Supplementation of a Phytogenic Feed Additive on Growth Performance, Feed Intake and Carcass Traits of Growing and Finishing Beef Steers.

Phytogenic feed additives (PFA) have been shown to provide anti-inflammatory, anti-microbial and antioxidant properties across many species including livestock and can positively influence animal performance. The objective of this study was to evaluate the effects of feeding a PFA to growing and finishing beef steers on growth performance, feed efficiency, carcass traits, and liver abscesses. Forty-five crossbred steers (initial BW; 272 ± 20.5 kg) were housed in individual pens and used in a randomized complete block design including a 110-d growing period followed by a 120-d finishing period. The steers were blocked by BW and randomly allocated to 1 of 3 treatments: control (CON) basal diet without PFA or monensin; basal diet with a phytogenic feed additive (PFA; 500 mg· animal-1·/day-1) or basal diet with monensin (MON; 300 mg/head/d). The growing diet consisted of 60% silage and 40% concentrate, while the finishing diet consisted of 10% silage and 90% of concentrate (DM basis). In the growing period, dry matter intake (DMI) did not differ; whereas, final BW (415 vs. 403 kg; P = 0.10) and average daily gain (1.31 vs. 1.20 kg/d; P = 0.12) was numerically greater with PFA than CON, respectively, with no difference from MON. Feed efficiency (gain:feed) in the growing period was greater (P = 0.04) with MON (173 g/kg) than PFA (161 g/kg) and CON (156 g/kg). In the finishing period, growth performance, feed efficiency, carcass traits did not differ among treatments; whereas, DMI was numerically less (P = 0.11) with PFA (10.2 kg/d) than CON (10.8 kg/d), but there was no difference between PFA and MON (9.8 kg/d). The percentage of abscessed livers did not differ between PFA and CON, but the proportion of abscessed livers tended (P = 0.09) to be greater with MON compared with PFA and CON, without difference in severely abscessed livers among treatments. These results indicate that feed efficiency of growing steers was not improved by PFA to the level with MON. However, supplementation of PFA or MON resulted in similar finishing performance and feed efficiency. [ABSTRACT FROM AUTHOR]