Rumen Microbial Populations Associated with Feed Efficiency in Lambs Fed an Antibiotic Supplemented Forage Diet

The rumen microbial population is critical to the conversion of feedstuffs into volatile fatty acids for energy use by the host. Therefore, certain microbial species may play a key role in the efficiency of feed utilization. Our objective was to determine the association of feed efficiency classification with rumen microbial profiles in growing lambs. Targhee ewes (n = 80; initial BW = 58.84 ± 10.8 kg) were fed a forage-based diet treated with chlortetracycline and individual intake data were collected for 70 d using a GrowSafe System. From this, residual feed intake (RFI) was calculated as the difference between actual and expected feed intake. Ewes were ranked on RFI, and DNA was extracted from rumen fluid samples collected from the 10% most efficient (n = 8; Low RFI) and 10% least efficient (n = 8; High RFI) ewes. DNA samples were sequenced, and resulting paired-end reads were filtered, quality trimmed, and compared with a database of known 16S rRNA genes. Operational taxonomic units (OTU) were defined as sequence clusters with ≥ 97% identity. In total 320 prokaryotic OTU were present in at least one lamb. There were 33 OTU affected (P ≤ 0.05) by RFI class; 18 were of greater (P ≤ 0.05) abundance in low efficiency ewes and 15 were of greater (P ≤ 0.05) abundance in high efficiency ewes. Our results suggest that certain rumen microbial species may contribute to the observed variation in feed efficiency in ruminants provided an antibiotic supplemented diet.