CRISPR in Animals: Gene Editing Livestock, Pets, and Endangered Species

Introduction: Rewriting the Animal Kingdom

When most people think of CRISPR, they picture scientists in labs editing human cells to cure diseases. But some of the most dramatic — and commercially advanced — applications of gene editing are happening in animals. Farmers are breeding heat-tolerant cattle for a warming planet. Surgeons are transplanting pig kidneys into human patients. And one ambitious company is trying to bring back the woolly mammoth.

CRISPR-Cas9 and related gene-editing tools allow scientists to make precise changes to an animal's DNA: deleting genes that cause susceptibility to disease, inserting genes that confer useful traits, or tweaking regulatory sequences that control how genes are expressed. Unlike traditional selective breeding, which takes many generations and introduces unwanted genetic baggage, CRISPR can achieve targeted results in a single generation.

This article surveys the rapidly expanding world of animal gene editing — from the barnyard to the operating room to the wild — and the scientific, regulatory, and ethical questions that come with it.

Gene-Edited Livestock: Building Better Farm Animals

Slick-Coat Heat-Tolerant Cattle

As climate change drives temperatures higher, heat stress in cattle is becoming a serious agricultural problem. Heat-stressed cows eat less, produce less milk, gain weight more slowly, and suffer higher mortality rates. The economic losses in the United States alone run into the billions of dollars annually.

Some tropical cattle breeds, like the Senepol, naturally carry a mutation in the PRLR (prolactin receptor) gene that gives them a short, sleek coat — known as the "slick" phenotype. This smooth coat helps them dissipate heat more efficiently. However, these tropical breeds are not optimized for milk or meat production the way breeds like Holstein or Angus cattle are.

In 2022, Acceligen (a subsidiary of Recombinetics) made headlines when the FDA issued an enforcement discretion decision for its PRLR-SLICK gene-edited cattle. These are conventional beef and dairy breeds that have been edited using CRISPR to carry the same slick-coat mutation found naturally in tropical cattle. The result is an animal that has the productivity of a Holstein but the heat tolerance of a Senepol.

This was a landmark moment: it marked the first time the FDA determined that an intentional genomic alteration in an animal was low-risk enough to allow the products (meat and milk) to enter the food supply. The agency noted that the edit introduced a naturally occurring variant already present in other cattle, with no novel genetic material.

PRRS-Resistant Pigs

Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most devastating diseases in the global pork industry. Caused by the PRRS virus, it leads to reproductive failure in sows and severe respiratory disease in young pigs. The disease costs the US pork industry an estimated $664 million per year, and global losses are far higher.

The PRRS virus enters pig cells by attaching to a protein on the cell surface called CD163. In 2015, researchers at the University of Missouri used CRISPR to delete a specific portion of the CD163 gene (the SRCR5 domain) in pigs. The result was dramatic: edited pigs were completely resistant to the PRRS virus, even when housed alongside infected animals.

Genus PLC, through its subsidiary PIC (Pig Improvement Company), has been developing these PRRS-resistant pigs for commercial use. In December 2023, the FDA approved Genus's application for GalSafe pigs — though the PRRS-resistant line is still working through the regulatory pipeline as of early 2026. If approved, these animals could save the pork industry billions of dollars while also reducing antibiotic use, since PRRS-infected pigs are often treated with antibiotics to prevent secondary bacterial infections.

Hornless Dairy Cattle

Dairy cattle like Holsteins are typically born with horns, which must be physically removed (a process called disbudding or dehorning) to prevent injuries to other cattle and to farmworkers. Dehorning is painful and stressful for the animals, and animal welfare advocates have long pushed for alternatives.

Some beef breeds, like Angus, are naturally "polled" (hornless) due to a specific genetic variant. In 2016, researchers at Recombinetics used gene editing to introduce the polled variant into Holstein dairy cattle. The resulting calves were born without horns while retaining the Holstein genetics that make them excellent milk producers.

However, this project hit an unexpected snag in 2019 when the FDA discovered that the edited animals also contained a small fragment of bacterial DNA (an antibiotic resistance gene from the plasmid used in the editing process) that had been inadvertently integrated. This unintended insertion, while biologically harmless, complicated the regulatory picture and highlighted the importance of thorough screening of gene-edited animals.

