Influence of Lasalocid Level on Forage Intake, Digestibility, Ruminal Fermentation, Liquid Flow and Performance of Beef Cattle Grazing Winter Range1

Three experiments were conducted to study the effects of lasalocid level on performance, intake, digestibility, ruminal fermentation and fluid flow of beef cattle grazing dormant, tallgrass prairie. In Exp. 1, 120 pregnant, mature beef cows of primarily Hereford breeding (avg wt = 471 kg) were randomly assigned to received 0, 100, 200 or 300 mg lasalocid•head−1• d−1in 1.82 kg supplement. Weight changes at 30, 60 or 90 d, condition score change and calf birth weight were not affected (P>.10) by lasalocid level. In Exp. 2, estimates of intake and digestibility were obtained with 40 pregnant, mature Hereford cows (avg wt = 474 kg) and 12 esophageal-cannulated, Hereford × Angus steers (avg wt = 225 kg), using Yb and indigestible acid detergent fiber as markers for fecal output and digestibility, respectively. Levels of lasalocid provided to cows and steers were similar, on a body weight (BW) basis, to those in Exp. 1 and corresponded to approximately 0, .22, .44 or .66 mg lasalocid/kg BW. Total diet and forage organic matter digestibility for beef cows decreased (P<.01) at the .22 mg/kg BW level, but increased at the .44 and .66 mg/kg BW levels. Organic matter intake was not influenced (P>.10) by lasalocid addition. In Exp. 3, 16 ruminal-cannulated, Hereford × Angus steers (avg wt = 227 kg) were given the same lasalocid dosages per kg BW as in Exp. 2, and were used to study the effects of lasalocid on ruminal fermentation and fluid flow characteristics. Lasalocid did not influence (P>.10) ruminal pH, ammonia N, total volatile fatty acid (VFA) concentrations, molar proportions of individual VFA or fluid flow measurements. In conclusion, providing lasalocid in a range supplement to pregnant beef cows grazing poor-quality winter forage did not significantly alter performance; in addition, lasalocid did not significantly improve forage utilization characteristics in steers grazing similar pasture.