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Basics ⬇

Outline

BASICS

Definition!!navigator!!

ICSI is a method for in vitro fertilization in which a single sperm is injected into the cytoplasm of a mature oocyte to achieve fertilization. The resulting fertilized oocytes are cultured for 7–10 days to allow development into blastocysts, which can then be transferred transcervically into a recipient mare, as for standard embryo transfer.

Advantages of ICSI over OT

  • OT is the surgical transfer of matured oocytes to the oviducts of inseminated recipient mares; ICSI avoids the need for surgery on the recipient mare
  • Fresh, frozen, or cooled semen and semen of low quality can be used to perform ICSI; for OT a dose of good quality semen is needed to inseminate the recipient mare

Pathophysiology!!navigator!!

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Systems Affected!!navigator!!

Reproductive

Genetics!!navigator!!

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Incidence/Prevalence!!navigator!!

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Geographic Distribution!!navigator!!

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Signalment!!navigator!!

  • Oocytes can be recovered from mares of any age, although recovery is more commonly performed in older mares that are unable to carry foals to term or deliver foals themselves or when pregnancies are sought from stallions with limited supplies of spermatozoa
  • Any breed. Owners should consult individual breed registries for guidelines regarding the possibility of registering any resulting foals

Signs!!navigator!!

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Causes!!navigator!!

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Risk Factors!!navigator!!

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Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

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CBC/Biochemistry/Urinalysis!!navigator!!

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Other Laboratory Tests!!navigator!!

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Imaging!!navigator!!

  • Transrectal US to monitor follicular growth and determine timing of hCG administration if aspirating a dominant stimulated follicle
  • Transvaginal US for aspiration of immature follicles via TVA

Other Diagnostic Procedures!!navigator!!

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Pathologic Findings!!navigator!!

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Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Oocyte recovery from live mares is best performed in a hospital setting with adequate facilities for mare restraint and trained personnel experienced in follicular aspirations
  • ICSI is performed at a laboratory equipped with the proper equipment (micromanipulator, incubator, hood, microscope, etc.) by trained personnel knowledgeable in embryo culture medium preparation and experienced in oocyte and embryo handling, sperm preparation, and micromanipulation
  • Ovaries from euthanized mares can be shipped to the ICSI laboratory for oocyte recovery, maturation, and ICSI. Alternatively, the referring veterinarian can recover oocytes from the ovaries and ship the oocytes to the ICSI laboratory for maturation and ICSI

Indications!!navigator!!

  • Subfertile mares that cannot provide embryos for transfer due to chronic endometritis, pyometra, uterine adhesions, cervical tears, persistent anovulatory follicles, oviductal blockage, or idiopathic causes
  • Subfertile stallions with very low sperm numbers or quality
  • When only a few straws of frozen semen exist from deceased stallions
  • When oocytes are recovered from mares’ ovaries after euthanasia

Oocyte Recovery Procedures!!navigator!!

Dominant Stimulated Follicle

  • Must monitor follicular growth; predict the first day of responsiveness as indicated by size, shape, and wall thickness of dominant follicle, and administer hCG or deslorelin
  • Aspirate follicle 24–35 h after hCG administration
  • Can aspirate follicle via flank aspiration

Advantages

  • High recovery rate (>80%)
  • Essentially all recovered oocytes are mature
  • High embryonic developmental competence

Disadvantages

  • Only 1 or 2 follicles/oocytes available per cycle
  • Must accurately time hCG stimulation and aspiration
  • In vivo matured oocytes are sensitive to temperature and difficult to ship

Immature Follicles

  • All follicles ≥5 mm in diameter on the ovary can be aspirated
  • Must aspirate via US-guided TVA

Advantages

  • Many follicles are available for aspiration (average 9 follicles per mare per TVA)
  • Immature oocytes are easy to ship

Disadvantages

  • Lower recovery rates (54% or 5 oocytes per TVA)
  • Lower maturation rates (66% or 3 mature oocytes per TVA)

Postmortem

  • Mare is anesthetized with xylazine/ketamine, ovaries are removed and the mare is euthanized immediately after
  • Best results when oocytes are recovered from ovaries within 6 h of euthanasia
  • If transporting ovaries <2 h, maintain at body temperature (37°C); if transporting >2 h, cool to room temperature (20°C). Do not refrigerate ovaries

Nursing Care!!navigator!!

