Fat/protein ratio in first DHI test milk as test for displaced abomasum in dairy cows

First DHI test milk that was sampled prior to displaced abomasum (DA) diagnosis was used to evaluate milk fat/protein ratio (FPR) for prediction of subsequent DA in dairy cows. Odds ratio, sensitivity, specificity, predictive values, and likelihood ratio were determined. Twenty-seven DA cases were matched to three controls per case by herd and calving date. Milk was tested 18 to 23 days (95% CI) after calving, which was 9 to 17 days (95% CI) prior to DA diagnosis. Adjusted for parity and days in milk, a fat/protein ratio > or = 1.4 was 8.6 times more likely (95% CI, 2.8 to 26) to come from a cow subsequently diagnosed with DA than a fat/protein ratio < 1.4. Using the cut off value of 1.4, the sensitivity of the FPR for DA was 80% and the specificity was 69%. A response operating characteristics curve indicated that the minimum sum of false negative and false positive results was at an FPR cut off value of 1.4. The likelihood ratio indicated that fat/protein ratios > or = 1.6 are 3.3 times more likely to come from cows that are diagnosed subsequently with DA than from cows without DA. The fat/protein ratio in first DHI test milk might be useful as a test for subsequent DA in dairy cows.