Distribution of trenbolone residues in liver and various muscle groups of heifers that received multiple implants at the recommended site of application.

Twenty heifers which were each administered 3 or 4 implants containing trenbolone acetate were slaughtered at 30 days post-implantation. Liquid chromatographic analyses were conducted on muscle collected from the rump, loin, shoulder, and neck, and on the liver of each animal. Residues present in liver were primarily 17a-trenbolone, and the residues found in the various muscle samples were primarily 17β-trenbolone. The mean concentration of 17a-trenbolone in liver was 4.3 ± 2.3 ng/g; the mean concentration of 17p-trenbolone in muscle tissues was <0.4 ng/g. There was a small but statistically significant effect of the number of implants used on the mean concentration of residues in loin muscles; animals with 3 trenbolone implants had higher mean residue concentrations than animals with 4 trenbolone implants. This suggests that, though the impact of implant numbers on the mean concentration of residues in muscle tissues is negligible relative to currently generally accepted maximum residue levels, mechanisms may exist for selective distribution and retention of residues within different muscle groups.