Effects of different feed additives on growth performance, carcass characteristics, and apparent total nutrient digestibility of finishing beef steers

The objective was to evaluate the effects of feed additives on intake, growth performance, apparent digestibility of nutrients, and ruminal fermentation characteristics of finishing beef cattle. In Experiment 1 (Exp. 1), fifty-six Angus-crossbred steers (initial body weight = 356 ± 26 kg) were assigned to a randomized complete block design with a 2 × 2 factorial arrangement of treatments, including (1) monensin sodium at 33 mg/kg dry matter (MON; [-] or [+]), and (2) a proprietary multi-component plant extract feed additive at 10 g/steer/day (PE; [-] or [+]) containing orange peel bitters, onion extract, specific fatty acids, and soybean and corn oil. This resulted in four treatment groups: CON (MON-/PE-), MON (MON+/PE-), PE (MON-/PE+), or MON + PE (MON+/PE+). The 168-day study included a 24-day adaptation and 144 days on a 90:10 concentrate-to-roughage finishing diet. In Experiment 2 (Exp. 2), eight ruminally cannulated steers were used in a duplicated 4 × 4 Latin Square design to evaluate the same treatments used in Exp. 1. No MON × PE interactions or main effect of MON and PE were observed for body weight or dry matter intake (DMI) in Exp. 1 (P ≥ 0.16). Steers fed PE+ (PE and MON + PE) had a greater average daily gain (2.37 kg/steer/day) during the adaptation period compared to steers fed PE- (CON and MON; 2.07 kg/steer/day; P = 0.04). Consequently, feed efficiency (GF) during the adaptation period was 9% greater for steers fed PE+ (P < 0.01). A tendency of MON × PE interaction was detected for GF from day 72 to 168 (P = 0.09), and steers MON + PE tended to have greater GF compared to MON (P = 0.06) but not compared to CON or PE (P ≥ 0.20). In Exp. 2, feeding MON+ (MON and MON + PE) tended to decrease DMI compared to steers fed MON- (CON and PE; P = 0.06). A MON × PE interaction was detected for ruminal concentration of propionate, butyrate, and isovalerate (P ≤ 0.02). Steers fed MON + PE and CON had a greater concentration of propionate compared to MON and PE (P ≥ 0.04). The ruminal concentration of butyrate was greater for steers fed PE + compared to steers fed PE- (P ≤ 0.001). Steers fed PE + had a lower acetate: propionate ratio compared to steers fed PE- (P = 0.04). Ruminal concentration of ammonia nitrogen was less for steers fed PE+ (P < 0.01). In summary, the feed additives evaluated had minimal effect on DMI. Feeding PE and MON + PE enhances growth performance during the initial days on feed and improves ruminal fermentation characteristics.