The technology itself remains sound, and newer editing approaches have minimized the risk of such unintended insertions. The hornless cattle project demonstrated both the promise and the pitfalls of livestock gene editing.

Xenotransplantation: Pig Organs for Human Patients

The Organ Shortage Crisis

More than 100,000 people in the United States are on the waiting list for organ transplants, and roughly 17 people die each day waiting for an organ that never comes. The gap between supply and demand has grown steadily wider for decades.

Pig organs are similar in size and physiology to human organs, making pigs a logical candidate for xenotransplantation — the transplantation of organs from one species to another. But for decades, two major obstacles stood in the way: the human immune system violently rejects pig tissue, and pig genomes harbor endogenous retroviruses (PERVs) that could potentially infect human cells.

eGenesis and the 69-Edit Pig

This is where CRISPR transformed the field. In 2023, eGenesis — a biotechnology company spun out of George Church's lab at Harvard — published data on pigs that had undergone an extraordinary 69 individual genomic edits using CRISPR. These edits fell into three categories:

Knockout of pig antigens: Three genes responsible for producing sugar molecules on the surface of pig cells that trigger immediate human immune rejection (GGTA1, CMAH, and B4GALNT2) were deleted.
Inactivation of PERVs: All 59 copies of porcine endogenous retroviruses in the pig genome were simultaneously inactivated, eliminating the risk of cross-species viral transmission.
Insertion of human transgenes: Seven human genes were inserted to help the pig organs evade the human immune system and prevent blood clotting (including human CD46, CD55, thrombomodulin, and others).

The scale of this editing — 69 simultaneous changes to a living genome — was unprecedented and demonstrated the power of CRISPR multiplexing. The resulting pigs, branded as eGenesis's "humanized" organ donors, produce organs that are far more compatible with the human immune system than unmodified pig organs.

Pig Kidney Transplants in Humans: 2024-2025

The first wave of pig-to-human organ transplants arrived faster than many expected.

In March 2024, surgeons at Massachusetts General Hospital transplanted a gene-edited pig kidney from an eGenesis pig into Rick Slayman, a 62-year-old man with end-stage kidney disease. The kidney functioned immediately, producing urine and filtering waste. Slayman was discharged from the hospital after two weeks — a milestone in medical history. Tragically, Slayman died approximately two months after the transplant, though his medical team stated that his death was not believed to be related to the transplant itself.

Later in 2024, Towana Looney became the first woman to receive a gene-edited pig kidney transplant, also performed at NYU Langone Health. Her transplant showed sustained function over several weeks. At NYU Langone, another patient, Lisa Pisano, received both a pig kidney and a mechanical heart pump in a combined procedure.

In early 2025, several more pig kidney transplants were performed at multiple medical centers, with patients surviving weeks to months with functioning pig kidneys. While long-term survival data is still limited, these cases have proven the basic concept: a gene-edited pig kidney can function inside a human body and sustain life.

The FDA has been working with companies including eGenesis and United Therapeutics (which acquired Revivicor) to develop regulatory pathways for xenotransplantation. Clinical trials with formal FDA oversight are expected to launch in 2025-2026, moving from compassionate-use cases to structured studies.

Beyond Kidneys: Hearts, Livers, and More

The University of Maryland made history in January 2022 when surgeons transplanted a gene-edited pig heart into David Bennett Sr., who survived for two months. Bennett's case, while ending in his death, demonstrated that a pig heart could support human circulation. Post-mortem analysis revealed that porcine cytomegalovirus in the donor heart may have contributed to his decline, underscoring the importance of rigorous pathogen screening.

Researchers are also exploring pig livers and lungs for human transplantation, though these organs present additional immunological and physiological challenges.

De-Extinction: Bringing Back the Woolly Mammoth

Colossal Biosciences

Perhaps no gene-editing project has captured the public imagination quite like the effort to de-extinct the woolly mammoth. Colossal Biosciences, founded in 2021 by tech entrepreneur Ben Lamm and Harvard geneticist George Church, has raised over $225 million to pursue this audacious goal.

