08/10/2023
An important note when testing your herd:
“TRUST YOUR INTUITION!”
Disease testing is a great way to monitor your herd’s health. However, blood work is not 100% foolproof and has a margin of error in its reporting accuracy. Various blood panels are evaluated using ‘sensitivity’ and ‘specificity’ measures:
Sensitivity - A test’s ability to successfully identify an animal with disease as POSITIVE. A test with low sensitivity is more prone to providing FALSE NEGATIVES: indicating a diseased animal is healthy even when they aren’t. A high sensitivity allows us to confidently say a positive is truly positive.
Specificity - A test’s ability to successfully identify a healthy animal as NEGATIVE. A test with low specificity is more prone to providing FALSE POSITIVES: indicating a healthy animal has a disease even when they do not. A high specificity allows us to confidently say a negative is truly negative.
ELISA (enzyme-linked immunosorbent assay) is a common diagnostic method used in the detection of antibodies specific to caseous lymphadenitis. However, the test’s sensitivity and specifity are variable across testing facilities, testing methods, and even across herds. While the tool is excellent for broad monitoring of herd health, it cannot and should not replace hands-on palpation and observation of your stock at the individual level.
Despite my hopes that a second bout of testing would prove 142 CLA-free, palpation uncovered a supramammary abscess (suggesting a false negative result). Considering the evolving state of CLA control within the herd, the presence of an abscess in a lymph node region (although an uncommon presentation) led to the decision to terminally remove 142 from the herd.