A lactation measure of somatic cell count.

Area of Science:

• Animal Science
• Dairy Science
• Veterinary Epidemiology

Background:

• Somatic cell count (SCC) is a key indicator of bovine udder health and milk quality.
• Accurate lactation-level SCC measures are crucial for dairy herd management and disease monitoring.
• Existing methods for combining sample day SCC data may not fully capture lactation dynamics.

Purpose of the Study:

• To develop and validate adjustments and weightings for combining individual sample day SCC into a comprehensive lactation measure.
• To investigate the influence of lactation stage and season on SCC in Holstein cows.
• To establish a robust method for assessing udder health across an entire lactation period.

Main Methods:

• Utilized 182,446 Holstein lactation records from 1984, including 1,660,782 sample day SCC (log base 2 scores).
• Analyzed SCC data stratified by average lactation score, lactation stage, and season.
• Developed weighting factors based on correlations between adjusted sample day scores and overall lactation averages.

Main Results:

• Stage of lactation effects on SCC were consistent for lower average scores (<3.5) but varied for higher scores (>4.5).
• Seasonality showed minor effects, with lowest SCC in winter (February-March) and highest in late summer/early autumn (August-October).
• First-parity cows exhibited less increase in late lactation SCC compared to subsequent parities.

Conclusions:

• The developed adjustments and weightings provide a more accurate lactation SCC measure for Holstein dairy cows.
• Understanding lactation stage and seasonal variations in SCC aids in precise udder health assessment.
• This methodology can enhance dairy herd management strategies by providing reliable lactation-level SCC data.