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Stud work & AI

A particular interest of Agnew Equine is the breeding of mares using AI techniques. The practice is on the BEVA list of practices approved for the insemination of mares with chilled and fresh semen. The advantages of artificial breeding techniques to mare owners include a greater choice of stallions and the ability to keep your mare at home. As a rule, fresh and chilled semen are suited to a broader spectrum of mares and results in better pregnancy rates than frozen semen.

In order for a mare to become pregnant, semen must be introduced into the mare’s uterus at the correct time- the time of ovulation. Ovulation occurs at the end of the mare’s oestrus period, the time when she is sexually receptive and showing signs of being in season. The optimal time to inseminate a mare using fresh or chilled semen is 24 hrs before she ovulates. This allows the semen time to mature within the mare’s uterus maximizing its ability to fertilize the mare’s egg successfully.

studThe timing of insemination in AI programmes is therefore very important. In order to predict the time of ovulation and synchronise this with insemination we use ultrasound scanning. Ultrasonography enables us to detect changes in the mare’s ovaries and uterus that helps us to predict the time of ovulation. Ultrasonography is via the mare’s rectum and is generally well tolerated. The degree of restraint required is very dependent on the mare’s temperament. We can also administer drugs to the mare that encourage her to ovulate when we want her to.

Following a successful insemination mares are routinely scanned 24 to 48 hrs later. This is to confirm that the mare has ovulated and to detect any fluid within the uterus. Fluid accumulates within the uterus in some mares following insemination (termed post breeding endometritis) and if left untreated would impede the ability of the pregnancy to develop. If present, free uterine fluid is treated with an antibiotic washout and drugs that cause the uterus to contract expelling any fluid.

It is worth remembering that mares are not machines and that even with use of modern scanning techniques and drugs they do not always ovulate when we want them to. If the mare has not ovulated at the correct time repeat insemination would be required.

Following a successful insemination, mares are scanned to tell if they are pregnant. It is very important that only single pregnancies are allowed to develop to full term. Twin pregnancies are bad news in mares, and generally result in the death of both foals.

The timing and number of pregnancy scans is a compromise between what is best and what is practical in economic terms. Twins are to be avoided in mares and are best treated early (day 14-16 days). But, early pregnancies are small in size and susceptible to embryonic loss. This means that if mares are scanned early they should be re scanned at a later date to check the embryo is developing normally. By about 26 days a foetal heart beat can be detected on ultrasound, at this stage the embryo is less susceptible to embryonic loss.

If a mare is only able to be scanned once for pregnancy then this should be around day 28 when an embryo with a heart beat should be visible. But, if twins are detected at this stage treatment can be difficult. Ideally mares should be scanned at 16 days and 28 days as this optimises the identification and successful treatment twins and allows the development of the embryo to be monitored.