An undercover investigation by Animal Liberation NSW

Causes of Rapid Growth

  • Selective breeding to create larger birds has contributed to the rapid growth of chickens. Despite the health and welfare issues associated with accelerated growth, the industry considers each animal in terms of 'feed conversion efficiency'. Growing chickens faster means more profit despite the higher death rates. Selective breeding is not the only cause of accelerated growth. Inhumane on-farm practices are also used to increase the size of the chickens as detailed below.
  • Artificial lighting - chickens are often kept in near continuous lighting, with only 1-4 hours of darkness provided each night. The extra light confuses the chickens into thinking it is morning so they eat more food. The lack of darkness also keeps the birds tired as they are lacking in sleep. They are therefore less likely to walk around or move (as exercise of any kind could cause weight reduction). The lighting that is provided is a low lux lighting which isn't a fully bright light. This also ensures low exercise and high feed intake as it is bright enough to keep them awake but not so bright that it encourages them to walk around (5).
  • Overcrowding also ensures the birds can't exercise as there is so little room the birds aren't able to move around easily. Overcrowding also causes greater build-up of dust and ammonia reducing air quality which can cause respiratory disorders. Birds are often walking over the top of each other causing difficulty for chickens attempting to sleep (5).
  • Drug use - chickens have coccidiostats put into their feed. Coccidiostats are a nicarbazin which is an antibiotic type drug. They are regularly used in the broiler industry. Traditionally they are used to treat coccidiosis (a parasitic disease resulting from infestation of the alimentary canal). Often birds pass small numbers of oocysts in their faeces without negative effects. Coccidiosis becomes important when animals live in conditions that permit the build-up of oocysts (in the faeces) in the environment (6), for example, the intensive farming of chickens.
  • Coccidiostats are routinely used in the broiler industry to avoid the common disease coccidiosis. In other words, they assume it is so likely to occur that they treat them for the illness as a preventative measure by adding it continually to feed. The build-up of infected faeces is a welfare and mortality concern. The disease can be avoided by eliminating overcrowding and providing clean and dry litter, free from manure.
  • However! There is a second, far less discussed reason for putting coccidiostats into the feed - some coccidiostats (lasalocid and monensin) also act as ionophores - increasing feed efficiency and weight gain. The drug disrupts the natural flora of the gut enhancing feed absorption and allowing faster weight gain. In other words, it promotes rapid growth. Routine use of cocciostats were banned in Europe in 2006 (7).
  • Salinomycin is also regularly found in chicken feed at broiler farms. Salinomycin is a polyether, an antibiotic type drug, and is also used for the prevention of coccidiosis. Salinomycin increases nutrient absorption across cell membranes in the gut and can lead to an increase of 62% mean body weight compared to chickens who are not fed salinomycin (8).