WITH "hormone-free", "cage-free" and "antibiotic-free" becoming common labels on our supermarket shelves, might "pain-free" be the next sticker slapped onto a rump roast?
As unlikely as that may seem, progress in neuroscience and genetics in recent years makes it a very real possibility. In fact, according to one philosopher, we have an ethical duty to consider the option.
"If we can't do away with factory farming, we should at least take steps to minimise the amount of suffering that is caused," says Adam Shriver, a philosopher at Washington University in St Louis, Missouri. In a provocative paper published this month, Shriver contends that genetically engineered pain-free animals are the most acceptable alternative (Neuroethics, DOI: 10.1007/s12152-009-9048-6). "I'm offering a solution where you could still eat meat but avoid animal suffering."
Humans consume nearly 300 million tonnes of meat each year. Our appetite for flesh has risen by 50 per cent since the 1960s, and the trend looks set to continue. Most of this will likely come from factory farms, notorious for cramped quarters and ill treatment of animals. Battery farm chickens, for instance, routinely have part of their beaks removed without anaesthetic or pain relief to prevent them from pecking their neighbours.
Progress in understanding and manipulating the molecular and genetic bases for pain means ethics and economics, not technical feasibility, may end up determining whether Shriver's proposal becomes a reality.
For instance, mice lacking a gene called Nav1.7 are less sensitive than normal rodents to heat and pressure (Proceedings of the National Academy of Sciences, vol 101, p 12706). By similarly blocking the sensation of pain in livestock, practices like debeaking would potentially be "much more humane", says Shriver.
One objection to the idea of knocking out pain in livestock is that it could mean they put themselves in harm's way. In 2006, researchers identified six children from three Pakistani families with mutations that inactivated one particular gene. None of the children had ever felt pain, though they appeared otherwise healthy. All the kids had bruises and cuts, and one, who was known to place knives through his hand and walk on coals, died after jumping off a roof (Nature, vol 444, p 894).
There could be a way around that problem. Recent research indicates that the sensation of pain is distinct from the unpleasantness, or "affective pain", connected with it. This suggests it might be possible to eliminate the suffering caused by pain without tampering with the physical sensation.
"We know that you can dissociate the sensation from how much it bothers you," says Martha Farah, a cognitive neuroscientist at the University of Pennsylvania in Philadelphia. For instance, people on morphine feel pain, but are less troubled by it than they would be without the drug.
Studies have linked affective pain in humans to neurons in a region of the brain called the anterior cingulate cortex. Some people with lesions in this area can sense pain but don't describe it as unpleasant. Surgeons occasionally excise portions of the ACC to rid patients of debilitating chronic pain.
It's impossible to know how animals such as cows, pigs and rodents feel about pain, but "it seems plausible that the ACC is playing a similar role", Shriver says.
A recent study showed that rats with ACC damage behaved as though they were less affected by pain. They would recoil in response to an electric shock, but given the choice between staying in the dark - which rats prefer - and avoiding shocks in a lighter chamber, rats with ACC lesions opted for shocks (Experimental Neurology, vol 197, p 22).
Performing brain surgery on livestock wouldn't be feasible on an industrial scale. Livestock would have to be genetically engineered to be pain-free for it to be profitable.
Zhou-Feng Chen, a neuroscientist at Washington University in St Louis and colleagues are identifying the genes that regulate affective pain. Already, they have engineered mice that lack two enzymes which help neuron-to-neuron communication in the ACC. When the team injected a noxious, painful chemical into their paws, the mice licked them only briefly. In contrast, normal mice continued to do so for hours afterwards (Neuron, vol 36, p 713). This suggests that livestock could be spared persistent, nagging pain.
Other work in Chen's lab suggests genetic engineering may do an even better job at tempering affective pain. Last year, the team identified a gene expressed almost exclusively in the ACC called P311. Mice without P311 recoiled from heat and pressure. But when the team taught their mice to associate a region of their cage with a painful formalin injection, normal mice rapidly learned to avoid that area, while those lacking P311 kept returning.
Since P311 varies little among mammals, it's possible that knocking out the gene in cows and pigs could yield comparable results, Chen says.
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