The meat industry continues to feed medically important antibiotics to factory-farmed chickens, fish, pigs and cattle. These are given to speed up the growth of the animals and to prevent the spread of diseases in the cramped and unhygienic environment that prevail on animal factory farms.

Antibiotics are not the only chemicals administered to factory farm animals. Many animals are fed growth-promoting hormones, appetite stimulants and pesticides, fertilisers, herbicides and aflatoxins that collect in the animals' tissues and milk and which can form a toxic residue in animal tissue. This animal tissue is then sold to meat consumers.

A strong scientific consensus exists that this practice fosters antibiotic resistance in bacteria to the detriment of human health.

With the discovery of vitamins A and D, animals began to be kept in cramped and unhygienic conditions on factory farms. The addition of these vitamins in their feed are supposed to compensate for the lack of exercise and sunlight, allowing large numbers of animals to be raised indoors year-round. These animals are confined to small cages with metal bars, ammonia-filled air and artificial lighting or no lighting at all. They are subjected to beak searing, tail docking, ear cutting and castration, all so as to ensure the growth of more animals in a smaller space.

According to hsus.org, this confinement of animals causes huge strains on their immune systems so that even normal body processes like growth are impaired. This creates an ideal setting for bacteria and disease to spread rapidly. The meat industry uses antibiotics to compensate for these inhumane practises.

According to the Centre for Disease Control and Prevention (CDC), at least 17 classes of antimicrobials -- a larger category including antibacterial antibiotics, anti virals, and anti parasitic drugs -- are approved for farm animal growth promotion in the United States, including many families of antibiotics, such as penicillin, tetracycline, and erythromycin, all medicines which are critical for treating human disease.

The Union of Concerned Scientists (UCS) estimates that 70 per cent of antimicrobials used in the United States are fed to chickens, pigs, and cattle for non-therapeutic purposes.

According to Michael Greger, director, Public Health and Animal Agriculture, Humane Society of the United States (HSUS), “antibiotics and antibiotic-resistant bacteria can be found in the air, groundwater and soil around factory farms and on retail meat and people can be exposed to these pathogens through infected meat, vegetables fertilised with raw manure and water supplies contaminated by farm animal waste. Resistance genes that emerge can then be swapped between bacteria.”

A DNA fingerprinting study by Italian researchers in 2007 showed that antibiotic-resistance genes could be detected directly in chicken meat and pork.

The world’s leading medical, agricultural and veterinary authorities, all agree that antibiotic overuse in animal agriculture is contributing to human public health problems.

The writer is an environmentalist and former head, Peta, India