or retract the testicle signifies adequate analgesia. The duration of the internal pudendal nerve block lasts two to four hours [10].
Figure 17.7 Injection of 2 ml local anesthetic in the skin at the ischiorectal fossa.
Figure 17.8 Needle placement for pudendal nerve block.
Source: Image courtesy of Douglas Hostetler.
Figure 17.9 Pudendal nerve block.
Desensitization of the Dorsal Nerve of the Penis
The dorsal nerve of the penis may be desensitized at a location just proximal to the surgical site. With the bull restrained, the penis should be manually extended and a towel clamp should then be placed under the dorsal apical ligament. Alternatively, a gauze tourniquet may be placed around the free portion of the penis to aid in penile extension. With the dorsal aspect of the penis thoroughly cleansed, 2–4 ml of 2% lidocaine hydrochloride should be infused subcutaneously across the dorsum of the penis proximal to the lesion [9].
Alternatively, the dorsal nerve of the penis may be desensitized as it passes over the ischial arch for penile anesthesia and relaxation. The skin associated with the penile body and located 10 cm ventral to the anus and 2.5 cm from midline is infiltrated with 2–4 ml of 2% lidocaine hydrochloride using a small‐gauge needle (22–25 gauge). A 20‐gauge, 4‐cm needle is then inserted through the desensitized skin and advanced for 5–7 cm to contact the pelvic floor. Aspiration ensures that the needle is not in the dorsal artery of the penis. The needle is then withdrawn approximately 1 cm and the area infiltrated with 20–30 ml of 2% lidocaine hydrochloride. The procedure is repeated on the opposite side of the penis. Analgesia and paralysis of the penis will occur within 20 minutes and should last for one to two hours [1].
Anesthesia for Castration
Castration of bulls is a very common surgical procedure in general practice. Historically, castration was often performed with minimal or no anesthesia. However, anesthesia for castration is more commonly practiced because calves benefit from anesthesia with improved feed consumption and rate of gain. Depending on the age and size of the animal, the surgery is usually performed with chemical and/or regional anesthesia (scrotum and testicles). Depending on the size of the calf, the proposed line of incision for removal of the distal aspect of the scrotum should be subcutaneously infiltrated with 5–10 ml of 2% lidocaine hydrochloride. In bulls, an 18‐gauge, 3.8‐cm needle is inserted at an angle (30–45°) into the center of the testicle and 10–15 ml of local anesthetic per 200 kg body weight is injected into the parenchyma of each testicle. The anesthetic quickly enters the lymphatics and desensitizes the sensory fibers in the spermatic cord. For smaller animals or calves, a smaller needle (20 gauge, 2.5 cm) may be used to administer 2–10 ml of 2% lidocaine hydrochloride [1].
References
1 1 Skarda, R. (2007). Local and regional anesthetic techniques: ruminants and swine. In: Lumb and Jones’ Veterinary Anesthesia and Analgesia, 4e (eds. W.D. Tranquilli, J.C. Thurmon and K.A. Grimm), 731–746. Oxford: Wiley Blackwell.
2 2 Skarda, R. (1986). Techniques of local analgesia in ruminants and swine. Vet. Clin. North Am. Food Anim. Pract. 2: 621–663.
3 3 Edwards, B. (2001). Regional anesthesia techniques in cattle. In Pract. 23: 142–149.
4 4 Anderson, D. and Edmondson, M. (2013). Prevention and management of surgical pain in cattle. Vet. Clin. North Am. Food Anim. Pract. 29: 157–184.
5 5 Noordsy, J. and Ames, N. (2006). Local and regional anesthesia. In: Food Animal Surgery, 4e (eds. J. Noordsy and N. Ames), 21–42. Yardley, PA: Veterinary Learning Systems.
6 6 Noordsy, J. and Ames, N. (2006). Epidural anesthesia. In: Food Animal Surgery, 4e (eds. J. Noordsy and N. Ames), 43–55. Yardley, PA: Veterinary Learning Systems.
7 7 Meyer, H., Starke, A., Kehler, W. et al. (2007). High caudal epidural anaesthesia with local anaesthetics or alpha‐2 agonists in calves. J. Vet. Med. A Physiol. Pathol. Clin. Med. 54: 384–389.
8 8 Navarre C. (2006). Numbing: nose to tail. Proceedings from the 39th Annual Convention of the American Association of Bovine Practitioners, pp. 53–55.
9 9 Wolfe, D., Beckett, S., and Carson, R. (1998). Acquired conditions of the penis and prepuce. In: Large Animal Urogenital Surgery, 2e (eds. D.F. Wolfe and H.D. Moll), 237–272. Baltimore: Williams and Wilkins.
10 10 Hopper, R., King, H., Walters, K., and Christiansen, D. (2012). Management of urogenital surgery and disease in the bull: the scrotum and its contents. Clin. Theriogenology 4: 332–338.
11 11 Larson, L. (1953). The internal pudendal (pudic) nerve block. J. Am. Vet. Med. Assoc. 123: 18–27.
18 Surgery of the Scrotum and its Contents
E. Heath King
Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA
Introduction
The scrotum of the bull is a dependent appendage of the ventral abdominal skin that supports and protects the testicles and helps regulate testicular temperature. The testis must be maintained at a temperature 4–6 °C cooler than body temperature for normal spermatogenesis to occur. Testicular thermoregulation is a complex process that involves a combination of evaporative cooling from scrotal sweat glands, relaxation and contracture of the tunica dartos muscle in response to scrotal temperature, and counter‐current heat exchange between the pampiniform plexus and the testicular artery [1]. Trauma, inflammation, or swelling of the scrotum or testes can easily impair testicular thermoregulation, and studies utilizing scrotal insulations have shown that morphological abnormal sperm are produced within 6–14 days of the insult [2].
Physical Examination of the Scrotum and Testicles
Carefully examine the scrotum for dermatitis, edema, scar tissue, and symmetry [3]. Palpate the testicles for relative size, firmness, symmetry, evidence of pain or swelling, presence of fluid in the vaginal cavity, and the ability of the testicles to move freely within the vaginal cavity. There should be no more than 10% difference in the size of the testes and normal testicular tone approximates that of liver.
Ultrasound of the Testicles
Diagnosis of scrotal or testicular disease may be aided by B‐mode real‐time ultrasound using a 5‐MHz probe. Normal testicles are homogeneous and moderately echogenic [4] (Figure
