Taurine, according to Wikipedia, is "widely distributed in animal tissues." But, does it get excreted through semen, and has anyone found it in bull semen?
Taurine is widely found in meats and fish. It was named from the Latin word for bull (taurus) because it was first discovered in ox bile.
In recent years, the global Taurine consumption has kept growing with an GAGR of 5.5%, more than 50 kilotons in 2014.
I have no idea how much taurine is in bull semen but even if it contains a great deal, do you really think Red Bull will be using that as a source? Can you actually imagine a way of getting bull semen to extract it? The ratio of bulls to cows or steers is very small. The only reason a farmer or breeder keeps a bull is for breeding and many cows are artificially insemination from a limited number (relatively speaking) of bulls with the desired qualities.
All this is to explain to you that your question is completely inane and pointless. I can't believe anybody would actually think it could happen.
I found a few papers about the function/concentration/localization of taurine/hypotaurine in the male reproductive system of various species:
Hypotaurine, an antioxidant, may play an important role in protecting sperm from reactive oxygen species.
These results suggest that taurine plays an osmoregulatory role in chimpanzee spermatozoa, which possibly involves stabilization of the cell membrane.
These results suggest that in addition to its importance for motility taurine might stimulate capacitation. The mechanism through which taurine supports and stimulates motility is not yet known, but its use results in the first relatively “defined” in vitro capacitation medium for hamster sperm.
Taurine and/or hypotaurine are necessary compounds for sperm capacitation, fertilization and embryo development. Hypotaurine has a protective role against peroxidative damage... Hypotaurine and taurine were quantified in spermatozoa and seminal and tubal fluid of various species, and in secretions by oviduct epithelial cell layers in vitro. Significant amounts of taurine and hypotaurine were identified.
These are but a few papers I found in a cursory search. You can also see this article for what seems to be a comprehensive overview of the "physiological actions of taurine". Even though I haven't found any direct measurements of bulls, it seems safe to say that, given its function and ubiquitous nature, bull semen contains taurine.