The plan is not to clone a mammoth — there is no intact mammoth DNA available for that. Instead, Colossal aims to use CRISPR to edit the genome of the Asian elephant (the mammoth's closest living relative, sharing approximately 99.6% of its DNA) to introduce mammoth-specific traits. These include:

Dense, insulating hair for surviving Arctic temperatures
Smaller ears to reduce heat loss
Increased subcutaneous fat for cold weather survival
Modified hemoglobin that functions better in cold environments

By 2024, Colossal had identified and begun editing dozens of genes associated with these cold-adapted traits. The company announced the creation of elephant induced pluripotent stem cells (iPSCs) — a critical step, since iPSCs can theoretically be differentiated into any cell type and could eventually be used to create an embryo.

The technical challenges remain enormous. Elephants have a 22-month gestation period, and no one has ever successfully performed in vitro fertilization or embryo transfer in elephants. Colossal is exploring the possibility of using artificial wombs for gestation.

Beyond the Mammoth

Colossal is also working on de-extinction projects for the thylacine (Tasmanian tiger), which went extinct in 1936, and the dodo, which disappeared in the 17th century. Each species presents unique genetic and reproductive challenges, but the underlying approach is the same: use CRISPR to edit a closely related living species to express the traits of the extinct one.

Critics argue that de-extinction is a distraction from protecting species that are alive today. Supporters counter that the technologies developed for de-extinction — including advanced reproductive techniques and genetic engineering — have direct applications in conservation.

Conservation: Saving Endangered Species

Genetic Rescue for Small Populations

Many endangered species face a genetic crisis: their populations are so small that inbreeding has reduced genetic diversity to dangerously low levels. This makes them vulnerable to disease, reduces reproductive success, and limits their ability to adapt to changing environments.

CRISPR offers the possibility of "genetic rescue" — introducing beneficial genetic variation into small populations without the need for physical translocation of animals. For example, the black-footed ferret, one of North America's most endangered mammals, was nearly extinct by the 1980s. All living black-footed ferrets descend from just seven individuals, resulting in extremely low genetic diversity.

In 2020, scientists at Revive & Restore and the US Fish and Wildlife Service cloned a black-footed ferret named Elizabeth Ann from the preserved cells of a ferret that died in the 1980s. While this used cloning rather than CRISPR, the next step in the program involves using gene editing to introduce genetic variants from the historical population into living animals, boosting the species' resilience.

Similar approaches are being explored for species like the northern white rhinoceros, of which only two females survive. Researchers at the BioRescue project have created rhinoceros embryos using stem cell technology and are investigating how gene editing could contribute to restoring genetic diversity.

Disease-Resistant Corals

Coral reefs are among the most biodiverse ecosystems on Earth, but they are dying at an alarming rate due to ocean warming, acidification, and disease. Scientists at institutions including Stanford University, the Australian Institute of Marine Science, and the Hawaii Institute of Marine Biology are exploring whether CRISPR can help.

Research teams have used CRISPR to edit genes in coral that are involved in heat stress response, with the goal of creating corals that can withstand higher water temperatures. While this work is still in early stages, preliminary results have shown that edited coral larvae can survive temperatures that would bleach or kill unedited corals.

The challenge with coral conservation is scale — there are billions of individual coral colonies across the world's reefs. Gene editing a few corals in a lab will not save reefs on its own. Instead, the hope is that edited corals with enhanced heat tolerance could be used as "seed stock" for reef restoration projects, gradually introducing heat-resistant genes into wild populations.

Gene Drives: Rewriting Wild Populations

Eliminating Malaria-Carrying Mosquitoes

Gene drives are perhaps the most powerful — and controversial — application of CRISPR in animals. A gene drive is a genetic system that ensures a particular gene is inherited by nearly 100% of offspring, rather than the usual 50%. Over multiple generations, a gene drive can spread a trait through an entire wild population.

The primary target is the Anopheles mosquito, which transmits malaria. Malaria kills over 600,000 people per year, the vast majority of them children in sub-Saharan Africa. Traditional control methods — bed nets, insecticides, antimalarial drugs — have saved millions of lives but have not been sufficient to eliminate the disease.

Target Malaria, a research consortium funded partly by the Bill and Melinda Gates Foundation, is developing CRISPR-based gene drives that could either suppress mosquito populations (by spreading genes that cause female infertility) or modify them (by spreading genes that prevent the mosquitoes from carrying the malaria parasite).

