Animals may be given insufficient space, light, ventilation and comfort, causing stress, malformation, loss of productivity and infertility. Under such conditions stress and malformation occur, as well as loss of productivity. Inadequate housing may also occur through negligence or through ignorance of the optimum conditions required and of animal psychology and behaviour. With breeding animals it may lead to infertility, rather than the desirable peak condition.
Factory farming is a very attractive commercial proposition for industrial investors and with a greater demand for meat and egg products and a comparatively higher standards of living in these countries, the trend towards intensive farming methods is likely to increase. The competition for land space also contributes to the trend. Factory farming is characterized by the widespread use of antibiotics in animal feeds, which could lead to drug resistance in bacteria pathogenic to both humans and animals. Hormones, which may cause cancer in humans, are used as implants to stimulate growth in beef cattle. Pesticides, nitrate fertilizers, herbicides and moulds (aflatoxins), contaminate grains and other crops used in the animals' feed. Some of these substances, which are hazardous to humans if ingested in sufficient amounts, may be stored in the animal's fat, muscles and internal organs, or be concentrated and excreted in milk, which is ingested by humans. Although some of these substances are identified animal carcinogens, their use is often justified on the grounds that they help reduce production costs.