Effects of Different Feed Additives on Intake, Nutrient Digestibility, and Ruminal Fermentation Characteristics of Finishing Beef Cattle

Abstract Feed additives such as ionophores and plant-based compounds have been widely studied in ruminant nutrition for their ability to modulate ruminal fermentation and influence dry matter intake (DMI), with the goal of improving feed efficiency and animal health. Nevertheless, the combined use of these additives still warrants further investigation regarding their effects on nutrient digestibility and ruminal fermentation, especially given the wide variety of commercially available products that differ in composition and mode of action. The objective of this experiment was to evaluate the effects of feed additives and their combinations on DMI, apparent total tract nutrient digestibility, ruminal fermentation characteristics, and rumination time of finishing beef steers. Eight ruminally cannulated steers (average BW = 404 ± 44 kg) were used in a duplicated 4 × 4 Latin square design to evaluate the effects of four treatments: Control (CON): no feed additive in the basal finishing diet; Monensin (MON): dietary supplementation of sodium monensin at 33 mg/kg of dry matter (DM basis; Rumensin 90, Elanco Animal Health); CattIActive (CA): dietary supplementation with CattIActive (a proprietary multi-component feed additive containing orange peel bitters, onion extract, specific fatty acids, and soybean and corn oil; Pro Earth Animal Health) at 10g/head/day; and Monensin + CattlActive (MON+CA): combination of sodium monensin (33 mg/kg of dry matter) + CattIActive (10 g/head/day). Steers were fed a finishing diet containing 10% roughage and 90% concentrate once daily. Each 16-day experimental period included 10 days of adaptation to the experimental diets and 6 days of sample collection. Data were analyzed using the MIXED procedure of SAS. DMI tended to be less (P = 0.09) for steers fed MON compared to CON. No other effects were observed on nutrient intake or apparent total tract nutrient digestibility (P ≥ 0.18). Treatments did not affect ruminal pH (P ≥ 0.11). Ruminal proportion of acetate (C2) was less in steers fed CA and CA+MON compared to CON (P ≤ 0.03). Ruminal proportion of propionate (C3) was greater in steers fed CON and MON+CA compared to MON and CA (P ≤ 0.05), and C2:C3 ratio was less for MON+CA compared to MON (P = 0.02). Ruminal proportion of butyric acid was greater for CA and CA+MON compared to MON and CON (P ≤ 0.05). Ruminal ammonia nitrogen was less for CA and MON+CA compared to CON and MON (P ≤ 0.01). Additionally, MON+CA increased rumination time (min/kg DMI; P = 0.02) compared to CON. In summary, these results suggest that CA and the combination of MON+CA may positively alter ruminal fermentation characteristics without affecting the intake and the apparent total tract nutrient digestibility in finishing steers.