Intracytoplasmic sperm injection (ICSI), a groundbreaking assisted reproduction technique, has revolutionized horse breeding since its inception over two decades ago at Colorado State University. This advanced procedure, initially developed for other species, has become a vital tool for extending the reproductive life of horses, particularly those with genetics that produce champions. ICSI offers a renewed hope for breeders seeking to preserve and propagate valuable bloodlines.
The American Quarter Horse Association (AQHA) has established specific rules to ensure fairness and maintain the integrity of the registry as reproductive technologies evolve. These regulations, detailed in the AQHA Handbook of Rules & Regulations, are crucial for breeders considering ICSI. Before embarking on the ICSI process, owners must ensure that any resulting foals will be eligible for registration. AQHA’s REG112 specifically addresses the registration of horses conceived through embryo/oocyte transfer. Owners are required to notify the AQHA in writing and pay a fee of $200 before attempting to collect a fertilized egg. Mares can be enrolled in the embryo program either for life or on an annual basis. Furthermore, all resulting foals must undergo parentage verification before registration can be completed. A key rule to remember, as per REG111.6, is that semen from stallions foaled in 2015 or later cannot be used more than two years after the stallion’s death or castration. Similarly, for mares born in 2015 and after, stored embryos and oocytes are only viable for use up to two years post-mortem, according to REG112.9.
How ICSI Benefits Mares
While ICSI was initially seen as a solution for older stallions who had become infertile, its benefits extend significantly to extending the breeding life of broodmares. In both scenarios, the mare plays a critical role, as the successful harvesting of a viable oocyte—an immature egg cell—is paramount. Older mares typically have fewer follicles, yielding fewer oocytes and presenting a greater challenge. The aspiration process, which can be performed whether the mare is in season or not, involves guiding a needle through the mare’s flank to the ovary or via ultrasound through the anterior vagina. This procedure requires only a single sperm from the stallion.
Most veterinarians prefer the ultrasound-guided method. A mature oocyte can be collected from the aspirated dominant follicle and must be injected with sperm within a specific timeframe. If the oocyte is to be shipped, it requires a special culture medium and incubator. Immature oocytes are more commonly collected due to their higher numbers and ease of shipping; however, they necessitate incubation and culturing for 24 to 30 hours to reach maturity.
Dr. Glenn Blodgett of the Four Sixes Ranch highlights that oocyte aspiration carries minimal risks, such as hemorrhage or secondary complications, and potentially scarring from repeated ovarian perforations. Consequently, this procedure is generally not recommended for reproductively healthy mares that can conceive normally. Dr. Rob Foss of Equine Medical Services emphasizes the veterinarian’s responsibility to fully inform clients about the procedure’s risks and to employ proper techniques. He notes that while research indicates low risk, precautions like proper restraint, tranquilizers, pain relievers, antibiotics, and sterile conditions are essential. Dr. Foss also advises against using ICSI for young, otherwise healthy mares, but acknowledges that for breeding to stallions where ICSI is the only option, mare owners must weigh the economic factors and risks against the potential value of the foal. Studies have shown that routine follicular aspiration generally does not impact future fertility, even in mares that have undergone multiple aspirations. Potential fertility issues may only arise from infection post-aspiration or accidental puncture of the oviduct. In Dr. Foss’s practice, mare infertility remains the primary reason for performing ICSI, as these mares struggle to produce embryos independently, necessitating laboratory assistance. While an increase in mares seeking ICSI for stallions with poor semen quality or quantity is observed, mare infertility still dominates as the reason for the procedure.
The ICSI Procedure
Leading institutions like Texas A&M and Colorado State Universities offer comprehensive ICSI services. EquiEmbryo in Fort Worth, Texas, was among the first private laboratories to perform the sperm injection itself, alongside services such as embryo freezing, manipulation, warming, genetic testing biopsies, and stallion fertility testing. Dr. Young Ho Choi at EquiEmbryo manages oocytes based on their maturity. Mature oocytes, aspirated from preovulatory follicles, are less common, especially in mares with few follicles. Most oocytes received are immature and require 24 to 36 hours of incubation. During this period, the formation of a polar body signals maturity and readiness for ICSI. Without this, the oocyte degenerates. Typically, about 60% of aspirated oocytes per follicle can develop to the blastocyst stage, a transferable embryo stage.
Dr. Choi outlines the ICSI process as an 11-day procedure involving meticulous steps: medical preparations, oocyte maturation, ICSI, and embryo culture, each demanding high skill and concentration. While predicting success can be challenging, as the same mare or stallion may yield different results, ICSI techniques have significantly improved, increasing success rates. Dr. Choi averages three embryos from every 10 injected oocytes, though production varies greatly among individuals. Oocyte quality, influenced by the mare’s age, nutrition, and overall health, plays a crucial role. The cost of achieving pregnancy via ICSI, ranging from $5,000 to $10,000, is influenced by factors beyond equipment, with laboratory expertise and quality control being critical. A significant advancement has been the ability to culture embryos to the blastocyst stage for non-surgical transfer, a notable improvement over earlier surgical transfers of younger embryos. While frozen semen has long been used to preserve stallion genetics, embryo freezing is also gaining traction. Dr. Foss notes an approximate 10% drop in pregnancy rates with frozen embryos, but they remain effective for transferring flushed embryos from mares aspirated out of season for the following season, or for storing surplus embryos.
How ICSI Benefits Stallions
Age-related infertility in stallions makes collecting and freezing semen a common practice to extend their breeding market presence. The Four Sixes Ranch made headlines by offering breedings through ICSI for renowned Quarter Horse stallions Streakin Six and Special Effort. Special Effort, who passed away in 2006, was a celebrated racer, earning over $1.2 million and siring numerous successful offspring. Streakin Six, a multiple stakes winner who earned $473,934, also sired highly successful progeny. Neither stallion falls under the 2015 restriction for postmortem breeding. Dr. Blodgett noted a limited supply of Streakin Six semen, making ICSI the only viable option. Despite previous unsuccessful attempts with frozen semen from Special Effort, Dr. Rick Beck achieved success using ICSI. Dr. Beck successfully retrieved oocytes from an 18-year-old mare, resulting in pregnancies for both Streakin Six and Special Effort. This demonstrates ICSI’s ability to utilize stallions whose semen quality may not be suitable for traditional methods or to breed with mares who are no longer producing viable embryos.
Stallion owner Brian Ellsworth shared a similar experience when a valuable stallion died, leaving only a small quantity of poor-quality semen. Conventional methods failed, prompting him to seek Dr. Foss’s expertise. Brian views ICSI as a “hail Mary” option in such high-stakes situations, acknowledging the risk-reward calculation involved. He wasn’t concerned about adverse effects on his 11-year-old mare, given her previous successful conventional breedings and champion offspring. Brian emphasizes that ICSI is not for everyone but is a viable option for those with faith in their breeding program and when it’s the only recourse. His first ICSI foal was born in 2018, and he continued the process in subsequent years.
ICSI: An Option Among Many
Veterinarians stress that ICSI should be considered one option among many in a breeder’s arsenal. Dr. Foss cautions that “no one should enter into it lightly,” as the procedure, like any invasive technique, carries rare but possible complications. However, for those facing specific reproductive challenges, ICSI can be instrumental in reviving valuable genetic lines. Dr. Blodgett notes its importance for mares with abnormalities preventing normal conception or older mares unable to conceive naturally, expressing gratitude for its availability.
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