Investigation of the rumen microbial composition in 16 week-old Holstein Friesian and Belgian Blue calves fed corn silage at different inclusion ages.

A randomized controlled trial was performed to assess the impact of CS inclusion time in HF and BB calves on calf performance and rumen function. Seventy five newborn HF calves were randomly assigned to 3 treatments: CS included in the pre- (4w), weaning (10w) or postweaning period (16w). Forty BB calves were
randomly appointed to: CS included in the pre- (6w) or postweaning period (16w). In HF, inclusion time of CS did not influence calf performance. In BB, inclusion of CS from the preweaning period decreased DMI compared
to calves receiving CS after weaning (1.66 kgDM/d vs 1.86 kgDM/d, respectively, Prumen fluid microbial composition was examined by performing 16s rRNA amplicon sequencing. NMDS-analysis showed a separate clustering according to CS inclusion time (pand BB a trend to shift from Prevotellaceae and Lachnospiraceae to Succinivibrionaceae, Ruminococcaceae and unidentified families as an adaptation for starch degradation. Rumen samples of HF showed a higher
microbial richness than samples of BB calves (p=0.01), explained by differences in 8 low abundant genera (prumen fluid microbial composition in order to digest CS. The lower ADG in BB could only be explained by the lower DMI capacity of BB and not by interbreed differences in microbial composition.