May be required if complications (see Possible Complications) occur during the procedure.

Activity!!navigator!!

Restricted while the mare is under sedation.

Diet!!navigator!!

Normal diet.

Client Education!!navigator!!

  • Oocyte recovery by flank aspiration or TVA is a relatively benign procedure; however, certain complications (see Possible Complications) can occur
  • Performing ICSI is much more labor intensive and expensive than standard embryo transfer
  • ICSI is a procedure that should only be used when the indications listed above are present, and it is not a recommended means of obtaining more foals in a given season from normally fertile mares using good quality semen

Surgical Considerations!!navigator!!

If an ovarian abscess develops following oocyte recovery, surgery may be indicated to remove the affected ovary.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

For Oocyte Recovery via Flank Aspiration or TVA

  • Detomidine for sedation
  • Butorphanol tartrate for analgesia
  • N-butylscopolamine bromide as an antispasmodic
  • Flunixin meglumine for analgesia; administered after oocyte recovery
  • Antibiotics if complications occur during the procedure

For Oocyte Recovery from Ovaries Postmortem

  • Xylazine/ketamine for anesthesia, and after ovary removal, followed by
  • Pentobarbital or KCl for euthanasia

Contraindications!!navigator!!

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Precautions!!navigator!!

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Possible Interactions!!navigator!!

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Alternative Drugs!!navigator!!

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Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Follicular aspirations of immature or dominant stimulated follicles can be performed once every 2 weeks. If aspirating a dominant stimulated follicle, follicular growth must be monitored by transrectal US.

Prevention/Avoidance!!navigator!!

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Possible Complications!!navigator!!

  • Rectal bleeding
  • Ovarian abscess
  • Peritonitis
  • Death from puncture of uterine artery

Expected Course and Prognosis!!navigator!!

Expected outcomes may vary by laboratory because different laboratories use different procedures and media for the different steps involved with in vitro embryo production. The expected outcomes at the Texas A&M Equine Embryo Laboratory are:

  • 66% of immature oocytes mature in culture
  • 75% of oocytes undergo cleavage after ICSI
  • 23% of oocytes, recovered from immature follicles, subjected to ICSI will develop blastocysts
  • 38% of oocytes, recovered from dominant stimulated follicles, subjected to ICSI will develop blastocysts
  • 52% foaling rate per transferred blastocyst

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Subfertility

Age-Related Factors!!navigator!!

  • For mares ≤24 years of age, age does not affect oocyte recovery rate, blastocyst rate, or pregnancy or foaling rates. However, older mares tend to have fewer follicles and therefore there are fewer oocytes to recover and fewer blastocysts are produced
  • Stallions do have an effect on the cleavage and blastocyst rates after ICSI; embryo development rates may be altered by the method used to prepare sperm prior to ICSI

Zoonotic Potential!!navigator!!

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Pregnancy/Fertility/Breeding!!navigator!!

See Expected Course and Prognosis.

Synonyms!!navigator!!

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Abbreviations!!navigator!!

  • hCG = human chorionic gonadotropin
  • ICSI = intracytoplasmic sperm injection
  • OT = oocyte transfer
  • TVA = transvaginal aspiration
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Brinsko SP, Blanchard TL, Varner DD, et al. Assisted reproductive technology. In: Manual of Equine Reproduction, 3e. St. Louis, MO: Mosby Elsevier, 2011:302–312.

Hinrichs K, Choi YH. Factors influencing the success of equine intracytoplasmic sperm injection in a clinical program. Reprod Fertil Dev 2015;28(2):258.

Hinrichs K, Choi YH, Love CC, et al. Use of intracytoplasmic sperm injection and in vitro culture to the blastocyst stage in a commercial equine assisted reproduction program. J Equine Vet Sci 2014;34:176.

Author(s) ⬆

Author: Sicilia T. Grady

Consulting Editor: Carla L. Carleton