Herd composite somatic cell counts: average linear score and weighted average somatic cell count score and milk...

Area of Science:

• Dairy Science
• Animal Health
• Mastitis Management

Background:

• Somatic cell count (SCC) is a key indicator of udder health in dairy cows.
• Linear score (LS) is a logarithmic transformation of SCC, often used for statistical analysis.
• Understanding the relationship between herd-level SCC and LS is crucial for accurate herd health assessment.

Purpose of the Study:

• To investigate the relationship between herd production weighted average somatic cell count (WASC) and average linear score (ALS).
• To evaluate different models for predicting WASC from ALS.
• To assess the implications of using regression models for converting ALS to WASC for herd management decisions.

Main Methods:

• Three regression models were employed to analyze the relationship between WASC and ALS.
• Model performance was evaluated using R-squared (R2) values.
• The best-fit model was used to explore conversion methods from ALS to WASC.

Main Results:

• The highest R2 was achieved with a model predicting log WASC from ALS.
• Converting ALS to WASC using regression models resulted in bulk tank SCC estimates approximately double those from individual cow basis conversions.
• A 1-unit increase in ALS was associated with a decrease of 190 kg in rolling herd average milk production.

Conclusions:

• The relationship between WASC and ALS is best described by a logarithmic model.
• Caution is advised when converting ALS to WASC using regression models to avoid overestimation of herd SCC.
• Elevated ALS is linked to reduced milk yield, highlighting its impact on dairy herd productivity.