In laboratory trials, gene drives have successfully crashed Anopheles mosquito populations within a few generations. The technology has been tested in contained settings in Burkina Faso, where non-gene-drive sterile male mosquitoes were released as part of a phased research program. A release of gene-drive mosquitoes into the wild has not yet occurred, pending further safety testing, regulatory approvals, and community engagement.

The Ecological Risks

Gene drives are unlike any other gene-editing application because they are designed to spread through wild populations. Once released, a gene drive cannot easily be recalled. This raises serious ecological questions:

What happens to the food web if Anopheles mosquitoes are eliminated? (Many species eat mosquitoes or their larvae.)
Could the gene drive jump to non-target mosquito species?
Who has the authority to release a gene drive that could cross national borders?

Researchers have proposed "daisy chain" gene drives and other self-limiting designs that would spread through a population for a limited number of generations before fading out. These could provide the benefits of a gene drive while reducing the risk of irreversible ecological changes.

FDA Regulation of Gene-Edited Animals

The regulatory landscape for gene-edited animals is complex and evolving. In the United States, the FDA regulates intentional genomic alterations (IGAs) in animals under the same framework used for new animal drugs. This means that a gene-edited cow must go through a regulatory review similar to that of a new veterinary pharmaceutical — a process that critics argue is disproportionately burdensome for edits that introduce naturally occurring genetic variants.

Key Regulatory Milestones

2020: The FDA approved AquAdvantage salmon, a genetically engineered (not CRISPR-edited) Atlantic salmon that grows faster, making it the first genetically engineered animal approved for food use in the US.
2020: The FDA approved GalSafe pigs (developed by Revivicor), which lack a sugar molecule (alpha-gal) that can cause allergic reactions in some people. These pigs were approved for both food and potential medical use.
2022: The FDA issued an enforcement discretion for PRLR-SLICK cattle, signaling a more flexible approach for low-risk edits that replicate naturally occurring variants.
2024: The USDA proposed taking a larger role in regulating gene-edited animals intended for food, which could streamline the process for agricultural applications.

International Approaches

Different countries have taken very different regulatory approaches:

Japan approved the sale of gene-edited foods beginning in 2021, including a GABA-enriched tomato and gene-edited red sea bream (a fish edited to have more edible flesh). Japan treats gene-edited organisms that do not contain foreign DNA differently from traditional GMOs.
The European Union has historically regulated gene-edited organisms the same as GMOs, but in 2024 moved toward new legislation that would create a more permissive pathway for gene-edited plants (the status of animals under the new framework remains under discussion).
Brazil and Argentina have regulatory frameworks that distinguish between gene-edited organisms and traditional GMOs, creating more streamlined pathways for approval.
China has invested heavily in gene-editing research for livestock, including disease-resistant pigs and high-muscle sheep, though its regulatory framework is still developing.

Ethical Debates

Animal Welfare

Gene editing raises complex animal welfare questions. On one hand, creating disease-resistant animals could dramatically reduce suffering — no more PRRS outbreaks in pig barns, no more painful dehorning of cattle. On the other hand, critics worry that gene editing could be used to push animals further toward extreme productivity (even faster growth, even higher milk yields) in ways that compromise their wellbeing.

There is also the question of off-target edits. While CRISPR is remarkably precise, it can sometimes make unintended changes elsewhere in the genome. In livestock bred for food, these off-target effects could have health consequences for the animal or, theoretically, for consumers — though no evidence of harm has been found to date.

Environmental Concerns

Gene-edited animals that escape into the wild could potentially interbreed with wild populations, introducing edited genes in unpredictable ways. This concern is especially acute for gene-edited fish. The AquAdvantage salmon, for instance, is required to be raised only in contained, land-based facilities to prevent escape into the ocean.

Gene drives represent the extreme case: they are explicitly designed to alter wild populations. The question of whether humans should intentionally modify entire ecosystems — even to save hundreds of thousands of lives from malaria — is one of the most profound ethical questions in modern biology.

De-Extinction Ethics

The woolly mammoth project raises its own set of questions. Even if Colossal succeeds in creating a mammoth-like animal, it would be born without a herd, without a culture, and without the learned behaviors that mammoth calves would have acquired from their mothers. Is it ethical to create an animal for which no natural social environment exists?

