Natural feed additives in high-concentrate diets fed to Angus × Nellore finishing steers

Abstract

The study objective was to evaluate the use of naturally sourced feed additives to replace monensin in a high-concentrate diet on performance, behavior, and carcass characteristics. Eighty F1 Angus × Nellore steers [392 ± 2.6 kg of initial body weight (BW)] were assigned to 1 of 4 treatments: (1) monensin (29.5 mg/kg DM), (2) active yeast (85.0 mg/kg DM), (3) monensin and active yeast combined (at the same doses as above), and (4) a blend of essential oils (33.6 mg/kg DM). The basal diet (BD) had a roughage: concentrate ratio of 6:94. Sugarcane silage was used as roughage. The steers spent approximately 520 min resting (72 % of the daytime period), approximately 130 min eating (18 % of the daytime period), and 61 min ruminating (8.5 % of the daytime period). No difference was observed for dry matter (DM) intake during the adaptation phase (P > 0.05). Steers receiving yeast had the lowest average daily gain (ADG) in the adaptation phase (P < 0.05), however, this lower ADG did not have an impact on the final BW (P > 0.05). On the other hand, steers receiving essential oils presented a ADG 26.5 % lower than the others during the experimental phase (P < 0.05), which led to 18.3 kg lower (P < 0.05) final BW of these steers (P < 0.05). Differences in rib eye area and subcutaneous fat thickness can be attributed to the differences in the final BW and it is possible to infer that all the steers were at the same point of body development. We conclude that monensin can be replaced by active dry yeast in high-concentrate diets without compromising growth. Still, due a "lag time" for adequate rumen colonization of the yeast, steers-fed essential oils performed better during the adaptation phase. Then, essential oils (or other natural antimicrobial additives) combined with yeast are an option for adapting, which should be evaluated in future experiments.