Evaluation and Comparison of Four Screening Tests against Milk Culture for Detection of Subclinical Mastitis in Lactating Cattle and Buffalo in Egypt

Subclinical mastitis (SCM) is an asymptomatic worldwide udder infection that results in substantial losses to the dairy industry. Our main objective was to evaluate and compare the clinical performance of 4 commercially available screening tests for diagnosing SCM. Foremilk samples were collected from 428 quarters of 107 apparently healthy lactating cows and buffaloes from El-Menofia governorate from 2020 to 2022. Quarter somatic cell count (SCC) was estimated using the FOSS-BacSomatic® counter and the California Mastitis Test (CMT), with SCM defined as SCC > 200,000 cells/mL. Milk pH was measured cow-side using an AD11®pH-meter and BOVIVET® indicator paper. Bacterial cultures of foremilk samples were used to diagnose SCM as a reference method based on the isolation of the causative pathogens. The tests’ performance was evaluated by calculating test sensitivity (Se), specificity (Sp), and accuracy at the optimal-cut-point for each test. FOSS-BacSomatic® counter was the best-performing test for diagnosing SCM (Se = 0.967, Sp = 0.943, accuracy = 0.957) at an optimal-cut-point of >200,000 cells/mL. For comparison, CMT is the second best-performing test at an optimal-cut-point of a non-negative score (Se = 0.892, Sp = 0.878, accuracy = 0.887). The test performance of the AD11® pH-meter and BOVIVET® indicator paper was fair, however, the AD11® pH-meter performed better than the BOVIVET® indicator paper with Se = 0.807, Sp = 0.845, and accuracy = 0.822. We concluded that the FOSS-BacSomatic® counter and CMT are considered good tests for diagnosing SCM. On the other hand, milk pH doesn’t provide a clinically useful method for diagnosing SCM. However, based on cost, availability and analysis time, there doesn't seem to be a persuasive reason to select the FOSS-BacSomatic® counter over the traditional CMT to diagnose SCM.