Bovine Reproduction. Группа авторов
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observation. All these methods depend on female cattle standing for mounting during estrus. Thus these methods might miss females with weak or short estrus behavior [1]. By far the most efficient estrus detector is the bull, with the caveat that there is the benefit of male presence [2]. Therefore utilization of a teaser bull (intact sterilized male) is the most reliable method of estrus detection in the utilization of an AI program.
Several factors need to be considered when choosing a teaser bull procedure and each producer will have different needs and expectations. Besides the obvious need to render the bull sterile, other considerations would include herd status (open or closed herd). If an open herd, venereal disease transmission is an important factor to consider and prevention of intromission during mounting will be an important factor when choosing a teaser bull surgical procedure. Additionally, expected longevity needs to be discussed with the producer. On average, teaser bulls will last one to three years within a herd [1]. Decreased libido is the most common reason for culling, with excessive size and aggression being the next most common culling reasons [3]. To summarize, the main goals of surgical preparation of teaser bulls are to render him sterile, prevent intromission and therefore the transmission of venereal disease, and avoid excessive libido reduction [4, 5].
Proper bull selection is also an important aspect of teaser bull preparation. The ideal bull needs to be of moderate size, mild temperament, and easily handled. This bull also needs to be free of transmissible diseases. Of course, the bull also needs strong libido, but this can be difficult to assess in yearling bulls [4]. Teaser bull surgery should be performed well before the breeding season to allot time for healing and recovery from surgery. Ideally, the procedure should be performed on bulls less than 272 kg, primarily for ease of handling and decreased hemorrhage during surgery [4].
Teaser bull procedures can be divided into two categories: those that block semen flow and deliver sterility (vasectomy, epididymectomy) and those that prevent penile penetration (penile–prepuce translocation, penopexy, preputial pouch). Depending on the needs and expectations of the producer, any one or a combination of these procedures can be used for preparation of a teaser bull.
Vasectomy
As previously mentioned, vasectomy will render a bull sterile but does not prevent normal mating and copulation behavior. This procedure can be performed with the bull in standing restraint or recumbency, or a tilt chute may be used if available. The typical surgical approach is an anterior approach on the neck of the scrotum. However, if standing restraint is chosen, then the approach would be the posterior aspect of the neck of the scrotum. Figure 21.1 shows the procedure.
Figure 21.1 Procedure for vasectomy.
Source: Illustration by Mal Hoover.
The neck of the scrotum should be clipped and aseptically prepared for surgery. Lidocaine 2% should be infused over the proposed incision site over each spermatic cord. A 3‐cm incision should be made through the skin and tunica dartos over each spermatic cord. The spermatic cord is isolated by placing a hemostat underneath the entire spermatic cord. The ductus deferens is then identified via palpation. The ductus deferens is a firm structure that runs medially along the spermatic cord and is approximately 2–3 mm in diameter. Once identified, the tunica vaginalis is carefully incised, utilizing extreme caution so as not to damage the cremaster muscle or pampiniform plexus resulting in excessive hemorrhage. After the tunica vaginalis is incised, the ductus deferens is isolated with another hemostat.
Two ligatures are placed approximately 3–5 mm apart using #0 absorbable suture [4, 5]. The ductus deferens is removed between the two ligatures. The skin is closed with a cruciate pattern using nonabsorbable suture. Antibiotics can be administered to prevent any postoperative infection, especially if surgical contamination has occurred. It is recommended to wait 30 days prior to using the bull as a teaser animal, since sperm can be present in the reproductive tract up to 30 days postoperatively [4, 5]. Additionally, it is recommended to perform yearly evaluations of the teaser animal's ejaculate to ensure sterility of the animal.
Epididymectomy
An epididymectomy is similar to a vasectomy with regard to restraint options and copulation behavior [6]. For this procedure, the base of the scrotum is clipped and aseptically prepared. Lidocaine 2% is infused over the tail of the epididymis. Once prepared, the surgeon grasps the neck of the scrotum and pushes the testicle ventrally. A 3‐cm incision is made over the tail of the epididymis through the skin and common vaginal tunic until the epididymis is exteriorized. The tail of the epididymis is carefully dissected from the testicle, and towel clamps or Allis tissue forceps can be used to assist in handling and manipulation of the epididymis. A hemostat is placed on the ductus deferens and the body of the epididymis. Ligatures with #0 absorbable suture are placed proximal to the hemostats. The tail of the epididymis is removed by transection distal to the hemostats. Figure 21.2 shows the procedure.
Figure 21.2 Procedure for epididymectomy.
Source: Illustration by Mal Hoover.
The common vaginal tunic is closed using #0 absorbable suture. The skin can be closed with non‐absorbable cruciate sutures or the incisions can be left open to allow ventral drainage. Antibiotics can be administered to prevent postoperative infections. Postoperative resting recommendations and yearly ejaculate examinations are the same as previously stated for vasectomy aftercare.
Penile–Prepuce Translocation
Penile–prepuce translocation (“sidewinder”) is the surgical transposition of the penis and prepuce from the ventral midline to the right or left flank of a bull. This procedure allows normal protrusion and erection but does not permit intromission. In general, “sidewinders” are preferred by producers due to longevity and herd retention of the teaser animal. Bulls with a penile–prepuce translocation maintain better and longer libido since this procedure allows normal protrusion and does not cause pain during erection. Some bulls are able to compensate and learn how to breed females despite the translocation of the penis and prepuce. Therefore it is recommended that a vasectomy or epididymectomy is performed to ensure sterility of the bull.
Penile–prepuce translocation is performed in lateral recumbency, so general anesthesia is the preferred method of restraint. If general anesthesia is not possible, heavy sedation with rope restraints and local infiltration of 2% lidocaine can be used. Ideally, food should be withheld for 24 hours and water for 12 hours before performing the procedure.
Prior to placing the bull in recumbency, the translocation site for the preputial orifice should be identified. The translocation site should be just outside the flank fold and lateral to the original preputial orifice site [3]. An 18‐gauge needle can be used to abrade the epidermis so the location is not altered after placing the animal in recumbency and skin stretching occurs. The ventral abdomen from the umbilicus to just cranial to the scrotum and the site of translocation of the flank should be clipped and aseptically prepared. Flush the prepuce with dilute iodine solution.
Before making the initial incision, place one simple interrupted suture at the dorsal aspect of the preputial orifice to serve as a marker and prevent twisting of the prepuce during translocation. A circumferential skin incision around the preputial orifice is made 4 cm from the orifice or a total diameter of 8–10 cm (Figure 21.3) [3, 4]. Extend the skin