Pizzle Rot in Sheep

To deal with the cause first. Like many conditions we see in sheep, pizzle rot is the result of an interaction between a bacteria and some other factor. The bacteria is Corynebacterium renale or one of that group. These bacteria have the ability to break urea down using an enzyme, urease. The other factor is an increase in the protein level of the diet, quite common in the month before breeding to improve the condition of the rams. Once the protein in the diet from all sources rises above 16%, urine can contain more than 4% urea. This excess urea makes the urine alkaline. The bacterial urease breaks down the urea to release excess ammonia. It is this ammonia that causes a severe irritation and ulceration of the skin around the preputial opening. Once the skin is ulcerated, C. renale or other bacteria will infect it. The debris from the ulcer form a crust which may block the opening to the prepuce. The infected ulcers can spread through the opening to the mucosa of the preputial cavity. Any scar tissue formed around an untreated ulcer can permanently constrict the preputial opening to prevent extrusion of the penis at breeding.

Once the opening is blocked, urea dribbles out to stain the surrounding wool. Fly strike often follows ulceration and urine soiling of the preputial area. Internal ulceration is painful; the prepuce becomes enlarged and swollen, containing old urine and debris. If there is severe interference with urination, the ram may become uremic and die.

Treatment consists of removing the wool around the area, then removing the dead tissue in the ulcer with a debriding agent, such as a dilute hydrogen peroxide solution. Then applying an ointment containing penicillin, bacitracin or 5% copper sulphate at weekly intervals. As an alternative to an ointment, a cetrimde solution can be used. If there is a suspicion that the ulcer has spread to the mucosal of the preputial sac, penicillin injections will help the healing.

To stop dirt contaminating the treated area, the ram should be bedded on a good layer of clean straw until the ulcer has healed. Depending on the treatment the external ulcers can take a few weeks to six months to heal. Part of the treatment is to remove the cause, that is adjusting the protein level of the diet to below the critical 16% level. Forage analysis and a ration formulation based on that analysis for each stage of production should be part of the flock management.

The healing ulcer does not prevent the passage of urine, but because of the pain of extruding the penis at breeding, the ram will be very unwilling to breed. Even if the ram can breed, it should not be used as there are reports of a venereal transmission to the ewe causing an ulcerative vulvitis. The same organism can be isolated from these lesions. A ram with pizzle rot should not restart breeding until the ulcers have completely healed.