Female goats are easily excited into mating by the simple presence of a male of their species nearby. A scent given off by males causes females to produce egg cells, ready for fertilization. Although the effect has been widely known for decades, the pheromone responsible for this powerful goat smell remained a mystery, until now.
Every 27 minutes, the brain of a female goat releases a burst of hormones called GnRH, which acts to regulate the reproductive cycle. Just prior to her most fertile phase, the quantities of this hormone rise dramatically in the doe, encouraging conception.
A study into this effect was led by Yukari Takeuchi, Yuji Mori, and Ken Murata of the University of Tokyo. They believed the elusive male pheromone acts on the female's pulse generator, releasing the chemicals.
To test this theory, the researchers equipped several of the animals with a helmet designed to gather gas emanating from male goats. The team looked for chemicals present in the odor of sexually-viable individuals, and compared the results to measurements taken from castrated animals. There were a wide variety of differences, each of which had to be tested.
Each time the hormones were released, they were accompanied by a burst of electrical activity from the GnRH pulse generator. Murata and his team positioned electrodes, in order to detect this signal. As the team presented the does with different scents, the pattern of neurological activity was recorded.
When the team exposed females to a container of hair from a buck, hormones were released in large quantities by GnRH pulse generators. Murata's team was able to identify the chemical responsible for the activity as a primer pheromone called 4-ethyoctanal. Primer pheromones trigger ovulation and reproduction, while releaser forms of the chemicals trigger sexual activity. This chemical normally has a smell like orange or lemon. However, it can be turned into the musk smell of goat with a simple chemical reaction, producing 4-ethyloctanoic acid.
The team found the chemical was produced in the head of bucks, so that is the area of the animals from which researchers gathered hair samples.
"We are tempted to speculate that this is a clever reproductive strategy of the male goat to alter behavior and activity of the reproduction center in the female for mating by a single molecule," Takeuchi said.
Research into the powerful effects of the male goat pheromone 4-ethyoctanal is profiled in the 27 February issue of Current Biology.
Much of the way goats sense the world around them is through tough and smell, the way we use vision and our sense of hearing. Still, authors believe this study may lead to greater understanding of what drives mating attraction both goats and other mammals, including humans.
