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The Guelph System for Transcervical AI (GST-AI)
Copy of AI Manual for the Guelph System for Transcervical AI
The GST-AI was developed in the late 1980's by researchers at the University of Guelph and the Ontario Ministry of Agriculture, Food and Rural Affairs. It was the first system that demonstrated, under practical conditions, that the cervix of most ewes could be penetrated successfully, and that pregnancies could be established after depositing reasonable doses of frozen semen. Since that time, much has been learned about the benefits and limitations of the system. It has been used in most sheep producing countries on many breeds and in a variety of conditions.
The cervix
of the ewe is longer and more
complex than other domesticated ruminants (cattle, goats, farmed deer). It is
approximately 8 to 10 cm in length and contains 6 or 7 offset rings that make passage of
AI equipment extremely difficult and even dangerous. An extensive study of the cervix
was part of a MSc project of Dr. Gary Halbert, University of Guelph. The
study demonstrated the complexity and the anatomy of the av
erage canal from ewes from a variety of
breeds and reproductive stages. The top photo shows the cervix cut open to demonstrate the
rings. The smaller photo (left) of a latex mold made inside the cervical canal and shows
the mixture of tight narrows and the open cul-de-sacs that can be found around each
opening. Using the information from the study, instrumentation was designed to assist with
cervical passage. The most satisfactory instrument was na
rrow, reasonably
rigid and had an offset end, to assist with passage into the offset rings.
That became the design for the insemination tip seen below and attached to the
modified Cassou AI gun, designed for handling semen in straws.
The most challenging part of
the technique proved to be the entry into the first cervical ring. If that could be
accomplished, then passage could b
e made in most cases. By grasping the tissues around the opening with
surgical forceps, it was found that penetration could be greatly assisted. We soon
learned that an experienced inseminator could learn where to grasp the tissues to increase
the chances of success. Typical os presentations, as seen in the photo at right, suggest
where to grasp to the experienced inseminator.
Of great importance was the positioning of the ewe. Our studies found that positioning on their back with the head tilted down and the hind legs drawn forward greatly improved the success of cervical grasping and penetration. A Poldenvale Foot Trimming cradle proved to be ideal. The Sydell system also works well.
Results from Breeding trials
Results from trials using the GST-AI are reasonably consistent. Overall, an inseminator with some experience, can successfully penetrate the cervix of about 75 % of ewes presented. That penetration rate is affected by may factors:
 | previous pregnancy - maiden ewes are difficult to pass the speculum and to penetrate the cervix |
| period since last lambing - ewes on accelerated breeding systems are considerably easier to penetrate |
| number of lambings - ewes with multiple lambings are easier |
| and maybe breed. |
Some ewes are easy, some are difficult. Inseminators that are overly aggressive can puncture the cervix of the difficult ewe. By trying to penetrate all ewes, the risk is great that some punctures will occur. Generally, nothing bad happens, but the ewe doesn't get pregnant. A study at the Scottish Agricultural College, in Edinburgh, showed infection occurred in some ewes and that they failed to rebreed, likely as a result of infected equipment or previously infected ewes. Another group, laparoscopically inseminated, also had failed pregnancies. No other studies have shown any negative affects on future fertility. It is not recommended to persist in attempts to penetrate the cervix of the difficult ewe beyond a few minutes.
Pregnancy and lambing results tend to be similar to those experienced in the cattle and goat industries when semen is deposited into the body of the uterus. About 50% of those successfully penetrated and inseminated will lamb in well managed programs. In other words, about half of the 75% attempted or between 30 and 40 % of the entire group. There are many factors that have been shown to affect the lambing rate:
| Ewe condition |
| Period since last lambing |
| Ewe stress |
| Ewe diet |
| Semen dose - at least 100million sperm are required |
| Semen quality |
| Semen quantity - enough fluid (use 1/2 cc straws not 1/4 cc) is required to insure that adequate number of sperm cells are carried into the uterus |
| Semen handling - semen is often poorly handled during thawing in on-farm AI programs |
| Season may have an affect |
| Inseminator experience |
Ewe positioned in the Poldenvale Foot Trimming Cradle. Plexiglas vaginal speculum inserted into the vagina with light source attached.
Grasping forceps being introduced into speculum to grasp tissue at opening of cervical canal.
Modified Cassou gun with insemination tip attached being introduced into the stabilized cervix. the grasping forceps being retracted and moved sideways through the slot in the speculum. Speculum and forceps held by right hand.