Spiral penile deviation
Keywords: penis, bovine, corkscrew, anatomy, infertilityThis image shows severe spiral ("corkscrew") deviation of the penis of a three year Polled Limousin bull. As is typical, the bull had produced calves from his first breeding season but during his third year of life and second breeding season, the owner had observed spiral deviation during the bull's attempts to breed.
The image was taken during stimulation with an electroejaculator. Pre-ejaculate accessory fluid can be seen dripping from the penis.
Notes:
Under certain conditions spiral deviation can be considered normal; about half of the bulls in one study (where a transparent artificial vagina was used) showed slight to pronounced spiral deviation during ejaculation. However, the problem arises when pronounced spiral deviation occurs before penetration, preventing penetration itself. The incidence of that situation varies considerably, but in a large study in New Zealand, just over 10% of the tested bulls showed this problem. It is interesting and potentially important to note that there have been at least two independent observation (one Australian and the other North American) where spiral deviation was more common in polled than horned bulls. This suggests that the condition has a heritable nature; something to bear in mind when considering corrective surgery.
One may ask why it is that even normal bovine penises have a tendency to spiral when fully erect. After reading Ashdown and Smith's paper, the author dissected the terminal portion of a bulls penis to assess its peculiar anatomy first-hand. The image below is the product of that dissection, some 31 years ago! It has been sharpened and annotated for clarification. The anatomy of the bovine penis is not symmetrical. The apical ligament widens out distally from its origin, about 20 cm proximal from the glans. Strangely, it is attached firmly to the left side of the corpus cavernosum but on the right, its attachment could be described as "flimsy". Ashdown had a more elegant description and also described an asymmetric arrangement of collagen fibers in the tunica albuginea of the corpus cavernosum itself.
Image size: 1478 x 971 px
In the image of the author's dissection, the dotted green line (A) indicates the firm and thick attachment of the apical ligament to the tunica albuginea on its left side. The dashed black line (B) marks the approximate dorsal center line of the penis. The apical ligament itself (C) is shaded green. The thin and rather flimsy attachment of the apical ligament to the tunica albuginea on its right side is marked by the red dotted line (D).
During erection, the blood pressure in the corpus cavernosum penis increases to about 200 kPa or (~30psi, close to the pressure in a car tire) or higher, expanding it distally. As the corpus cavernosum expands maximally, it pushes against the thin and loosely attached right side of the dorsal ligament. This allows the corpus cavernosum to "break away" and move sideways and distally from the sturdy, linear attachment of the ligament on the left side. That part of the ligament therefore provides an axis for a spiral deviation to form. This is further explained in the diagram below.
Image size: 1312 x 1483 px
As mentioned, some degree of spiraling is normal but when the right-sided attachment between the corpus cavernosus and the dorsal ligament is stretched beyond its normal limits, the penis begins to spiral prematurely, preventing penetration.
Several surgical approaches have been described to treat excessive, premature spiraling. One of these (braiding of the dorsal ligament) aims to strengthen the attachment between the apical ligament and the dorsal section of the tunica albuginea through fibrous tissue formation. Autogenous transplants of fascia lata to this area have the same outcome but introduce additional tissue strength as well. Carbon fiber implants merely strengthen the dorsal and right side of the area of attachment between the apical ligament and the tunica albuginea. Although success (return to breeding) has been reported with all methods, they have not been compared in controlled studies. Also, the rate of relapse has not been well documented. Because the potentially heritable nature of spiral deviation (recessive, dominance or penetrance) it is probably prudent to avoid surgery in these cases.
References:
Anderson, D.E. 2008. Surgery of the Prepuce and Penis. Vet. Clin. North America: Food Animal Practice. 24: 245-251
Ashdown, R.R. and Smith, J.A. 1969.The anatomy of the corpus cavernosum penis of the bull
and its relationship to spiral deviation of the penis. J. Anat. 104:153-159
Becket, S.D et al 1974. Corpus cavernosum penis pressure and penile muscle activity in the bull during coitus. Am. J. Vet. Research 35: 761-764
Lewis, J.E. et al. 1968. Blood pressure within the corpus cavernosum penis of the bull. J.Reprod. Fert. 17:155-156
McDiarmid, J.J. 1981 "Corkscrew penis" and other breeding abnormalities in beef bulls
N. Zealand. Vet. J. 29:35-36
Mobini, S. 1982. An experimental evaluation of the response of the bull penis to carbon fiber implants Cornell Vet. 72:350-360
Pearson, H. 1974. Corkscrew penis: relapse in a bull after surgical correction, Corkscrew penis: relapse in a bull after surgical correction. Vet. Record. 94:225
Seidel, G.E. and Foote, R.H. 1969 Motion picture analysis of ejaculation in the bull. J. Reprod. Fert. 20: 313-317
Whitsell, D. 1969. Deviations of the bovine penis Iowa State University Veterinarian. 31. Article 5. 25-28.
