What's in animal feed?

Ingredients are often added to the food of animals in factories to make them grow faster and larger, or for other reasons. Many of these additives are substances that could have damaging effects on people if they are consumed. Most governments regulate the maximum level of ‘residues’ of additives that are allowed in food for human consumption.

Antibiotics

For the last few decades, many farmers have been feeding animals (particularly chickens and pigs) low doses of antibiotics routinely in their feed or water, because it was found that this increased the animals’ growth rate. It also protects them against diseases which can be passed between animals kept in overcrowded conditions.

Parasite control

Poultry kept together in large numbers are a breeding ground for internal parasites called coccidia, which cause diarrhoea. To prevent this, medicines (known as coccidiostats) are often put in the animals’ feed in factory farms to control the parasites. Residues of coccidiostats can contaminate the animals’ meat. Some of these substances are toxic to humans and are only allowed to be present in the meat in very low quantities. However, in the UK in 1999 it was found that 17.8 per cent of chicken livers tested had residues of coccidiostats in excess of the maximum residue limit of 200 micrograms per kg, the highest residue found being 50 times the permitted level.

Sometimes feed can become contaminated with illegal additives accidentally, for example at feed mills or in farmers’ stores. In the UK, the potentially toxic coccidiostat lasalocid is banned for feeding to laying hens, because of the possibility that it can contaminate eggs. In spite of the ban, in 2003 the UK’s regulators found that residues of lasalocid in eggs were five and a half times higher than in the previous year, presumably due to accidental or careless contamination of the hens’ feed.

Chemical additives

Many intensive farms use animal fat to supplement the feed given to animals such as chickens and farmed fish. Because some toxic chemicals, such as polychlorinated biphenyls (PCBs), dioxins and organochlorines, accumulate in the fatty tissue of animals they can be passed to humans who eat animals that have eaten the fat-supplemented feed. These chemicals are known as Persistent Organic Pollutants (POPs) and they have been associated with health problems in humans such as damage to the nervous or immune system and reproductive problems. In Belgium in 1999, animal fat intended for animal feed contaminated over 15,000 tonnes of animal feed with toxic levels of PCBs and dioxins, resulting in the withdrawal of chicken meat and eggs from the market. Intensively farmed salmon contains 11 times more dioxin than wild salmon, leading some experts to recommend that people should limit how much salmon they consume.

Arsenic

Arsenic-based feed additives are given to pigs and poultry in some countries in order to increase their weight. Some of the arsenic compound is excreted in the chickens’ faeces, but some is retained in the chickens' liver. Chicken meat in the US contains three to four times as much arsenic as other types of meat.

Hormones

Growth hormones are given to cattle as implants or as injections to increase their growth rate or their milk production. In the US, 90 per cent of beef cattle and one third of dairy cows are treated with growth hormones. The possibility of the hormones affecting consumers has caused great concern, because these hormones have been linked to cancer and other health problems. Because of medical and public concern, the EU has banned the sale of hormone-treated beef, but it is known that such meat is still sold illegally and residues of at least 35 drugs have been found in meat samples in the EU.

Colourants

Canthaxanthin is a yellow/orange colourant which can be put into the feed of chickens and factory farmed salmon in order to brighten the colour of egg yolks and chicken or salmon flesh. It is originally found in plants, but the substance used for animal feed is usually synthetically made. Because it can have damaging effects on humans at high doses, governments usually set legal limits to the amount of canthaxanthin that is allowed to be used in animal feed, based on a maximum safe dose for humans. In 2002, the EU’s Scientific Committee on Animal Nutrition expressed the view that some consumers of poultry or salmon might be unknowingly eating more than the acceptable daily dose of canthaxanthin.