INFLUENCE OF INCREMENTAL ZERANOL IMPLANT DOSES ON THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF 3RD METACARPAL BONE AND CHEMICAL-COMPOSITIONOF LIVER AND SOFT-TISSUE FROM FEEDLOT STEERS

Chemical and physical characteristics of third metacarpal bones and li ver and rib soft tissue composition from feedlot steers were determine d. Steers were selected (32 from each experimental location) to repres ent the range in slaughter weight and composition for each treatment g roup in three (total. n = 1,088) feedlot experiments. Steers were impl anted with 0, 24, 36, 48, 60, 72, 84, or 96 mg of zeranol at approxima tely 140 d before slaughter. Cattle at each location were fed for the same number of days and slaughtered as a group. Zeranol dose had no ef fect on the chemical composition of bone, liver, or rib soft tissue wi th the following exceptions: zeranol decreased (P < .01) bone Ca conce ntration and increased (P < .07) liver P concentration. Zeranol implan tation decreased medullary cavity anterioposterior (AP) diameters and AP, cortical width (P < .08). Loads withstood by the bones up to flexu re (P < .08) and the strain at flexure (P < .09) were inversely relate d to the quadratic of zeranol dose. However, modulus of elasticity at flexure and breaking increased numerically with zeranol dose. Stress w ithstood by bones at flexure was greater (P < .09) for implanted steer s. Strain data indicate that metacarpals from steers receiving zeranol would exhibit less deformation upon loading to flexure (P < .09) than controls. These data indicate that administration of intermediate dos es of zeranol altered bone deposition of Ca, which resulted in modifie d third metacarpal physical and mechanical characteristics.