Milk production and somatic cell counts: a cow-level analysis.

Area of Science:

• Animal Science
• Dairy Science
• Veterinary Epidemiology

Background:

• Mastitis is a major concern in dairy herds, leading to significant milk loss and economic impact.
• Quantifying milk loss due to mastitis at the cow level is crucial for effective herd management.

Purpose of the Study:

• To quantify the relationship between 24-hour milk loss and total lactation milk loss caused by mastitis.
• To identify risk factors, including parity and milk production level, influencing mastitis-related milk loss.

Main Methods:

• Utilized individual cow test-day production records from 2,835 Ontario dairy herds.
• Employed a two-stage modeling approach using linear regression and mixed models to estimate milk loss based on somatic cell count (SCC), days in milk, parity, and milk quartile.
• Calculated 24-hour and lactation milk loss by comparing to a referent healthy animal (SCC ≤ 100 ×10(3) cells/mL).

Main Results:

• Somatic cell count (SCC) significantly impacted 24-hour milk loss, with losses increasing across parity and milk quartile (MQ).
• First-parity animals in the lowest MQ experienced 45% less milk loss compared to later-parity animals.
• Lactation milk loss ranged from 165 to 919 kg as average SCC increased, and was significantly influenced by the number of test days with SCC > 100 ×10(3) cells/mL.

Conclusions:

• Milk production level is a significant risk factor for milk loss due to mastitis.
• Dairy cows in higher milk quartiles and later parities experience greater milk losses from mastitis.
• Effective mastitis management strategies should consider parity and milk production levels to minimize economic losses.