This study included 190 lactating cows from eight dairy farms and was
designed to investigate the sensitivity and specificity of a milk test
(Ketolac) for detecting subclinical ketosis in dairy cattle. Blood an
d milk samples were collected between 38 and 50 days post partum, At a
beta-hydroxybutyric acid concentration in blood of 1.2 mmol/L, the pr
evalence of ketosis was 14%. A Response Operator Characteristic curve
was drawn for two milk test values: 100 mu mol/L and 200 mu mol/L, Ass
essment of several beta-hydroxybutyric acid cut-off values in blood sh
owed that when 100 mu mol/L on the Ketolac milk test was defined posit
ive, the most desirable sensitivity-specificity combination was achiev
ed. This milk test can be routinely used to screen a herd for subclini
cal ketosis.