Plasma Metabolites, Productive Performance and Rumen Volatile Fatty Acid Profiles of Northern Australian Steers Supplemented with and Lucerne.

The hypothesis tested was that tropical steers supplemented with the legume and lucerne, a widely characterized temperate legume of high nutritive value, would elicit similar responses in plasma metabolite profiles, productive performance, nitrogen retention, and volatile fatty acids (VFA). The tannin-binding compound, polyethylene glycol-4000 (PEG), was added to the diets (160 g/kg dry matter) with the objective of further exploring nitrogen (N) utilization in the animals supplemented with relative to lucerne. From February to June 2020, sixteen yearling Brangus steers (average liveweight of 232 ± 6 kg) were fed a background diet of Rhodes grass () hay for 28 days, before introducing three cultivars ( cv. JCU2, cv. JCU4, cv. JCU7) and lucerne () at 30% dry matter intake (DMI). Relative to the backgrounding period, all supplemented steers exhibited similar growth performance. Steers supplemented with recorded a lower DMI and animal growth performance, but higher fecal N concentration than animals supplemented with lucerne. Among the three cultivars, there were no significant differences in N concentrations, VFA, and plasma metabolite profiles. The addition of PEG induced higher rumen iso-acid concentrations and fecal N excretion. However, feeding spp. to tropical steers could be a valuable means of increasing N utilization, which is attributable to the presence of tannins, and, consequently, improve animal productive performance. Since supplementation with lucerne resulted in higher liveweight, daily liveweight gains, and overall animal performance than supplementing with , the tested hypothesis that both supplements will elicit similar animal performance does not hold and must be rejected. Further in vivo investigation is needed to better understand the impact of tannins in on N utilization.