IT is thought that artificial insemination (AI) first began with the Arabs many years BC but the first recorded incident was in 1322, when an Arab sheikh stole semen from a rival’s stallion!

It wasn’t until 1902 in Denmark that the idea of AI as a method of breed improvement took hold. At that time, breeders in the US and Britain were slower to adopt AI practices than their continental counterparts, instead following the lead of thoroughbred breeders of the day.

The real push to develop AI in the horse came from the Russian Royal Stud in 1909 but the thoroughbred studbook still steadfastly refuses to adopt AI in its own breeding practices.

Nowadays mare owners can choose a stallion who stands anywhere in the world or even a stallion who is dead for several years, and breed their mare with that stallion in their own country and even county. AI has made this a reality and the uptake of AI services is growing rapidly within the Irish sport horse industry, while on the continent, many studbooks report that up to 100% of breedings occur via AI.

There are many ways in which stallion semen can be processed and there is no single method that suits every stallion best. When a stallion is collected for AI, his semen can ultimately follow one of three routes: fresh, chilled or frozen semen processing.

CHILLED SEMEN

The stallion’s semen is usually collected with the use of a breeding dummy and an artificial vagina (AV). The collected semen is carefully handled, assessed and processed and a chilled semen insemination dose is usually 10-25mls, but this can vary.

Chilled semen is best stored at five degrees Celsius at all times and should be deposited into the mare within 12-36 hours after collection. This allows enough time for semen to be collected and delivered to the mare within Europe within a suitable timeframe for success.

Chilled semen is often the preferred choice for mares who are difficult to get in foal and/or older mares. Oftentimes with chilled semen it is also possible to have the semen collected on the morning you need it and provisions can be made for an alternative processing technique which will allow your mare the best opportunity to go in foal.

There are many factors to consider when considering an overall per cycle pregnancy rate; the semen quality, mare and vet all have a role to play. One can expect a per cycle pregnancy rate of approximately 70% with chilled semen, however with experience this percentage can be significantly increased.

FROZEN SEMEN

For frozen semen, stallions are collected in the same way as in the production of chilled semen, although they will typically be collected outside of the breeding season when the semen is more suited to the freezing process.

The semen undergoes laboratory assessment and processes and is ultimately frozen in liquid nitrogen (-196 degrees Celsius) in 0.5ml straws (or less often in 5ml macro straws).

Frozen semen, when handled and maintained correctly, can remain viable for years and so it in this way that we can produce foals from stallions even after their demise.

There is great variability in the quality of frozen stallion semen and this is down to not only the production and handling of the semen in the first instance but also individual stallion variation.

Although the number of progressively motile sperm is not a guarantee of conception, it is one of the most commonly quoted indicators of semen performance outside of the pregnancy rate. In the case of frozen semen, the ‘post-thaw’ progressive motility is the parameter considered and the most common minimum standard is > 35% progressively motile sperm (PMS).

Progressively motile sperm are sperm which are moving in a straight line when viewed under the microscope. Essentially, these are the sperm capable of fertilisation.

Frozen semen with a post-thaw PMS percentage of 40 or higher is considered to be good. Similar to chilled semen, an insemination dose exceeding 250 million PMS post-thaw is likely to optimise fertility.

Low dose insemination techniques allow for fewer sperm to be used, but these techniques are not suited to all stallions’ semen. It is important to remember that using a straw number less than is recommended can reduce your chances of your mare conceiving, depending on the stallion.

Some stallions’ frozen semen is produced with a single straw insemination technique in mind, whereas others are not. It is very important to know the quality of the frozen semen before attempting to split recommended doses.

There is a common belief that chilled semen has a higher fertility than frozen-thawed semen (omitting individual stallion variation), however there are very few studies in this area. There are several studies which clearly show that seasonal and per cycle pregnancy rates are comparable between chilled and frozen semen. However, individual stallion and mare variation must always be considered in order to achieve the best possible outcome.

Emma-Rose Conroy is a veterinary surgeon and the owner of Euro Stallions (Ireland) Ltd, an EU-approved semen storage centre and stallion semen agency in Co Offaly. Mare owners can sign up online at www.eurostallions.ie for monthly newsletters with detailed advice and breeding tips throughout the season