The main ingredient in those energy drinks that makes them an 'energy drink' is an organic substance called Taurine. It is named after the Latin word Taurus which means bull. This ingredient helps energy drinks to give an energy boosted feel to whoever consumes it. In earlier times Taurine was extracted from bull semen. But it's a costly process. Energy drinks brands never go for that option as it is not feasible. So these companies will go for another sources such as meat, fish etc to make Taurine synthetically in their labs. Taurine is also present in human intestine, body tissues and even in breast milk.
So don't worry about that semen part in your favourite drinks.