For the past few years, genome edited livestock, including pigs, cattle, sheep, goats and chickens have been coming to today’s farms (Lillico et al., 2013, Proudfoot et al., 2015, Tan et al., 2016, Yao et al., 2016). The technology could have benefits with respect to both animal welfare and the environment. For example, Tan et al., (2013) have employed TALEN-based technologies to generate cattle that lack horns. The de-horning of cattle is of questionable ethics due to pain inflicted on the animal during the process. By changing the genome of cattle to one that is polled, the animals never develop horns and thus are spared from this procedure. Another research group was able to use TALENs to knock out the gene that encodes a growth factor that acts as a negative regulator of skeletal muscle mass. The resulting animals generated far more meat on a smaller quantity of feed (Zhao et al., 2016, Jenko et al., 2015). Other groups are planning to generate chickens that produce only egg laying hens and cattle that produce only meat delivering steers. Most recently, Chinese researchers have generated goats that produce cashmere wool more effectively, so that fewer animals can produce the same amount of wool on less land. New companies such as Recombinetics are exploring new ways to produce genome-edited animals for industrial livestock.
Genome editing can be utilized to rapidly generate animal disease model systems. For example, Tan et al., (2013), were able to generate pigs which could act as models for infertility and colon cancer, respectively. Pigs can be edited to grow human organs (Garry and Garry, 2016). Gene drives (as explained below) could be created to slow the population growth of animal pests such as rats, for example, or to create disease-resistant livestock, such as pigs which are resistant to African Swine Fever, dairy cattle which are resistant to the parasite that causes sleeping sickness, or chickens which are resistant to Avian flu virus. Using a genome editing approach, the overuse of antibiotics to maintain livestock health could be greatly reduced (Saey, 2015).