Animal Frontiers fertility issue: Sex education that everyone needs to understand

Since the beginning of recorded history, a high priority has been placed on fertility. During every civilization to date, there have been festivals, rituals, and numerous other practices promoting and celebrating the ability to reproduce. This remains very true today as well. Case in point, if one were to search the internet using only the word “fertility”, then about 48.7 million results would appear in only 0.31 seconds. This fascination with fertility is not surprising because the ability to reproduce represents the future. There is always the underlying hope that the next generation will perform better than the present and help address the challenges facing our society. Today, one of the most important of these for animal scientists is feeding a world population that is growing at a faster rate than our current ability to provide it with quality food, a situation that has been well-documented recently in numerous publications (FAO, 2010; FAO, 2012; Cao and Li, 2103; Krehbiel, 2013; Smith et al., 2013). Without fertile livestock, there is no meat, no milk, no eggs, or any other source of high quality protein from animals. Hence, continued development and refinement of management strategies that enhance reproductive events is an absolute requirement if we are to meet this daunting task. Understanding fertility in livestock has additional benefits for humans as well in that we learn something about ourselves. There are remarkable similarities between humans and domesticated animals in many reproductive processes. Production of sperm, fertilization, and embryonic development are just a few. As a result, techniques developed in livestock often are modified for humans or used to study situations that arise in humans. An excellent example of this is the discovery made by the late Sir Christopher Polge and his colleagues in the 1940s (Polge et al., 1949). They demonstrated that glycerol allowed bovine sperm cells to withstand freezing and subsequent thawing and, hence, spawned the science of cryobiology which has had unprecedented effects on our current way of life. As animal scientists continue their quest to further elucidate reproductive events, it is reasonable to assume that their future discoveries will continue to have significant impacts on human well-being as they have done so in the past. I was surprised, pleased, humbled, and a little reluctant when asked to serve as the guest editor for this issue. The challenges facing those of us that study reproductive physiology in domestic animals are complex and diverse. It often feels that we “discover” more questions than answers, but this is what keeps things interesting and exciting. Therefore, I thought it would be fitting to organize this issue of Animal Frontiers on animal fertility in a similar fashion: around questions and answers. There are six pairs of articles that follow the chronological sequence of events that must occur in animals for them to successfully produce live offspring: pubertal development, sperm production, fertilization, early pregnancy (embryonic development), late pregnancy (fetal development), and lactation. The first article in each pairing addresses important challenges or “questions” within its particular area, while its companion paper focuses mainly on a success story in which animal scientists have been able to provide some “answers” or solutions for specific fertility-related problems. While I have deliberately chosen to partition the reproductive cycle into its individual phases in this issue, it is important to recognize that successful fertility is a continuum. It is clear that the environment to which pregnant mothers are exposed can program how their offspring will perform reproductively as adults and manipulations during each subsequent phase