For all the environmental angst being expressed over livestock, we rarely mention its counterpart: deadstock. Most of a slaughtered farm animal cannot be transformed into edible flesh. About 60 percent of it—offal, bones, tendons, blood, and plasma—becomes abattoir waste and, as such, has to be either recycled or disposed of. Despite our earnest efforts to better understand our increasingly complex food system, deadstock reminds us that the highest costs of food production are often hidden in places we rarely venture as we track our food's journeys from farm to fork.
The livestock industry in the United States produces 1.4 billion tons of waste every year. Ranchers, butchers, and slaughterhouses have traditionally sent carcass remains to rendering plants. Relatively cost-effective and environmentally efficient, these operations—comprising what's often called "the silent industry"—have efficiently recycled the unsavory by-products of meat production, as well as downer cows, road kill, and euthanized cats and dogs, into a variety of commercial products (such as animal feed, soap, lard, candles, and "personal care products"). All things considered, rendering plants, although by no means without problems, have kept deadstock mercifully out of sight and out of mind.
But rendering plants have fallen on hard times of late. Mad cow disease, which was first identified in the U.K. in 1986, has led to costly regulations that rendering plants have passed on to their customers. In 1997, it became illegal in the United States to feed the remains of a dead ruminant to a live ruminant, thus eliminating one of the industry's largest markets: cattle feed. In 2009, the FDA made matters worse for renderers by requiring them to remove the brain and spinal cord from cows older than 30 months (thus making it especially expensive for dairies, whose cows live longer, to render deadstock). The intention behind this provision was certainly sensible—it keeps prions, the bits of the nervous system that contain mad cow disease, out of feed destined for non-ruminant animals—but its economic impact has been considerable. Costs have gone up as much as fivefold, and the industry has consolidated into fewer operations.
How this problem will be solved remains anyone's guess. Early responses, however, haven't been encouraging. On-site burial of animals has always been popular, but it's becoming increasingly commonplace with the decline of rendering plants. This legal option is certainly an improvement upon illegal off-site dumping (which anecdotal evidence also suggests is rising), but it's still a case of sweeping waste under the rug. Feedlots and ranchers basically dig their own bins and windrows and bulldoze waste into a mass grave. Burial pits are capable of holding tens of thousands of pounds of carcasses. Some states require permits to dig them, others don't. Negative impacts on water quality have been well documented both on site and downstream from burial grounds. Groundwater contamination is routine. The leaching of chloride, ammonium, nitrate, coliforms, and E. coli intensifies with rainfall and oozes for decades after burial (it can take 25 years for carcasses to decompose).
Outdoor incineration has also become more popular with the gradual decline of rendering. But incineration comes with its own rap sheet of environmental and health-related pitfalls. It reliably releases heavy metals into the atmosphere. Pyres emit pollutants including sulfur dioxide, carbon monoxide, and nitrogen oxides. Incineration is almost always used for culled animals—beasts that have been condemned to death after a disease outbreak (burying them works poorly because they can literally explode as a result of methane build up—a conditioned known as "cattle bloat"). When infected animals are burned, a host of new poisons go airborne. Without the most rigorous monitoring, these toxins easily reach the human food and water supply. All in all, incineration is a mess.
Another alternative to rendering animal carcasses is composting. This option is relatively new, with many states making it legal to compost dead farm animals in the past ten years. On paper the procedure has its merits. Animals are aerated in a giant compost bin, where they decompose to produce humus that is rich in nitrogen, potassium, and phosphorus—all of which potentially make it an excellent fertilizer. Many agriculture experts are optimistic about animal composting [pdf].
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But (there's always a "but" when it comes to animal agriculture) there are problems—some minor, others quite serious. Minor ones include the fact that bones do not compost easily or quickly. More serious problems center on the fact that what's being composted is more than animal flesh and bones. The antibiotics, growth promoters, vaccines, and array of agricultural chemicals routinely used in animal agriculture are also composted. Composting, moreover, can also concentrate naturally occurring heavy metals. Currently, states that allow the use of composted animals limit its application to relatively innocuous tasks such as growing highway wildflowers.
A final, and by far the most hopeful, option is the anaerobic digestion of slaughterhouse waste. Anaerobic digestion generates biogas (a mixture of carbon dioxide and methane that can be converted into usable energy) and sludge (which can be used as a fertilizer). Biogas digesters have proven their effectiveness in China, where more than 20 million households receive their energy for lighting and cooking from small local digesters processing all manner of organic waste.
There are, however, numerous devils lurking in the details. Digesters do a poor job of processing long-chain fatty acids, leaving behind a thick layer of fat at the end of digestion. Experts insist that digesters work best when they are small and decentralized (to minimize threats of contamination during transport), but this requirement contradicts their other insistence that digesters be "constructed far from residential areas for reasons of biosecurity and to reduce odor problems." Digesters are water-intensive. The sludge they produce can contain prions and dangerous heat-resistant bacteria—neither of which anaerobic digestion kills (not the kind of fertilizer we want). Trumping all these concerns is something more logistical: digesters are so rare that they are, for all intents and purposes, not a viable current option.
Unfortunately, the challenges we now face with respect to slaughterhouse waste and downed animals demand urgent solutions. With rendering plants on the decline, and with current alternatives beset with problems, we have every reason to start discussing deadstock with the same intensity that we discuss livestock. Next year, slaughterhouses in the United States will kill more than 10 billion animals. What will happen to the waste? The answer might seem to be beyond our power to influence. But it does give us yet another factor to contemplate before we tuck into our next animal.