Antibiotics often end up in pet food as a result of being added to the feed of livestock, poultry and farmed fish. Substantial quantities of these bacteria-fighting drugs, which are available to humans only through prescriptions, have long been routinely administered to livestock herds and poultry flocks. This is done to boost their growth and to prevent outbreaks of diseases that tend to occur among animals living in overcrowded, factory-farm conditions. Consuming these antibiotics regularly makes treating a pet’s illnesses much harder because the pathogens in its system become resistant to these antibiotics. Chronic, low-level exposure to these drugs can also harm beneficial bacteria, known as probiotics, which counteract harmful microorganisms and play a key role in various biological processes.

Hormones are also present in unmeasured quantities in a good deal of conventional pet food. They consist of both the synthetic variety, administered to livestock and poultry to stimulate growth, and the natural kinds that come from glandular wastes and fetal tissues of pregnant cows. There is a lot of controversy surrounding the health effects of consuming hormones.

Peanut shells are another ingredient found in some conventional pet foods. Shells are particularly susceptible to contamination from aflatoxins, which have been shown to be potent carcinogens.

Definitions for Certain Pet Food Ingredients

Meat byproducts are the non-rendered, clean parts of a slaughtered animal other than the meat. Byproducts include, but are not limited to, lungs, spleen, kidneys, brain, liver, blood, bone, and stomach and intestines emptied of their contents. They do not include hair, horn, teeth and hooves.

Poultry byproducts consist of non-rendered, clean parts of slaughtered poultry carcasses such as heads, feet, and viscera. Poultry byproducts are free of fecal content and foreign matter, except in such trace amounts as might occur unavoidably in “good factory practice.”

Meat meal is defined as “The rendered product from mammal tissues, exclusive of any added blood, hair, manure, stomach, hoof, horn and hide trimmings.” It may also come from “4-D” animals considered unfit for human consumption.

Meat and bone meal is defined as “the rendered product from mammal tissues, including bone, exclusive of any added blood, hair, hoof, horn, hide trimmings, manure, stomach and rumen contents…” It may also come from “4-D” animals considered unfit for human consumption. Bone meal, while considered a source of calcium and a means of balancing mineral levels, is also likely to contain lead and other contaminants if it comes from cattle exposed to exhaust fumes and pollution. Some experts recommend when a dog is fed bone meal, it should be given cod liver oil at the same time. Cod liver oil isn’t likely to be included in dog food containing meat and bone meal.

Animal digest is “a material which results from chemical and/or enzymatic hydrolysis of clean and un-decomposed animal tissue,” exclusive of “hair, horns, teeth, hooves and feathers, except in such trace amounts as might occur unavoidably in good factory practice and shall be suitable for animal feed.”

BHA and BHT are preservatives used to keep fats from becoming rancid. They have been a source of concern ever since studies in the early 1970s showed that, when fed to pregnant mice, their offspring were born with abnormal brain chemistry. In addition, “the affected mice weighed less, slept less and fought more than normal controls.” BHA has also been listed as a carcinogen by the state of California, and both are banned or restricted by various foreign countries.

Artificial colors may make foods (including pet foods) appear wholesome and appealing, but are often derived from substances that are anything but, such as coal-tar and petroleum extracts. They’re also apt to raise serious health concerns, since a number of such hues have been found to cause cancerous growths in test animals, and to have other adverse effects, such as triggering allergies and asthma.

Ethoxyquin is a widely used preservative found in much higher concentrations in many pet foods than in foods intended for human consumption. It is also used as a pesticide, and in industry for the preservation of rubber, and is believed by many experts to be responsible for a wide range of health problems in pets, including fatal ones such as liver cancer. Ethoxyquin is also believed to compromise immune functions. Ethoxyquin is allowed in pet food at levels of up to 150 parts per million. However, based on tests that raised concerns about its effect on lactating female dogs, and possibly puppies, the FDA’s Center for Veterinary Medicine requested in 1997 that manufacturers voluntarily lower by half the maximum level allowed in dog foods.