166 Influence of Source of Metabolizable Protein and Implant Status on Feedlot Performance and Feeding Behavior in Yearling Steers

Abstract

Abstract Crossbred steers (n = 60; beginning BW 454 ± 24 kg) were used in a split-plot design with a 2 x 3 factorial arrangement of treatments to determine effects of source of metabolizable AA and implant status on animal performance and feeding behavior. Calves were blocked by initial BW and assigned to 1 of 5 BW blocks. Pen (n = 2 pens, 6 steer/pen) within each BW block were fed diets formulated to meet the RDP requirement of cattle and provide 150% and 152% the metabolizable Lys and Met requirement (RP-AA), or a diet designed to meet RDP and closely match the predicted metabolizable Lys and Met requirement (RDP-ONLY; metabolizable Lys = 99.3% of required; metabolizable Met = 119% of required, NASEM, 2016). Subsequently, within pen two calves were randomly assigned to 1 of 3 implant strategies: no implant, moderate (100 mg trenbolone acetate and 14 mg estradiol; Synovex Choice) or potent (200 mg trenbolone acetate and 28 mg estradiol; Synovex Plus). Cattle were fed for 125 days and feed intake and feeding behavior was determined using a semi-autonomous feed monitoring system (GrowSafe System Ltd). Data were analyzed using the MIXED procedure of SAS. There was a tendency for an interaction of source of metabolizable AA and implant status on dry matter intake; calves with a moderate implant consumed less feed when fed RP-AA while calves with a potent implant consumed greater amounts. Dry matter intake was not affected by metabolizable AA supply (P = 0.87) or implant status (P = 0.43). There was an interaction of source of metabolizable AA and implant status on ADG; implanted calves gained similar amount regardless of source of metabolizable AA, but non-implanted calves fed RP-AA gained 25% less compared with RDP-ONLY diet. Moderate and potent implants had greater ADG (P < 0.01) than non-implanted cattle. Overall, ADG was not affected by source of metabolizable AA (P=0.95). Feeding behavior was largely unaffected by source of metabolizable AA or implant status. Feed intake per meal, number of meals per day, meal duration and visit duration were not influenced by source of metabolizable AA or implant status (P ≥ 0.16). Number of visits per meal tended (P = 0.07) to be greater for RP-AA while feeding rate tended (P = 0.09) to be less. There was a significant interaction of source of metabolizable AA and implant status on feeding rate (P < 0.01) as non-implanted and potently implanted calves ate feed at a lesser rate when fed RP-AA but moderately implanted calves fed RP-AA ate feed at a greater rate compared with RDP-ONLY. These data demonstrate that metabolizable AA requirements of growing cattle are dynamically related to implant status in cattle, but that implant status does not largely influence feeding behavior.