Odour & Ammonia (1)

The odour associated with egg production comes primarily from the droppings and is a complex mixture of different gases, depending on many factors including the age of the droppings, the diet fed to the hens, the ambient temperature and humidity. COGEO like to focus on the "odour" aspect of the volatile substances associated with intensive poultry units, rather than their toxic nature (1).

Hen droppings are a mixture of solids and uric acid, which is a white solid, sparingly soluble in water and responsible for causing kidney stones and gout in humans. Microbial colonies can break down the uric acid, generating ammonia and this process continues when the droppings are collected, stored as manure and in the soil when used as a fertilizer (2). Chemical modification continues to occur in the soil with the formation of nitrates, which cause acidification of the soil and the release of nitrous oxide (N2O), a potent greenhouse gas. (7).

Ammonia is a colourless gas with a strong recognisable odour and is harmful to hens, causing respiratory problems and a reduction in egg-laying, so there is an incentive to maintain the ammonia concentration in the atmosphere of chicken sheds at a low level (less than 20 parts per million (ppm) (3). This is achieved by venting the air from the sheds into the atmosphere. Unfortunately ammonia is also toxic to humans, other animals and plants, with lichens being particularly affected. In turn, animals and insects feeding on lichens will be adversely affected. Releasing large quantities of this gas into the atmosphere is not really an environmentally desirable process.