Impact of dietary crude protein concentrations in dairy cow diets on rumen microbiome, nitrogen use efficiency, and relationships with residual feed intake

Ninety dairy cows (30 cows per treatment) were randomly assigned to three dietary treatments:15%, 16% and 17% crude protein (CP) levels for 180 days. Rumen samples were collected at weeks 0, 4, 8, 12 and 20 post calving. Residual feed intake (RFI) was estimated for each cow during four 5-week periods (weeks 2-6, 6-10, 10-14 and 18-22 post calving), with these periods centered on the rumen sampling occasions at 4, 8, 12 and 20 weeks post calving. Cows from each treatment were ranked from high-RFI to low-RFI and six least efficient cows with high-RFI and six most efficient cows with low-RFI from each treatment (12 cows per treatment * 3 treatment* 5 time points = 180 smples) were selected for DNA extraction and sequenced via Illumina NovaSeq 6000 shotgun metagenome approach.