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SIOUX CENTER, Iowa — Other than the few small luxuries afforded them, like private access to a large patch of grass, there was nothing to mark the two hornless dairy calves born last spring at a breeding facility here as early specimens in a new era of humanity’s dominion over nature. But unlike a vast majority of their dairy brethren, these calves, both bulls, will never sprout horns. That means they will not need to undergo dehorning, routinely performed by farmers to prevent injuries and a procedure that the American Veterinary Medical Association says is “considered to be quite painful.” Instead, when the calves were both just a single cell in a petri dish, scientists at a start-up company called Recombinetics used the headline-grabbing new tools of gene editing to swap out the smidgen of genetic code that makes dairy cattle have horns for the one that makes Angus beef cattle have none. And the tweak, copied into all of their cells through the normal machinery of DNA replication, will also be passed on to subsequent generations. “It’s pretty cool,” said Micah Schouten, the calves’ caretaker, looking at his charges. The uproar over the new ease and precision with which scientists can manipulate the DNA of living things has centered largely on the complicated prospect of editing human embryos. But with the federal government’s approval last week of a fast-growing salmon as the first genetically altered animal Americans can eat, a menagerie of gene-edited animals is already being raised on farms and in laboratories around the world — some designed for food, some to fight disease, some, perhaps, as pets. Just this week, researchers reported having edited mosquitoes so that they will no longer carry the parasite that causes malaria. And the power to reshape other species, scientists and bioethicists say, raises questions that are both unique to animals and may bear on the looming prospect of fiddling with our own. “We’re going to see a stream of edited animals coming through because it’s so easy,” said Bruce Whitelaw, a professor of animal biotechnology at the Roslin Institute at the University of Edinburgh. “It’s going to change the societal question from, ‘If we could do it, would we want it?’ to, ‘Next year we will have it; will we allow it?’ ” Animal breeders have for centuries scoured species for desirable traits and combined them the old-fashioned way, by selective mating. But that process can take decades to achieve a particular goal, like cows that are both resistant to disease and produce a lot of milk. And until recently, genetic engineering techniques used to manipulate DNA had been so imprecise as to make them too expensive and difficult to perform in many animals. But the new techniques, collectively called “gene editing” to reflect the relative ease of their use, have made all manner of previously impossible or impractical goals sufficiently fast and cheap for many to find worth pursuing. Using enzymes that can be directed to cut DNA at specific locations, they allow scientists to remove and replace bits of genetic code more or less on demand. “It’s like a find-replace function in the genome of these animals,” said Scott Fahrenkrug, the chief executive of Recombinetics, based in St. Paul. “It allows us to find the natural variation that exists across a species and quickly bring it under one hood.” At Roslin, for instance, Dr. Whitelaw has changed three genes in domesticated pigs vulnerable to African swine fever, which can devastate herds, to resemble those from wild pigs that are resistant to the disease. He is now breeding them to put them to the test. With a tool called Talens, Recombinetics says it has created gene-edited pigs that can be fattened with less food and Brazilian beef cattle that grow large muscles, yielding more meat that may also be more tender. Others are working on chickens that produce only females for egg-laying and cattle that produce only males, since females are less efficient at converting feed to muscle. Chinese researchers have produced meatier cashmere goats that also conveniently grow longer hair for soft sweaters, miniature pigs lacking a growth gene to be sold as novelty pets and bulky beagles lacking a muscle-inhibiting gene, an edit that could make for faster dogs. Using the most powerful of the new tools, called Crispr-Cas9, in pursuit of treatments for human disease, researchers are also altering pigs in hopes of making them grow human organs and creating “gene drives” that would ensure that the edit to make mosquitoes malaria-proof, for instance, would spread through the whole population. But the rapid advent of gene-edited animals threatens to outstrip public discussion of their risks and benefits, some scientists and bioethicists have warned. “This essay is, in essence, a plea — let’s not ignore the nonhuman part of the biosphere,” Alta Charo of the University of Wisconsin and Henry T. Greely of Stanford University cautioned in an article titled “Crispr Critters and Crispr Cracks,” to be published in The American Journal of Bioethics next month. “Not only is it much larger than the human part, but it is much more susceptible to unobserved or unfettered — but not unimportant — changes.” The discussion of gene-edited animals in farming, in particular, will most likely be colored by the existing debate over the merits of genetically engineered food, which for decades has largely centered on corn and soybeans, altered with older technology to resist pests and tolerate herbicides. Opposition to such crops, known as genetically modified organisms, or GMOs, has prompted some retailers to decline to sell food made with them, and efforts to pass legislation to label them, even as farmers have widely embraced them and scientific organizations have said they are as safe for human health and the environment as conventional crops. Many of the new generation of edited animals do not contain DNA from another species, a frequently cited concern among opponents of genetically engineered foods, which incorporate genes from bacteria. But some consumer advocates say it may be even more difficult to reach consensus on what, if anything, should be done to the DNA of animals.
