New genetic engineering techniques such as CRISPR/Cas gene scissors are being used to create, e.g. farm animals with increased muscle growth. However, the use of gene scissors is frequently problematic in cattle and pigs: individual cells are often removed from the skin, then genetically engineered with CRISPR/Cas and afterwards converted into embryonic cells using cloning processes, such as those used for Dolly the sheep. As a result, there are not only problems with the altered genes, but also with gene regulation which is particularly disturbed by the cloning process. Many animals are born sick and die shortly after birth.
One particular project being pursued by scientists is to use genetic engineering techniques to produce so-called "double muscle animals". In various experiments with pigs, cows, sheep and goats, attempts have been made to switch off the myostatin gene (MSTN) which controls muscle growth. As a result, the muscle cells should multiply at an unnatural rate. However, this can cause considerable animal health problems: experiments in China show that only eight piglets out of 900 genetically engineered embryos survived with the desired genetic engineered changes. Many also died in the first few months. The piglets suffered from health problems such as thickened tongues. After many more attempts, seemingly healthy specimens were born. However, making statements about their actual health is difficult because they were slaughtered early for further investigation.
This example shows that genome editing in farm animals is by no means free of side effects and is often associated with animal suffering. Eating food derived from these animals can also pose risks.