154. Effects of Feed Additives on Intake, Growth Performance, and Health Responses of Receiving Feedlot Cattle.

Abstract The receiving period is a critical phase in beef production, often associated with reduced performance and increased incidence of bovine respiratory disease (BRD). The use of feed additives can improve cattle performance and support animal health during this period. This study evaluated the effects of feed additives on growth performance and health responses of feedlot heifers during a 63-d receiving period. Crossbred beef heifers (n = 336; initial body weight (BW) = 274 kg) were blocked by initial BW and allocated to 30 pens (10-13 heifers/pen; 10 pens/treatment; 112 heifers/treatment). Three feed additives were evaluated: 1) monensin sodium (MON) at 33 mg/kg dry matter (DM), 2) a proprietary multi-component plant extract (PE) feed additive containing orange peel bitters, onion extract, specific fatty acids, and soybean and corn oil at 1g/kg DM, or 3) the combination of MON+PE. The basal diet contained (DM basis) 40% ground wheat hay, 31% steam flaked corn, 6% dried distillery grains, 20% Sweet Bran, and 3% of a mineral-vitamin premix containing the feed additives. Heifers were fed once daily, and after feeding, were evaluated for signs of BRD using the DART scoring system (depression, anorexia, respiration, and temperature). Antimicrobial therapy was administered to heifers with DART scores 3 or 4 and a rectal temperature ≥ 40 °C. Growth performance (final BW, average daily gain (ADG), dry matter intake (DMI), and gain:feed ratio (G:F)) and health outcomes (BRD morbidity (% of heifers that received antimicrobial treatment) were evaluated. Blood samples were collected on day 63 to determine antibody titers against BRD pathogens. Data were analyzed using PROC MIXED and GLIMMIX in SAS with pen as the experimental unit. Differences were considered significant when P ≤ 0.05. No differences were detected for final BW (402, 397, 397 kg; P = 0.26), ADG (2.04, 1.95, 1.96 kg/d; P = 0.26), DMI (9.84, 9.93, 9.48 kg/d; P = 0.46), and G:F (0.207, 0.197, 0.208; P = 0.14), between MON, PE, MON+PE, respectively. Morbidity did not differ (P = 0.52) among treatments (14.9% (n = 17/112), 8.18% (n = 9/112), 14.3% (n = 16/112)) for MON, PE, and MON+PE, and antibody titers were also similar between treatments for bovine herpesvirus-1 (14.7, 27.3, and 15.4 log₂; P = 0.73), bovine viral diarrhea virus type 1A (432, 648, and 529 log₂; P = 0.35), bovine viral diarrhea virus type 2 (673, 787, and 537 log₂; P = 0.68), parainfluenza-3 virus (200, 191, and 213 log₂; P = 0.30), and bovine respiratory syncytial virus (20.9, 20.5, and 23.4 log₂; P = 0.99) for MON, PE, and MON+PE, respectively. Overall, supplementation with MON, PE, or MON+PE resulted in comparable growth performance and health responses in feedlot heifers during the 63-day receiving period.