Rumen microbiome populations and methane production in adult male and female sheep

Introduction Methane emissions from enteric fermentation in the rumen are a major contributor to the environmental footprint of ruminant livestock farming. Many factors regulate the rumen microbiome and methane production but how the rumen microbiome and methane production differs between males and females after sexual maturation, and the potential influence of steroid hormones, is not well understood. Methods We used restriction enzyme-reduced representation sequencing to determine rumen microbiome compositions from adult male and female sheep and portable accumulation chambers to measure their methane emissions. Additionally, we examined if steroid hormones had a direct effect on methane emissions from rumen fluid using an in vitro system. Results Overall, the rumen microbiome differed between male and female sheep, with differences (Bonferroni–Holm Adjusted P -value < 0.05) in abundance of 29 genera. Most of these differentially abundant microbes had small populations (<1% of the total), with Butyrivibrio (1.2%) and RUG740 (1.5%) the only two differentially abundant genera above 1%. However, based on testosterone or progesterone concentration classification of the animals within sex, no genera were differentially abundant, and sparse Partial Least Squares Discriminant Analysis showed no evidence of microbiome separation based on steroid hormone concentration classifications. No differences ( P ≥ 0.15) were observed in methane production between adult male and female sheep. Furthermore, androstenedione, testosterone, progesterone or estradiol did not directly affect ( P > 0.15) methane production in an in vitro rumen culture system. Discussion The microbiome differed between male and female sheep, but neither testosterone nor progesterone concentration classifications appeared influential in determining microbiome composition. Adult male and female sheep produced similar amounts of methane per day, with little evidence that differences in sex steroid hormones affected methane production. It seems likely that male and female ruminants will respond to products to reduce methane similarly. This suggests breeding programs for low-methane ruminants can regard male and female animals similarly, which would simplify genetic evaluation process and provide more flexibility around phenotyping.