Question

Which of the following is the direct reason for high somatic cell count in the lacteal secretion of cows suffering with mastitis

• A. Low milk production associated with drying off of udder
• B. Increased production/release of white blood corpuscles (WBC)
• C. Bacterial multiplication in the udder
• D. Lowering of blood supply to mammary gland

Hint:

Remember:
- Somatic cells in healthy milk \(\approx\) Epithelial cells + Macrophages.
- Somatic cells in mastitic milk \(\approx\) White blood cells, primarily neutrophils (PMNs), migrating from blood to fight infection.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Somatic cells are cells derived from the body of the animal, found in small numbers in normal milk.
The somatic cell count (SCC) is a widely accepted index used to monitor udder health and milk quality.
An elevated SCC is a hallmark indicator of mastitis, reflecting the animal's immune response to an infection.

Step 2: Detailed Explanation:
Let us analyze the physiological events that occur in the udder during mastitis:
- When pathogenic bacteria enter the teat canal and multiply within the mammary gland, they release toxins and damage the secretory epithelial cells.
- This tissue damage triggers an acute inflammatory response within the udder.
- In response to inflammatory signals (such as cytokines and chemokines), blood vessels in the mammary gland dilate, and capillary permeability increases.
- This physiological change allows a large number of immune cells, primarily polymorphonuclear neutrophils (PMN) and other white blood corpuscles (WBCs), to migrate from the bloodstream into the alveolar spaces of the udder to fight the bacterial infection.
- Consequently, these white blood cells are shed directly into the milk.
- In healthy milk, the SCC is typically below \(100,000\ \text{cells/mL}\), consisting mostly of epithelial cells and macrophages.
- During mastitis, the SCC can rise to over \(1,000,000\ \text{cells/mL}\), with neutrophils making up over 90% of the total count.
Therefore, the direct reason for the high somatic cell count is the migration and release of white blood corpuscles into the milk.
While bacterial multiplication is the trigger for the infection, it is the host's cellular immune response (releasing WBCs) that directly increases the somatic cell count.

Step 3: Final Answer:
The direct reason for a high somatic cell count in mastitic milk is the increased production and release of white blood corpuscles (WBCs).