Understanding the influence of sward type and dairy cow breed on enteric methane emissions through investigation of the rumen microbiome

The current study investigated the rumen microbiome of Holstein-Friesian (HF) and Holstein-Friesian × Jersey crossbred (JFX) dairy cows grazing three sward systems; a perennial ryegrass ( Lolium perenne ) monoculture receiving 250 kg nitrogen (N)/ha/year (PRG), perennial ryegrass with white clover receiving 125 kg N/ha/year (PRGWC), and a multispecies sward, consisting of grasses, clovers and herbs which also received 125 kg N/ha/year (MSS). Rumen fluid samples were collected at two time points, early-August and mid-October. Sward system had no effect on microbiome alpha or beta diversity. The bacterial genera Lachnospira and Prevotellaceae Ga6A1 group were both more abundant in PRGWC and MSS compared with PRG while Pseudoramibacter was more abundant in MSS compared with the other two sward systems. There was no difference in the total abundance of methanogenic archaea between swards (expressed as the ratio of archaea to bacteria) although the Methanosphaera genus was more abundant and the Methanobrevibacter genus was less abundant in PRGWC and MSS compared with PRG. The analysis also revealed a minor difference in microbiome beta diversity between the two dairy cow breeds, reflecting global microbiome configuration differences. Four specific bacterial genera were less abundant in JFX compared with HF. The JFX cows also had slightly greater Methanobrevibacter and slightly lower Methanosphaera abundance compared with the HF cows although total methanogen abundance was not different. The results from this study demonstrate that increasing sward species diversity has limited influence on the core rumen microbiome while crossbreeding HF with Jersey did have some influence. Both factors also altered the composition of the rumen methanogenic community. Further research is required to understand the relationship between these alterations and enteric methane emissions.