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

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Abstract 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.

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