With the start of the 2018 breeding season approaching, stallion owners are making plans for standing their horses at stud. With the notable exception of Weatherbys (which registers Thoroughbred racehorses), the vast majority of British and international equine stud books now allow the use of artificial insemination (AI).
The advantages of using AI are many; it allows shipment of semen to distant destinations and removes the need to transport stallions or mares and foals for breeding purposes. Use of freshly-collected semen appropriately inseminated using a minimum contamination technique also provides the optimal method of achieving a pregnancy in many sub-fertile mares.
From the stallion owner’s point of view, making the stallion available via shipped chilled or frozen semen opens up national and international markets. Training the stallion to use a dummy mare for semen collection also significantly reduces the risk of injury to the stallion associated with covering live mares or having semen collected using a ‘teaser’ mare. Being able to collect and freeze semen for future use means stallions do not have to combine stud duties with competition during spring and summer.
All the venereal diseases which can be spread by ‘natural cover’ can also be transmitted in semen, and the fact that ejaculates are often split between multiple mares and destinations means that AI is a fantastic way of spreading disease. It is therefore crucial that all stallions being used in an AI programme are tested annually in line with the HBLB Codes of Practice, which specify which diseases stallions should be tested for after 1st January each year, and how the tests should be undertaken.
As specified in the ‘AI’ section of the HBLB Codes, all semen collections should be undertaken using appropriate biosecurity measures, and shipments of semen should be accompanied by the appropriate paperwork certifying freedom from disease. Teaser mares with which the stallion will come into contact must also be tested free of venereal disease, as specified in the HBLB Codes.
Semen collection methods
A physical examination should be carried out to assess any abnormalities (including those of the reproductive tract) which might affect the stallion’s fertility (Varner, 2016). Semen can be collected from stallions for use in AI using a real mare, a ‘dummy’ mare, or ‘ground collection’. If a real mare is being used, she should either be in behavioural oestrus, or be ovariectomised.
Ovariectomised mares have historically been treated with oestrogen to make them display signs of oestrus. There is no oestrogen currently licensed for use in horses in the UK. The use of a real mare exposes both stallion and mare to injury from kicking or biting, and the person collecting the semen is of necessity situated between the two horses.
Collection of semen using ‘ground collection’ (i.e. when the stallion mounts neither a real mare nor a dummy, but is collected while standing on the ground) is useful in some cases of orthopaedic or neurological disease which prevent the stallion from mounting and ejaculating. However, it is not well-tolerated by all stallions and is always relatively dangerous for the semen collector and stallion handler. The rest of this article will concentrate on using a dummy mare for semen collections, which is usually the safest and preferable method.
Using a dummy mare
Dummy mares are commercially available. They should be situated under cover, in an area with adequate space, and with a non-slip, disinfectable flooring. Dummy mares should be disinfected between stallions.
Safety is paramount – everyone involved in the collection process should wear a hard hat, a back protector and shoes that provide protection. Everyone should be aware in advance of where they should go should they become endangered. The stallion should be suitably restrained, e.g. using a Chiffney bridle and long lead rope (not a lunge line), and the stallion handler should be experienced.
The stallion is trained to mount the dummy by placing the teaser mare (usually in oestrus) on the far side of the dummy and allowing the stallion to tease her over the dummy. With patience, the stallion will become aroused
Everyone should be aware in advance of where they should go should they become endangered
and will start to try to reach the mare by jumping onto the dummy. Some stallions become frustrated (and dangerous) during the training process – multiple short training sessions are more rewarding and safer than fewer long sessions. When the stallion has mounted the dummy, the person handling the artificial vagina (AV) moves forward on the left side of the dummy and deflects the stallion’s penis into the AV. The stallion handler should also be on the left side of the dummy (Figure 1).
There are various models of AV available – this author routinely uses the Missouri model (Figures 2 and 3). AVs should be filled so that the lumen is c. 38° C, and lubricated with a non-spermicidal lubricant, wearing a long glove. Novice stallions will not necessarily ejaculate the first time they mount the dummy.
Once the stallion has been trained to use the dummy and the AV successfully, and has ejaculated enough times to be sure that any sperm cells that have accumulated in the deferent duct system have been ‘flushed out’, his semen should be assessed. The detailed description of such assessment is outside the scope of this article (see Baumber-Skaife, 2011).