Tetracycline Biomarker Analysis

Tetracycline is administered to an animal either by injection or in treated food. This results in the formation of a “biomarker” in tooth and bone that can be seen in thin, calcified sections viewed under a fluorescent microscope. The tissue reaction with tetracycline produces a clearly visible mark only during the season of most rapid growth. In late fall, winter, and early spring, cementum growth is much reduced and there may be no visible biomarker.

Pictured at left is a thin first premolar tooth section from a raccoon. Microscopic examination with ultraviolet light reveals the fluorescing layers induced by tetracycline.

Applications & Complications

Applications of this technique include animal identification, estimating black bear population size through “mark-recapture”, and evaluating the efficacy of vaccines or contraceptives by examining samples taken from animals in the treated area. The primary reason that attempts fail with biomarkers is inadequate dosage. In black bears, an old animal may not reveal a biomarker even if it received an adequate dose. The rate of cementum growth in old animals is reduced, and may not be enough to incorporate the amount of reactive material necessary for a clear mark. 


Administer an adequate dosage of tetracycline during the summer. The first premolar (PM1) in bears is an acceptable specimen for biomarker screening, but the third incisor (I3) and canine are larger and may have greater biomarker visibility. Please submit the full length of the tooth for analysis, as tetracycline cannot be detected in crowns. To compensate for the potentially inadequate biomarker induction in old bears, collect a segment of rib bone along with the tooth. The bone may contain a more clearly visible biomarker until 2-3 years after induction.

Effect of Tetracycline on Hair Samples

Seven hairs from Maine raccoons that tested positive and one hair from a specimen that tested negative were analyzed to detect the presence of tetracycline. The eight hairs were mounted on microscope slides, with care taken to include each root bulb. They were examined under a fluorescent microscope, using Matson’s standard analysis procedure.

The seven positive animals had recent biomarkers, formed within the previous 4-8 weeks. If tetracycline was incorporated at all into hair, fluorescence should have been observed because hair elements present in the specimens were being formed at the time of tetracycline ingestion. No part of any hair in any of the specimens showed tetracycline fluorescence, suggesting that tetracycline ingestion does not produce a visible fluorescent biomarker in hair.