Each year, 60 billion chickens are raised for their meat and eggs globally. They represent 70% of the biomass of all bird life on Earth.
Around 75% of chickens for meat, and around 70% of laying hens are reared in intensive farming systems which pose a wide range of animal welfare and human health concerns.
The single country which produces the most poultry is USA, with China a close second. But the whole region of Asia is home to most of the world's farmed poultry.
Encompassing both meat ("broiler") chickens and layer hens, the main issue is that human demand is so high that the numbers of birds are so vast, this does not allow producers any means by which to care for each individual animal. The conditions of these systems are therefore typically cramped and unhygienic. There are high mortality rates and often the gigantic dark sheds in which chickens spend their whole short lives are so big that carcasses go unnoticed by farm workers. Chickens are forced to live on top of each-other's faces, urine and corpses. This invites pests and disease.
In such crowded conditions, diseases such as salmonella and avian flu can easily spread through the population, causing a risk that these diseases will enter the human food chain. To counter this, birds are typically fed preventative anti-biotics. Because humans consume the meat and eggs, in turn this causes a downturn in human anti-microbial resistance. Around 75% of all anti-biotics produced today are given to intensively farmed animals.
Modern farmed chickens also bear an enormous burden on their bodies, being given growth hormones so they reach a mature size for slaughter as quickly as possible. This puts pressure on their organs and many live with agonising brittle bones. The ancestor of the modern layer hen would have naturally produced 12 eggs per year, now some modern breeds can produce around 300 eggs per year. This puts their bodies under constant stress for their whole life.
Many broiler chickens only live around 3 or 4 months, whilst layer hens live up to one year. Naturally, chickens can live up to six years. If eggs in the layer hen industry are hatched as male, they are typically put on a conveyor belt and thrown in to a macerator machine to be ground up at one day old, deemed unworthy of life.
1.4 billion pigs are slaughtered for food annually, with China being the biggest producer.
Even though the intelligence of pigs has been studied and likened to dogs, dolphins and chimpanzees, they are exploited in intensive farming systems which do not allow them to express their natural behaviours.
Studies have shown pigs to be smarter than dogs, capable of mourning, problem solving and empathy. But in spite of their high cognitive capacity, the pig meat industry subjects them to cramped, dark, conditions devoid of the enrichment they need.
Nursing sows are typically kept in gestation crates, which allow them no room at all to move whilst they suckle their young.
The cramped and unygenic conditions found in many pig farms throughout Asia mean that they are susceptible to disease such as African Swine Fever. Because ASF spreads so quickly through a population and cannot be allowed to enter the human food chain, outbreaks in recent years have lead to highly distressing mass culls, which have seen thousands of pigs being thrown in deep pits with tractors and either buried or burned alive. Totals have numbered in to the millions in national culls. There are currently neither vaccines nor cures for ASF.
For populations who do not contract ASF, they may either live in large, multi-storey "pig hotels", never feeling natural ground beneath them or seeing daylight for their entire lives. Although pigs are naturally lean, they are grossly overfed by humans to make them fat in readiness for slaughter. Pigs are stunned on their way to be slaughtered by having their throats slit, but it has been shown that stunning is not 100% effective, meaning that many pigs will be fully conscious when their throat is slit.
Investigations have shown the presence of other severely inhumane slaughter methods in Asia such as live blugeoning with a club. Without first being stunned, this is extremely stressful and painful and is typically done in the presence of many other pigs.
Around 1.5 billion cows are exploited annually around the world for their milk and meat.
Many male calves from the dairy industry are kept in tiny crates which inhibit their growth in order to producer a more desirable lean veal meat.
Milk production of modern dairy breeds is unnaturally high, putting stress on their bodies.
Cattle are a leading producer of methane, a greenhouse gas.
Although modern cattle breeds can live naturally up to 20 years, they are typically slaughtered between 2 and 5 years old for beef.
Some modern cows have been selectively bred to be more muscular to account for high meat demand and this puts more pressure on their bodies, particularly for birthing mothers who still retain narrow hips making childbirth painful and dangerous.
Likewise many dairy breeds have been bred to have unnaturally large udders and high milk production. Dairy cows must be impregnated so that they bear offspring which makes them produce milk. This insemination is often artificial using an apparatus which is known in the industry as the "rape rack". Newborn calves are separated from their mothers when only a few days old, causing both severe distress. Male calves are either shot or given to the veal industry where they are raised lean in barren crates and killed young.
In intensive farming systems, cows milk has been found to contain contaminants such as blood or puss.
Cows are large animals who must be fed for a minimum of two years before slaughter. This feeding either requires grazing land or the dedication of large volumes of crops which could otherwise feed humans. A typical feed ratio means a cow would eat 10kg in its lifetime for every 1kg of beef produced.
Much land is cleared either to provide grazing land for cattle or arable land to grow feed crops such as soy. For example this is decimating the amazon rainforest at an alarming rate. Rainforests are vital for the survival of all life on Earth.