Infectious bronchitis
A respiratory disease that costs you kidneys and eggshells. Vaccine protection is serotype-specific, which is why a vaccinated flock can still break.
Awaiting veterinary review. This guide is written from published industry practice and has not yet been checked by our domain advisor. Confirm anything clinical with your own veterinarian before acting on it.
Infectious bronchitis is a coronavirus, and it is one of the most contagious diseases in poultry — it moves through a shed in days. What it costs you depends entirely on what kind of bird you are running.
In broilers
Primarily respiratory: gasping, coughing, sneezing, nasal discharge, and a rattle audible at night when the fans are down.
Mortality from IB alone is usually modest. The damage is the same pattern as H9N2 — a damaged respiratory tract that bacterial infection then colonises, with E. coli the usual follower. The secondary infection does most of the killing.
Growth falls back and the flock finishes uneven.
In layers
This is where it is genuinely serious.
- Egg production drops, sometimes sharply
- Shell quality collapses — soft, thin, misshapen, rough or wrinkled shells
- Internal quality suffers — watery whites
- Some strains damage the oviduct permanently in young birds, producing hens that never lay properly. These are sometimes called false layers.
A production drop with visibly poor shells is a pattern worth investigating immediately rather than waiting to see whether it recovers.
The serotype problem
There are many IB serotypes circulating, and cross-protection between them is incomplete. A flock vaccinated against one strain may have little protection against another.
This is the central practical difficulty with IB. Vaccinating is not one decision, it is a decision about which strain — and getting that wrong looks identical to not vaccinating at all.
Which strains are circulating locally is information your vet and your hatchery have and you probably do not. Ask.
Vaccination
IB vaccine is commonly given as a combined ND+IB product rather than separately, often as the primary dose in the first week by eye drop, spray or drinking water.
Eye drop gives a more reliable take than water for the primary dose. As with every live vaccine, chlorinated water inactivates it — skim milk powder in the water neutralises the chlorine.
IB vaccine reference → · Vaccination schedule →
Telling it apart
IB, Newcastle, H9N2 and mycoplasma all present as respiratory disease and overlap heavily. You cannot reliably distinguish them by looking, and treating the wrong one costs days you do not have.
The differentiators a vet will use — lesion patterns, laboratory confirmation, which age group is affected, whether egg quality changed — are why the call is worth making early rather than after a week of guessing.
Management that helps
Ventilation, again. Ammonia and dust damage the respiratory lining that the virus and its bacterial followers then exploit. A shed with good air quality gets off lighter from every respiratory disease on this list.