Animal Welfare and the Risks

Egg Donors and Surrogates

In the dog cloning program described in Insights from one thousand cloned dogs, researchers used abdominal surgery under anesthesia to collect eggs from donor dogs and to transfer embryos into surrogates. They also used C-sections in an effort to save puppies showing signs of fetal distress. A surrogate that never becomes pregnant can still undergo surgery to receive the embryos.

Some protocols also involve treating animals before the transfer. In a 2008 cat cloning study, researchers gave hormones to 28 cats to synchronize their reproductive cycles. Twenty of those cats then underwent surgery to receive embryos.

Furthermore, there is no explicit number of times that an animal can be used as an egg donor or surrogate, nor are pet cloning companies required to report these numbers to the public.

Failed Transfers, Stillbirths, and Early Deaths

A live birth can be the result of many embryo transfers. In the standard cloning group of a 2019 domestic-cat study, researchers transferred 151 embryos into 13 surrogate cats. One kitten was born alive.

A 2024 dog cloning study recorded outcomes at several stages. Researchers transferred 99 embryos into 10 surrogates. Four became pregnant and delivered 11 puppies. Nine were born alive and two were delivered dead. The researchers reported that the surviving puppies grew up healthy.

Developmental Abnormalities

According to researchers in the 2022 dog study, some cloned puppies had serious developmental abnormalities. Researchers observed cleft palates, underdeveloped eyes, enlarged tongues, and abnormal muscle growth. Of the 1000 pups, there were 98 cases of enlarged tongues and muscle overgrowth occurring together. This muscle condition was nearly always fatal, typically due to resulting difficulties with breathing.

A separate 2011 study examined 12 cloned puppies that were stillborn or died shortly after birth. Researchers found defects in the abdominal wall and enlarged hearts and livers, as well as enlarged tongues and excess muscle growth. They found reduced activity of a gene that normally limits muscle growth and suggested this might contribute to the abnormalities.

Long-Term Health

It is important to note that animals assessed as healthy at birth typically fared well. This can be seen across several species: when the animal is healthy at birth, it usually lives out its life like any other member of its species.