Why is the CV from vaccination better in eye drop than in spray?

1. Accuracy in the dose received

In the eye drop method, each bird receives exactly one specific dose of vaccine (e.g. 0.03 or 0.05 ml).

✅ Therefore:

All birds receive the same amount of live virus.

The immune response in the flock is more uniform.

→ As a result, the SD (standard deviation) decreases ⇒ lower CV

In contrast, in the spray method:

Each bird inhales a different amount of vaccine droplets.

Depending on the location in the cage or the density of the hall, the actual dose received varies.

→ As a result, the dispersion of the titer (SD) increases and the CV increases.

2. Better control of contact with the target tissue

In the eye method:

The vaccine comes into direct contact with the conjunctiva of the eye and the associated lymphatic tissue (Harderian gland).

This tissue plays an important role in stimulating local and general immunity.

✅ Therefore, a stronger and more uniform immune response is induced.

But in spray:

The penetration of droplets into the respiratory tract depends on the size of the droplets, humidity and ventilation.

Large droplets remain in the nose, small droplets may not be inhaled.

→ Differences in antigen delivery to the effective site increase CV.

3. Effect of environmental conditions and operator

In spray:

Ambient temperature, wind direction, nozzle type and skill of the sprayer all affect distribution.

Birds far from the spray source usually receive less vaccine.

→ Less uniformity ⇒ High CV

In ocular:

Injection is done individually, environmental variables are almost eliminated.
→ Low CV and more reliable vaccination

🔹 4. Stress level and immune response

Ocular vaccination is usually administered with less stress and more control.

In spraying, group stress (noise, light, crowding) can reduce the immune response of some birds.

Stress causes differences in titers and increases CV.