Teaser animals

Teaser animals are useful to improve herd reproduction (see the ram effect). The Ram effect is a powerful natural phenomenon that utilizes the effects of male pheromones on non cycling ewes. These potent pheromones are secreted in the wool wax of both Rams and Teasers. When a female sheep smells these pheromones it produces an immediate hormonal response. Within hours the hormones that are responsible for the estrus will be increasing in the sheep blood. As a result, almost all the ewes in the flock will ovulate within a few days of introducing the males. The ram effect will only work if the ewes are not exposed to the sight, sound and smell of a ram for a minimum of 21 days prior to teasers being introduced.  Having males with testosterone around improves cycling, fertility and heat detection. Teaser animals should be amenable to handling, not so large that they injure the females, and must be interested in their jobs.

Malone ppt review- youtube

In teaser animals there are two main goals:

• 1. Prevent pregnancy
  • Teaser animals are not destined to sire offspring
  • If offspring are needed, no need to create a teaser animal
• 2. Prevent intromission
  • This is to minimize disease transmission

Pregnancy prevention

We have two main options. For both, the goal is removal of a portion of the sperm pathway. Both affect the same path, just different parts.

Vasectomy

• • Definition: Removal of a segment of the ductus deferens (note ductus deferens= vas deferens) to render a male animal infertile. Vasectomy achieves infertility but does not alter the ability or desire of males to mate; it is best to combine a vasectomy with a procedure that precludes mating to prevent the spread of infectious agents if the animal is part of an open herd.
  • Procedure: The animal is standing, in lateral recumbency, or in sitting position (rams).  A local block is administered.  The incision is at the neck of the scrotum- can be cranially, caudally, or laterally.  Alternatively, both spermatic cords can be reached via an incision over the median raphe.  The skin and parietal layer of the vaginal tunic are incised vertically.  The ductus deferens is located and isolated.  2-3cm of the ductus deferens is removed after ligatures have been placed on each end to prevent sperm leakage.  To ensure the ductus deferens was removed, histopathology can be submitted. If the arteries and veins in the cord are damaged, hemorrhage can occur.  Careful dissection is important.  The skin is closed routinely. See – How to- Vasectomy chapter in ebook.
  • A vasectomized animal should be permanently identified (tatoo, ear notch etc).  Vasectomy can be more challenging compared to epididymectomy. Depending upon the age of the animal, the ductus deferens can be very thin, hard to find and can resemble the ilioinguinal nerve. Transecting the nerve does not prevent pregnancy. However, vasectomy may be easier than epididymectomy if the procedure is performed laparoscopically (camelids) or in adult sheep (due to the restraint position of cradling them on their hindquarters).  A centimeter or longer chunk of the vas deferens should be removed to minimize the risk of recanalization.

Ductus deferens isolated with Allis forceps. From Fubini et al. Farm Animal Surgery.

Chapter 16 – Surgery of the Bovine Reproductive System and Urinary Tract 2017)

Epididymectomy

• • Definition: A surgical procedure to removal all of or part of the epididymis.  This method is the main procedure used to produce teaser animals.
  • Procedure: The animal is standing or placed in lateral recumbency.  Local anesthesia is placed at the ventral scrotum.  A 2cm skin incision in the ventral scrotum is extended into the tail of the epididymis.  The tail of the epididymis is separated carefully from the distal aspect of the testis with blunt dissection, ligated, and removed.  Care must be taken to avoid injury to the testis which will bleed profusely if inadvertently incised.  The skin is closed routinely. See how to- epididymectomy in ebook. 
  • Epididymectomy should be performed 30 days before intended use of the teaser to allow sufficient time to achieve infertility.

Vasectomy vs Epididymectomy

• Both procedures are effective to disrupt sperm pathway.
• Compared to vasectomy, an epididymectomy is a simpler procedure to perform, faster, and has reduced complication rates.  There is a decreased risk of cutting nerves but a higher risk of hemorrhage.  However, a sperm granuloma may form after an epididymectomy.
•  Ultimately, the procedure selected is surgeon preference.

Prevent intromission

Particularly in open herds (herds with new animals coming in), teaser animals should not actually breed the females as this can increase the risk of venereal disease transmission. In order to prevent this, several options exist with varying success rates and healing times.

Penile translocation – aka Sidewinders

• The preputial opening is moved to the flank of the bull. The penis is left untouched. When the bull gets an erection, the penis is extruded out his flank and he usually misses the target. Since there is no pain involved, most of these bulls maintain their libido.
• This procedure requires general anesthesia. It is typically performed in hospitals rather than in the field.
• Healing time is 2 months (plan ahead).
  

  Preputial pouch

• The preputial opening is sutured closed and another opening created ventrally for urine flow. The penis is left untouched. As long as the urine hole is small enough, the penis cannot be extruded. Since there is no pain involved, most of these bulls maintain their libido.
• This procedure requires general anesthesia; however, it is simpler to perform than the penile translocation.
• Urine collects in the sheath requiring periodic flushing (higher maintenance).
• Healing time is 2 months (plan ahead)
  

   Penectomy

• The penis is shortened to prevent intromission.
• Hemorrhage is a risk with this procedure. Careful closure of the corpus cavernosum is required.
• Bulls do not maintain their libido due to apparent discomfort.
• Healing time is 2 months.
  

  Artificial thrombus model

• Methylmethacrylate (mixture of powder and liquid which cures into a solid form) is injected into the corpus cavernosum to prevent erection due to blockage of blood flow.
• The procedure can be performed in the standing animal and is relatively straight forward
• If the urethra is injected instead of the corpus cavernosum, the resultant urinary obstruction can be fatal.
• Healing time is 2 weeks.
  

  Penis tie-down

• Adhesions are created between the penis and the internal sheath, preventing exteriorization of the penis.
• The procedure is relatively quick and straight forward
• Adhesions may break down if the bull gets an erection prior to strong scar tissue formation
• Healing time is 2 months.
  

  Iatrogenic preputial stenosis

• The internal prepuce is wrapped with a K wire (Kirschner wire) to prevent exteriorization of the penis while still permitting urine flow
• Creating the appropriate diameter to keep the penis in place is a bit of an art
• The procedure is quick and straight forward
• Healing time is 2 weeks

Resources

Surgical techniques for the preparation of teaser bulls, 1995 VCNA – older but one of my favs for images and descriptions

Development of Teaser Bulls Under Field Conditions, 2008 VCNA- useful images and explanations

Occlusion of the corpus cavernosum penis in bulls intended for estrus detection: 18 cases (2002–2016), 2019 JAVMA- latest and greatest on this technique; includes challenges and success rates (pdf download link)