Two experiments were conducted to evaluate the relationship between rumen liquid-associated bacterial community structures and post-weaning liveweight gain (LWG) of Brahman crossbred steers. Bacterial diversity was assessed using denaturant gradient gel electrophoresis (DGGE). In Experiment 1, 16 steers were selected from a group of 100 steers by pairing steers with the same weaning weight, but different LWG 90 days after weaning (n = 8 highest growth, 0.21 ± 0.01 kg/day; and n = 8 lowest growth –0.07 ± 0.01 kg/day). Thereafter, steers were allocated to a 28-day pen study and fed Mitchell grass (Astrebla spp.) hay to examine DM intake and digestibility, rumen parameters and rumen microbial community in these two groups. Rumen fluid samples were taken by stomach tube 3 h after feeding on the last day of the pen phase. In Experiment 2, 12 pairs of weaned steers were selected from a group of 203 steers on the same basis as Experiment 1. The post-weaning LWG were 0.20 ± 0.03 and 0.02 ± 0.03 kg/day for the 12 highest and 12 lowest growth animals selected, respectively. Steers then grazed dry season Sabi grass (Urochloa mosambicensis) dominant pasture for 21 days, before rumen sampling 3 h after morning grazing by stomach tubing on the last day. In Experiment 1, there were no significant differences between the two groups in DM intake, digestibility, ruminal pH, total volatile fatty acid (VFA) concentration or the VFA proportion. In Experiments 1 and 2, rumen ammonia-N concentration was similar between LWG groups and there was no evidence of a relationship between liquid-phase DGGE profiles of rumen bacteria and high or low post-weaning LWG using multivariate analyses. Furthermore, the number of detected DGGE bands, the Shannon–Wiener and evenness indexes were not different between LWG groups. This DGGE analysis of the most abundant groups of rumen fluid-associated bacteria suggests that microbial populations were not related with the differences observed in post-weaning LWG within a group of weaners fed low crude protein diets.
Differences between Betaproteobacterial Ammonia-Oxidizing Communities in Marine Sediments and Those in Overlying Water
