218
Evaluating two rates of monensin fed during the grain adaptation period on cattle performance and carcass characteristics
Performance and carcass characteristics were evaluated using two rates of monensin (Rumensin) during an 18-d grain adaptation period using 198 cross-bred steers (BW = 415 ± 17 kg). Monensin was supplemented at rates of either 360 (LOW) or 480 (HIGH) mg/steer daily. Cattle were adapted to increasing levels of dry-rolled corn and decreasing levels of wheat straw and corn silage. All diets contained the same basal diet of 10% wet distillers grains with solubles, 10% corn condensed distillers solubles, and 5% liquid supplement (DM basis). Urea and soybean meal were included in all diets to meet or exceed NRC requirements for MP. Steers were utilized in a randomized block design, blocked by BW, stratified by BW within block, and assigned randomly to pens. Pens were assigned randomly to treatments within blocks with 9 pens/treatment and 11 steers/pen. Interim performance was determined at d 25, after being on a common finishing diet for 7 d which provided 360 mg/steer of monensin daily. After the grain adaptation period, steers fed HIGH had lower (P < 0.01) interim BW compared with steers fed LOW. Dry matter intake was less (P = 0.01) when LOW was fed compared to HIGH. An improvement (P ≤ 0.02) was observed in ADG and G:F with the LOW rate of monensin during the 18-d adaptation period. However, no differences (P ≥ 0.17) were observed for DMI, ADG, or G:F during the subsequent 100-d feeding period. Additionally, HCW, marbling, 12th rib fat, LM area, calculated YG, dressing percent, and overall liver scores were not affected (P ≥ 0.18) by rate of monensin fed during adaptation. Steers fed the HIGH rate of monensin tended (P = 0.09) to have a lower percentage of “A” liver scores. This study suggests feeding the LOW versus HIGH rate of monensin during the adaption period has little to no effect on overall performance of the cattle. These data indicate that the LOW rate may be more advantageous with the steers being more efficient during the adaptation period. However, they do not maintain that efficiency through the entire finishing period.
Keywords: adaptation, additive, monensin