I did some research and I THINK that it might be a VERY severe case of preputial eversion, also termed preputial prolapse.
This is a picture of a partial preputial eversion. Due to injury or infection, the skin lining the preputial cavity becomes swollen and edematous and prolapses through the preputial orifice; of course this just sets it up for further injury, either the bull stepping on it, or other mechanical damage from the environment (rocks, sticks etc).
Here's another one:
This sort of injury can occur during or immediately after mating, or because of chronic prolapse issues. Bos indicus breeds such as your bull are more often affected than Bos taurus breeds because their anatomy is different - the prepuce of Bos indicus is longer (on average 5.5cm longer) than Bos taurus, the preputial orifice is larger and the sheath more pendulous. Polled breeds of Bos taurus are also susceptible; they have a rudimentary retractor muscle which results in habitual or chronic preputial prolapse.
Treatment options depend on the nature of the injury, the breed, presence of infection, ability to extend the penis and the value of the animal. The medical treatment consists of controlling infection (through antibiotics) and decreasing inflammation. It is suggested that the eversion may be put back in place, by thoroughly cleaning the prolapse with betadine (or similar), covering in Epsom salts to reduce the swelling, and then manually replacing the tissue. The sheath should then be bandaged.
Surgical intervention is required where the medical treatment fails to improve the condition, or if scar tissue prevents normal movement of the prepuce and/or penis. The two main surgical methods are posthioplasty and circumcision.
Posthioplasty or 'reefing'
Circumcision
Posthioplasty has been shown to be more effective (success rate of 90%) when compared with circumcision (success rate of 43%) in returning normal function of the penis and prepuce.
If the penis can be extended before surgery, success rates are around 88% but only 36% if this cannot be achieved.
General anaesthetic gives a better success rate (100%) over local anaesthetic (63%).
The bulls in this study were returned to semen collection after surgery and recovery.