Chickens to be household pets. Poultry farms produce more chicken waste.
The economic externality is a microeconomic concept used to explain the impact of the economic effects of the economic activity of a given economic group (in this case chicken producers) on other groups that have no relation to that economic activity (in this case, all people who do not consume chicken).
Increased chicken production leads to increased environmental pollution (due to increased slaughter) and when such pollution reaches groups that are not interested in chicken meat (such as vegetarians), a negative externality occurs.