Boldenone was reportedly patented by Ciba in 1949, and esters of the compound were developed by the company in the 1950s and 1960s.  One such ester, boldenone undecylenate, was introduced for clinical use as an injectable AAS under the brand name Parenabol in the 1960s.  However, it was discontinued for use in humans in the late 1970s.  Squibb introduced boldenone undecylenate for veterinary use under the brand name Equipoise.  The medication has been used much more widely in veterinary medicine, in which it has been used mainly in horses, and remains in use today.  
It is very common for bodybuilders to use veterinary steroids for a precontest cycle. Since they are typically assimilated quickly, they do the best work in the shortest amount of time, and are generally out of the system relatively fast in comparison to other ‘roids. And, believe it or not, usually people see fewer side effects when using vet products than when using human ones. Why take anything else? Maybe not ‘why take anything else’, but why not include veterinary steroids, in one form or another, in every cycle? In my mind, veterinary drugs should really be everyone’s choice for extreme condition and definition. They combine well with androgens and other anabolics as well as any drug in the human realm of anabolic steroids. The only problem, these days anyway, is availability. You can find them in Mexico, but you risk fakes, counterfeits, lower quality, or lower dose per ml. You also, of course, face the possibility that you’ll be stopped.