Fat/Protein Ratio in First DHI Test Milk as Test for Displaced Abomasum in Dairy Cows

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Abstract
First DHI rest milk that was sampled prior to displaced abomasum (DA) diagnosis was used to evaluate milk rat/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 rested 18 ro 23 days (95 % Cl) after calving, which was 9 to Iri days (95 % CI) prior to DX diagnosis. Adjusted for parity and days in milk, a fat/protein ratio greater than or equal to 1.4 was 8.6 times more likely (95% CI, 2.8 to 26) to come from a cow subsequently diagnosed with DX 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 far/protein ratios greater than or equal to 1.6 are 3.3 times more likely to come from cows that are diagnosed subsequently with DA than from cows without DX. The fat/protein ratio in first DHI test milk might be useful as a test for subsequent DA in dairy cows.