Interpretive Summary: Reproduction in domestic ruminants during the past 50 yr: discovery to application.
By: Jackie Walling
An article in the July 2018 Issue of the Journal of Animal Science discusses the progression of reproductive discoveries in domestic ruminants dating back to the 1600s when anatomical studies of reproductive organs began. Cattle studies addressed explain the development of Artificial Insemination (AI), the estrous cycle, and ovarian function as well as the problems associated with anestrus and embryonic/fetal mortality. This historical recount examines conceptus development and establishing pregnancy, later branching into recent reproductive techniques: embryo transfer, in vitro fertilization, cloning, transgenics, and gene editing.
AI has become the most crucial technique in breeding industries. The first methods employed rectal massage to collect semen from cattle using tubes and funnels. This was done shortly after Russian Professor Ivanov began studying semen wiped from freshly bred mares in 1899. His work contributed to developments in semen collection, evaluation, and processing. In 1914, the first artificial vagina was constructed and later modified to increase sperm yield by enacting ways to warm the AV and provide pressure.
The 1940s experimented with nutrient components of extenders (solutions to prolong sperm life) starting with a buffered egg yolk solution. Later, milk lipoproteins were added along with antibiotics. The 1960’s extenders maintained pH, reduced oxygen content, and increased fertility by use of Caprogen (contains catalase as antioxidant). Semen viability went from a 24-hour life to lasting more than a year with the gradual progression of extender development and invention of cryopreservation. Effective cooling methods favored semen survival, reduced bacterial growth, and overall increased the lifespan of sperm.
AI became significantly useful with the simultaneous developments in understanding the estrous cycle and ovarian function. In the 1920s, known as the “Heroic Age of Reproductive Endocrinology”, hormones were purified and concentrations measured using newly developed radioimmunoassays (RIAs). Researchers determined the hypothalamus controlled the pituitary gland, the use of GnRH synchronized follicular waves (inducing ovulation), and prostaglandin F2α was identified as a useful application to synch estrous cycles. Inducing ovulation became beneficial to alleviate anestrous expression (reducing reproduction efficiency) at the beginning of breeding seasons.
Preventing embryonic/fetal mortality and detecting viable pregnancies early became of upmost interest and was monitored by interactions between the uterine environment and conceptus development. RIAs isolated pregnancy-specific protein B from the placenta of cattle helping to determine the time of maternal recognition of pregnancy (MRP). The role of prostaglandins were also analyzed for their effect on MRP. To help curb mortalities, progesterone therapy was utilized and shown to improve conceptus development.
The cascade of reproductive events through the 1900s made it possible to create life by the use of embryo transfer, in vitro fertilization, cloning, transgenics, and gene editing. Embryo transfer drastically improved between 1970 and the 1990s. A successful transfer requires exceptional knowledge in the timing of the estrous cycle and information garnered from trials has paved the way for other techniques. The 1980s turned to cloning, the famed Dolly, and stem cell biology along with in vitro fertilization producing its first calf in 1981. Transgenics and gene editing found different ways to insert DNA into cells and has recently taken off with the discovery of CRISPR. As studies continue, more knowledge will breed new ideas and ways of manipulating reproductive practices for the better.
For the complete history of reproduction, visit the Journal of Animal Science.