Relationship between somatic cell counts and subclinical mastitis in lactating dairy cows

Area of Science:

• Veterinary Medicine
• Animal Health
• Dairy Science

Background:

• Subclinical mastitis (SCM) is a prevalent dairy cow disease impacting milk quality.
• Somatic cell count (SCC) is a key indicator for SCM, but its diagnostic threshold requires careful determination.
• Accurate SCM diagnosis is vital for herd health management and economic productivity in dairy farming.

Purpose of the Study:

• To establish an appropriate cow-level somatic cell count (SCC) threshold for differentiating subclinical mastitis (SCM) from normal milk in dairy cows in Bangladesh.
• To evaluate the sensitivity and specificity of various SCC thresholds using bacterial culture as the gold standard.

Main Methods:

• Bacterial culture was employed as the gold standard for diagnosing intramammary infection (IMI).
• Sensitivity (Se) and specificity (Sp) were calculated for different SCC thresholds (ranging from 100 to 300 × 10³ cells/mL).
• Three distinct definitions of IMI were established based on the involved pathogens to assess threshold performance under varying conditions.

Main Results:

• The sensitivity and specificity of SCC thresholds varied significantly depending on the definition of IMI used.
• Higher SCC thresholds (e.g., 300 × 10³ cells/mL) generally yielded lower sensitivity (ranging from 60.6% to 20.3%) but higher specificity.
• A lower SCC threshold of 100 × 10³ cells/mL demonstrated the highest sensitivity, minimizing false-negative results, while specificity increased with higher thresholds.

Conclusions:

• The cow-level SCC threshold of 100 × 10³ cells/mL is identified as appropriate for detecting subclinical intramammary infections in dairy cows.
• This threshold provides a balance between sensitivity and specificity for effective SCM diagnosis in the studied population.
• The findings support the use of a 100 × 10³ cells/mL SCC threshold for routine SCM screening in Bangladesh dairy herds.