The Evolution of Farm Animal Biotechnology
The domestication of farm animals starting 12,000–15,000 years ago in the Middle East was a seminal achievement in human development that laid the foundation of agriculture as it is known today. Initially, domesticated animals were selected according to phenotype and/or specific traits adapted to a local climate and production system. The science-based breeding systems used today originated with the introduction of statistical methods in the sixteenth century that made possible a quantitative approach to selective breeding for specific targeted traits. Now, with the availability of accurate and reliable DNA analysis, this quantitative approach has been extended to DNA-based breeding concepts that allow a more cost-effective but still quantitative determination of a genomic breeding value (GBV) for individual animals. The impact of these developments was dramatically enhanced with the introduction of reproductive technologies extending the genetic influence of superior individual animals. The first of these was artificial insemination (AI) that started to be developed in the late nineteenth century. Industry uptake of AI was initially slow but increased dramatically following the development of semen extenders, the reduction of venereal disease risk by inclusion of antibiotics, and most significantly the development of effective freezing and cryostorage procedures in the mid-twentieth century. AI is now used in most livestock breeding enterprises, most notably by the dairy industry where more than 90% of dairy cattle are produced through AI in countries with modern breeding structures. Embryo transfer (ET), a technology that for the first time allowed exploitation of the female genetic pool, was made possible through the major advances in the biological sciences in the later part of the twentieth century. Advances in understanding of the reproductive cycle and its hormonal control, the availability of purified gonadotropins, and improved cell and embryo culture procedures all played significant roles. ET is now being increasingly implemented in top end breeding endeavors, particularly in the top 1–2% of a given cattle population. But its real impact is yet to come as ET is the key enabler in the introduction of the next generation of enhanced breeding technologies. ET has already played a key role in advances such as in vitro production of embryos, sexing, cloning, and transgenesis. With the birth of “Dolly,” the cloned sheep, in 1996, a century-old dogma in biology, which inferred that a differentiated cell cannot be reprogrammed into a pluripotent stage, was abolished. Today, through recent developments in molecular cell biology, available protocols are efficient enough to allow commercial application of somatic cloning in the major farm animal species. This will not only further enhance the rate of genetic gain in herds and flocks but through the recent advent of precise genome editing tools allow the production of novel germlines for agricultural and biomedical purposes through the capacity to genetically modify farm animals with targeted modifications with high efficiency. This paves the way for the introduction of the precision breeding concepts needed to respond to future challenges in animal breeding, stemming from matching the demands of ongoing hyperbolic human population growth to the limited availability of arable land and environmental constraints.