Reproductive disorders can have a major effect on small ruminants, often negatively impacting animal welfare and contributing to significant economic losses (Gouletsou et al. 2015). Ulcerative posthitis, or "pizzle rot", has been found to affect both wethers and rams in Australia and internationally in the UK, South Africa, New Zealand, Spain and Morocco. Studies in the late 1900s found that this ulcerative bacterial infection of the prepuce and surrounding skin is caused by multiple factors, including high protein diets, low testosterone and the presence of a urease-producing bacteria (Oslington 1997). In regions where posthitis causes significant disruption, research has been conducted to review various treatment and management methods.
Ulcerative posthitis is commonly found to affect wethers residing in areas of high rainfall with lush pastures. The highest prevalence has been reported in Australian mobs (Gouletsou et al. 2015; Loste et al. 2005), typically on the east coast, Tasmania and Victoria. Southcott (1970) had occasional reports from south-western Queensland, South Australia and Western Australia (Oslington 1997).
Although thought to be a disease of wethers, there have been reports of ulcerative posthitis in rams as well. The evaluation of breeding soundness examinations (BSE) of rams in Spain found that ulcerative posthitis is one of the most common genital alterations affecting rams, with a high proportion of aged rams in the study sustaining lesions on their prepuce. They also found that affected rams were more susceptible to blowfly myiasis (Mozo et al. 2015). Another study conducted on rams in the United States also found many rams with preputial lesions characteristic of pizzle rot (Van Metre et al. 2012).
The causative agent for the majority of cases of posthitis, including both studies that looked at prevalence in rams, was Corynebacterium renale (Mozo et al. 2015; Van Metre et al. 2012). C. renale is a gram-negative rod that is classified as a normal bacterium found in the prepuce of sheep, but proliferation of bacteria leads to disease. There are occasional reports of Streptococcus zooepidimicus, Histophilus ovis, Actinomyces pyogenes and Mycoplasma species having been isolated from lesions (Pritchard et al. 2008).
There are several factors that have been suggested to increase the risk and assist with the progression of ulcerative posthitis. High protein diets (>16%) typically lead to a higher concentration of urea excreted in urine as the amount of urea in rams’ urine is proportional to the protein level in the diet. This alkaline environment promotes the proliferation of organisms such as C. renale, which then rapidly break down the urea and produce ammonia. Accumulation of alkaline urine containing high levels of ammonia causes severe irritation and scalding to the preputial skin. Lesions are often superficial on the outer prepuce, however severe ulceration at the preputial orifice that is left untreated for long periods of time can cause stenosis or necrosis to the mucosal surface (Loste et al. 2005; Gouletsou et al. 2015; Oslington 1997).
Some studies have also found low testosterone levels in rams or wethers to promote the occurrence of ulcerative posthitis, as higher levels of testosterone increased the body’s ability to recycle nitrogen, thus resulting in less urea excreted in urine (Oslington 1997).
Previously slow-release hormonal implants containing testosterone proprionate were considered an effective method for treating outbreaks and also as prophylaxis for wether flocks.
Recently it has been suggested that ulcerative posthitis is self-limiting and should resolve with basic hygiene and cleaning of wounds. Additionally, diet modification is often recommended to one that is lower in protein to discourage proliferation of organisms, such as C. renale. Several methods of surgical correction have been mentioned in some studies, however they are not commonly performed on ruminant species.
In winter 2003, there was an outbreak of pizzle rot affecting rams in Spain that were fed a diet rich in legumes. The rams affected were up to four years of age and, other than the preputial lesions, they were clinically well and in good condition. C. renale was isolated from preputial swabs and all affected rams were treated successfully with diet modification and topical ointment containing prednisolone, bacitracin and neomycin sulphate (Loste et al. 2005).
Unfortunately, vaccination trials involving both live and killed vaccines have been unsuccessful with no significant difference between control and treatment groups (Oslington 1977). Hence, it is recommended that routine clinical examination and properly formulated rations be part of flock management. These practices will reduce the likelihood of infection and also enable timely treatment of lesions (Loste et al. 2005).
Ulcerative posthitis, although typically seen in wethers, has occasionally been reported to affect rams. Further research into the current prevalence and distribution of this disease would be beneficial for producers, especially those in Australia. This research would enable them to better manage and treat their sheep flocks and minimise annual reproductive losses.