Holstein steers had the lowest metabolic DMI during summer, while Jersey steers had the lowest total DMI during winter. Jersey steers had higher CH(4) yields and intensities than Holstein steers regardless of season. The pH was decreased, while ammonia nitrogen concentration was increased in summer regardless of breed. Total volatile fatty acids concentration and propionate proportions were the highest in winter, while acetate and butyrate proportion were the highest in spring and in summer, respectively, regardless of breed. Moreover, Holstein steers produced a higher proportion of propionate, while Jersey steers produced a higher proportion of butyrate regardless of season. Metataxonomic analysis of rumen microbiota showed that operational taxonomic units and Chao 1 estimates were lower and highly unstable during summer, while winter had the lowest Shannon diversity. Beta diversity analysis suggested that the overall rumen microbiota was shifted according to seasonal changes in both breeds. In winter, the rumen microbiota was dominated by Carnobacterium jeotgali and Ruminococcus bromii, while in summer, Paludibacter propionicigenes was predominant. In Jersey steers, Capnocytophaga cynodegmi, Barnesiella viscericola and Flintibacter butyricus were predominant, whereas in Holstein steers, Succinivibrio dextrinosolvens and Gilliamella bombicola were predominant. Overall results suggest that seasonal changes alter rumen microbiota and fermentation characteristics of both breeds; however, CH(4) emissions from steers were significantly influenced by breeds, not by seasons.