Evaluation of Intake Limiting Agents in a Self-fed Dried Distillers' Supplement

Response to range supplementation is in part driven by level of supplement consumed and amount of associated variation. In order to evaluate intake limiting agents in a self-fed dried distillers? grain supplement (DDG), heifers (n=59) in Trial 1 were offered an ad libitum amount of sorghum ? sudangrass hay as well as DDG containing either no limiter (CON), monensin (185 mg/kg; MON), or one of six additional limiters alone or in combination with monensin (185 mg/kg, +M). Evaluated treatments and initial rates consisted of sodium chloride (NACL, 10%), urea (UREA, 2%), sodium bicarbonate (LIME, 1.68%), DL-malic acid (MLAC, 3%), calcium propionate (CAPR, 3%), and sodium bicarbonate plus urea (LIUR, 1.68% + 2%). Supplement intake was recorded daily and limiters were evaluated over three rates of inclusion, each for a duration of 14 d, on the basis of intake level, intake variation (cumulative stability), and rate of intake change over time (temporal stability). Data was analyzed as a 7 ? 2 factorial initial 7 days of each period were removed to avoid acclimation influence. A baseline period was observed to ensure no inherent differences were detected. Within the initial rate period, limiter affected OM intake (P = 0.02) as consumption was reduced by NACL (P < 0.01) and tended to be lower when limited by MLAC (P = 0.14) and LIUR (P = 0.11). Neither monensin (P = 0.86) nor a limiter ? monensin interaction were present. Cumulative stability was indicated that heifers consuming NACL (P < 0.01) and CAPR (P < 0.01) consumed supplement with greater regularity than did CONT. Monensin (P = 0.75) and monensin ? limiter (P = 0.76) did not influence intake stability. Temporal stability was unaffected by limiter (P = 0.43), monensin (P = 0.69), or monensin ? limiter (P = 0.93). When rate of inclusion was 2 ? initial rate, intake was affected by limiter (P < 0.01) with observations similar to the initial period. No monensin (P = 0.49) or interaction (P = 0.27) effect was present. Cumulative stability was unaffected by limiter (P = 022), monensin (P = 0.39), or interaction (P = 0.86). Temporal stability was increased with monensin (P 0.05) and an interaction resulted in an increased rate of supplement intake change in CONT when monensin was included. When supplement included limiters at 4 ? the initial rate, Effects on intake and cumulative stability by limiter were the only significant responses. Intake of LIUR, NACL, and MLAC were reduced relative to CONT while NACL was consumed with greater regularity. Trial 2 was conducted to further compare sodium chloride and DL-malic acid as limiting agents. Each were included in a self-fed DDG supplement offered to steers (n=60, mean initial BW = 191 kg) at identical rates (8%, 16% 24%, and 32%) in addition to monensin (66 mg/kg). Within each rate, MLAC reduced supplement intake more effectively than NACL while cumulative stability and temporal stability measures were similar among limiter and only deviated from control levels at lower rates.