Step 4: Reading the Test — 



1. Between 66 and 78 hours after injection (72 hours is optimum), the original tester 

 (unless an alternative test reader has been authorized by the Area Veterinarian-in- 

 Charge [AVIC]) must determine the results of the test by both observation and 

 palpation of the injection site. 



2. Verify the identification of the restrained animal and raise the tail to exert slight 

 tension on the caudal fold. 



3. Visually inspect the injection site closely and palpate it carefully to detect changes 

 from the normal. Any swelling or increase in thickness of the skin is considered 

 to be a response to the tuberculin. If there is doubt about whether a response has 

 occurred, palpate the opposite side of the tail to determine if there is a change 

 from normal. Any observed change should be carefully considered and recorded. 



4. Test observation without palpation is unacceptable. 



Step 5: Recording the Results of the Test — 



1. Use VS Form 6-22. 



2. Enter "N" (negative) when you observe no change in the tissue at the site 

 of injection. 



3. Enter "S" (suspect) when you observe visual swelling or any palpable increase in 

 the thickness of the area surrounding the injection site. 



Reactions and Interpreting Test Results 



If an animal is exposed to the antigens present in bovine TB, a tuberculin injection 

 results in a delayed hypersensitivity reaction manifested by swelling and induration at 

 the injection site. A positive response usually begins within 8 to 12 hours and peaks 

 about 72 hours after injection. 



If the test produces any type of response, immediately notify^ your APHIS-VS Area 

 Office and State animal health officials. The caudal-fold test is used as a presumptive 

 diagnostic procedure, and animals classified as suspect must be evaluated further 

 by the comparative cervical (CC) test or sent directly to slaughter under permit. 

 Only Federal or State regulatory veterinarians who have had specialized training 

 may conduct a CC test. The CC test must be performed within 10 days of the initial 

 caudal-fold injection in cattle and bison, or the herd owner must wait 60 days 



2-S 



