Methane category, immune response, feed efficiency, and rumen microbial community in lactating dairy cows

This study aimed to assess relationships of enteric methane (CH₄) yield (g/kg of DMI) with immune response, feed efficiency (ECM/DMI), and rumen microbiome in dairy cows, both in early and in late lactation. The DMI, BW, ECM yield, and CH₄ emission were measured in respiration chambers in early (n = 20, 32 ± 7 DIM) and nonpregnant late lactating (n = 14, 359 ± 90 DIM) multiparous Holstein cows. The in vitro immune response was studied in response to (1) LPS using whole blood, and (2) phytohemagglutinin and concanavalin A using peripheral blood mononuclear cells. The DNA was extracted from rumen content samples (esophageal tubing) for 16S rRNA microbial analysis. Cows were divided retrospectively into an equal number of cows with low (LMY) and high (HMY) CH₄ yield within each lactation group. In early lactation, CH₄ yields in LMY (n = 10) and HMY cows (n = 10) were (LSM) 18.7 and 25.3 g/kg of DMI, respectively. In late lactation, CH₄ yields in LMY (n = 7) and HMY cows (n = 7) were 22.8 and 26.8 g/kg of DMI, respectively. Statistical analysis was performed separately for each lactation group. In early lactation, we found that whole blood and isolated peripheral blood mononuclear cells from LMY compared with HMY animals were less responsive to stimulants in vitro. In addition, feed conversion efficiency was lower in LMY than HMY cows, and the relative abundance of the archaeal genus Methanosphaera and the bacterial genus Marvinbryantia were higher. In late lactation, we observed no differences in immune response and feed conversion efficiency between LMY and HMY cows. Still, in LMY cows several bacterial genera including Prevotella 7, Ruminococcus gauvreauii group, and Shuttleworthia were enriched, whereas in HMY cows Methanobrevibacter, Veillonellaceae UCG-001, Succinivibrionaceae UCG-002, Rikenellaceae RC9, and CAG-352 were enriched. The results indicate that in early lactation the animals with low CH₄ yield reach energy balance faster, at the expense of an inadequate immune response. Meanwhile, increased CH₄ yield in early lactation may reflect higher rumen fermentation activity, fostering feed efficiency and energy availability for supporting immune function.