There is also the opportunity cost argument: the hundreds of millions of dollars spent on de-extinction could fund enormous conservation efforts for species that are alive today and still saveable.

Commercial Products and the Road Ahead

Several gene-edited animal products are already available or nearing market:

AquAdvantage salmon: Available for sale in the US and Canada, the first genetically engineered animal approved for human consumption.
Gene-edited red sea bream and tiger puffer fish: Available in Japan since 2021, these fish have been edited to grow faster and larger.
PRLR-SLICK cattle: Meat from these heat-tolerant cattle can enter the US food supply following the FDA's enforcement discretion decision.
GalSafe pigs: Approved for food and medical use in the US.

Looking ahead, the pipeline includes PRRS-resistant pigs, gene-edited chickens resistant to avian influenza (being developed by researchers at the Roslin Institute in Edinburgh), and cattle edited for improved feed efficiency or reduced methane emissions.

The pet industry has also begun exploring gene editing, though primarily in research contexts. Hypoallergenic cats, created by editing the Fel d 1 gene responsible for cat allergies, have been proposed by multiple companies, though none have reached market as of early 2026.

Conclusion

CRISPR gene editing in animals is no longer a futuristic concept — it is happening now, in commercial livestock operations, hospital operating rooms, and conservation labs. The technology offers genuine solutions to pressing problems: feeding a growing population in a warming climate, saving lives lost to the organ shortage, protecting endangered species, and fighting deadly diseases like malaria.

But each application carries its own risks and ethical complexities. The heat-tolerant cow is a straightforward quality-of-life improvement for animals and farmers alike. The gene-edited pig kidney transplant is a lifesaving intervention for patients who would otherwise die. The gene drive to eliminate malaria mosquitoes could save hundreds of thousands of children per year — but carries ecological risks that are impossible to fully predict.

What is clear is that society cannot afford to ignore these technologies. The questions they raise — about animal welfare, ecological risk, regulatory oversight, and the limits of human intervention in nature — will only become more urgent as the tools become more powerful and the applications more widespread.

Sources and Further Reading

Acceligen / Recombinetics. "PRLR-SLICK Gene-Edited Cattle." FDA Enforcement Discretion Decision (2022). FDA.gov
Burkard, C. et al. "Precision engineering for PRRS-resistant pigs." PLOS Pathogens (2018). doi:10.1371/journal.ppat.1006831
Whitworth, K.M. et al. "Gene-edited pigs are protected from porcine reproductive and respiratory syndrome virus." Nature Biotechnology 34, 20-22 (2016).
Niu, D. et al. "Inactivation of porcine endogenous retrovirus in pigs using CRISPR-Cas9." Science 357, 1303-1307 (2017).
eGenesis. "69-Gene Edited Pig for Xenotransplantation." Company publications (2023). egenesisbio.com
Massachusetts General Hospital. "First Gene-Edited Pig Kidney Transplant in a Living Patient." Press release (March 2024).
Griffith, B.P. et al. "Genetically Modified Porcine-to-Human Cardiac Xenotransplantation." New England Journal of Medicine 387, 35-44 (2022).
Colossal Biosciences. "De-Extinction and Species Restoration." Company publications. colossal.com
Revive & Restore. "Black-Footed Ferret Genetic Rescue." Project summary. reviverestore.org
Target Malaria. "Gene Drive Research for Malaria Control." targetmalaria.org
Hammond, A. et al. "A CRISPR-Cas9 gene drive system targeting female reproduction in the malaria mosquito vector Anopheles gambiae." Nature Biotechnology 34, 78-83 (2016).
FDA. "Intentional Genomic Alterations in Animals: Guidance for Industry." US Food and Drug Administration (2022). fda.gov
Kyrou, K. et al. "A CRISPR-Cas9 gene drive targeting doublesex causes complete population suppression in caged Anopheles gambiae mosquitoes." Nature Biotechnology 36, 1062-1066 (2018).
Clements, T. et al. "Gene editing of coral for climate resilience." Research summaries, Stanford University and Australian Institute of Marine Science (2023-2025).
Van Eenennaam, A.L. "Application of genome editing in farm animals: Cattle." Transgenic Research 28, 93-100 (2019).