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Even though a woman's ovulation period ends the day she begins her menstrual cycle, she can still become pregnant. Why?

An international team of scientists at the University of Saskatchewan discovered that a protein in semen acts directly on the female brain to prompt her to ovulate.

Researchers write, " the semen acts as a hormonal signal, working through the hypothalamus of the female brain and the pituitary gland. This triggers the release of other hormones that signal the ovaries to release an egg (or eggs, depending on the species)."

Scientists also suggest that the same molecule regulates the growth, maintenance and survival of nerve cells, according to US sources.

Gregg Adams, a professor of veterinary biomedical sciences at the Western College of Veterinary Medicine at  US who led the research team explains his findings.

"from the results of our research, we now know that these glands produce large amounts of a protein that has a direct effect on the female," says Adams, "As it turns out, [the protein, dubbed ovulation-inducing factor (OIF) and the nerve growth factor (NGF), are the same molecule. Even more surprising is that the effects of NGF in the female were not recognized earlier, since it's so abundant in seminal plasma."

Published in the August 20, 2012 issue of the Proceedings of the National Academy of Sciences (PNAS), the study raises intriguing questions about fertility in mammals, including humans.

Humans share many common sexual factors with other mammals, the preference for monogamy for instance. The study now shows that while OIF/NGF may function differently from animal to animal, it is present in all mammals studied thus far by researchers. This implies that the hormone is an important role in reproduction in all mammals.

Though, just how it works, its role in various species, and its clinical relevance to human infertility still remains to be answered. 

While humans are said to be 'spontaneous ovulators' in that we can ovulate with or without a man, when females are inseminated our reproductive system mimcs that of a cow, where the bovine only ovulates after being inseminated, which is called 'induced ovulation.' 

However, Adam asserts, the fact that male seminal fluid has a direct affect on the female brain is interesting and can "broaden our understanding of the mechanisms that regulate ovulation and raises some intriguing questions about fertility." Scientists also say that it may give rise to new ways of looking at fertility treatments for infertile women.