Weaning methods affect ruminal methanogenic archaea composition and diversity in Holstein calves

The objective of the present study was to examine the effect of different weaning methods on the ruminal methanogenic archaea composition and diversity in Holstein calves.Thirty-six newborn Holstein bull calves were assigned to 1 of 3 treatments:(1)conventional weaning(d 56)and fed a high proportion of solid feed(CWS);(2)conventional weaning(d 56)and fed a high proportion of liquid feed(CWL);(3)early weaning(d 42)and fed with a high proportion of solid feed(EWS).High-throughput sequencing of the methyl coenzyme M reductase(mcr A)gene,which encodes theα-subunit of methyl coenzyme M reductase-the enzyme that catalyzes the final step in methanogenesis was used to determine the composition and diversity of rumen methanogens.No significant difference(P>0.05)was observed for operational taxonomic units(OTUs)or richness indices,but diversity indices increased(P<0.05)for calves fed high dietary solids.Predominant families across the three treatments were Methanobacteriaceae,Thermoplasmataceae and Methanomassiliicoccaceae.Calves in the EWS treatment had a higher(P<0.05)relative abundance of Methanobrevibacter sp.strain AbM4 and Methanosphaera stadtmanae,while calves in the CWL treatment had a higher(P<0.05)abundance of Methanosphaera sp.strain SM9.A positive(P<0.05)relationship was identified between butyrate and Methanobrevibacter sp.strain AbM4.In conclusion,the composition and diversity of methanogens in the rumen of Holstein calves varied under the different weaning methods.This study identified a positive relationship between butyrate and Methanobrevibacter sp.strain AbM4,potentially reflecting correlations between ruminal fermentation variables and methanogenesis function.These in-depth analyses provide further understanding of weaning methods for intensified production systems.