Definition

A plug composed of proteinaceous material and cellular debris blocking the urethra.

Clinical Signs

May observe the following:

• A firm, cream colored, material at tip of penis.
• A perceptible odor may or may not be present.

Etiology

The spontaneous formation of vesical proteinaceous plugs, otherwise commonly referred to as penile or penis plug, is frequently seen in the aging male rat. The plugs have been known to attain a large enough size to occlude the lumen of the bladder. They can be seen as firm white creamy colored material often protruding at the tip of the penis.

These plugs are formed of eosinophilic proteinaceous material mixed with exfoliated urothelial cells, cellular debris, and spermatozoa. It is believed that these plugs result from abnormal ejaculation, and the secretions from the male accessory sex glands ( refer to: Male Reproductive System of the Rat Guide)
( Lee, 1986; Mohr, Dungworth & Capen, 1992, p. 262).

In the adult male rat secretions from the accessory sex glands: secrete fluids that act as an energy source for sperm, contribute to the mobility and viability of sperm, help to lubricate the urethra and clear it of urine prior to ejaculation, and serves as a means of transporting the sperm in the female tract and creating a copulatory plug to help ensure fertilization. In addition secretions called smegma, composed of oils, moisture, and shed epithelial cells help to keep the glans moisturized. Under normal circumstances the healthy male rat is able to adequately clean the penis and sheath, and prevent the buildup of secretions. However in the aging or ill male rat, or those males with paresis, the ability or flexibility to groom may decline; hence secretions can become firm, blocking or plugging the urethra, and interfere with urination and/or lead to infection if not removed. In male rats where an orchiectomy (neuter) has been performed the development of urethral plugs is significantly decreased (Bennett, Soft Tissue Surgery, 2012, p.378).

It is important to note that in the majority of cases where urethral plugs are present there is no evidence of stone nidus formation within the plugs, and is therefore not considered a precursor to the development of bladder calculi (Mohr, Dungworth & Capen, 1992, p. 262).

Figure

• Fig. 1: Example of examination and photos of proteinaceous plug

Diagnostics

Physical observation

Bladder distention

Perceptible odor which may or may not be present

Treatment

Gently apply pressure with thumb and index finger approximately ½ cm distances on each side of the penis. Carefully massage to project penis outward from the sheath to remove the plug.

Care should be taken when removing plugs so as not to cause irritation to the tissues.

In the event the plug is very firm, applying a small amount of olive oil to the penis may ease removal and prevent irritation to tender tissue.

If infection is present an antibiotic such as enrofloxacin (Baytril) or trimethoprim/sulfa may be initiated.
Also if inflammation is noted an NSAID such as meloxicam may be given.

For information regarding medications refer to the Rat Medication Guide.

Nursing Care

• Check the penis on daily basis and gently remove plug as needed.
• Provide extra fluids to encourage hydration.
• Provide a healthy diet which includes block food containing a reduced percent of protein.

Outcome

• Inflammation of urethra prevented
• Blockage of urine flow prevented
• Infection of urinary tract prevented

Prevention

• While there is no prevention to the formation of proteinaceous plugs, assisting the elderly or ill rat by gently removing these plugs can help to prevent inflammation to the urethra, as well as, infection and discomfort.

References

1. Bennett, R. A. (2012). Soft Tissue Surgery. In K.E. Quesenberry & J.W. Carpenter (Eds.), Ferrets, Rabbits, and Rodents, Clinical Medicine and Surgery (Third Edition ed.) (pp. 378). St. Louis: Saunders.
2. Lejnieks, D. (2007). Urethral Plug in a Rat (Rattus norvegicus). Journal of Exotic Pet Medicine, 16(3), 183-185, DOI: 10.1053/j.jepm.2007.06.007.
3. Mohr, U., Dungworth, D., & Capen, C. (1992). Nonneoplastic and Neoplastic Lesions of the Urinary Bladder, Ureter, and Renal Pelvis. Pathobiology of the aging rat, volume 1 (p. 262). Washington, D.C.: International Life Sciences Institute.