Fertilisation facts

PART 1

TEXT: GEORGIA HARLEY

With the pitter-patter of tiny hooves all over South Africa at the moment, many of us suddenly develop a curiosity about the breeding process. It might be wanting to sound clued up on all the acronyms or the difference between chilled and frozen semen, or perhaps (more likely) it's just seeing all the adorable foal pictures littered across social media, but whatever the reason, we want to know more. The good news is that Team HQ, struck by the same insatiable curiosity, have done the research for you and, over the next few issues, will be telling you EVERYTHING you need to know to demystify the breeding process. To start, we will look at the various fertilisation methods employed to create our day-zero developing foal. In this particular article, we focus specifically on live coverings and artificial insemination (AI), and next time, we will be back to consider the roles of intracytoplasmic sperm injection (ICSI), ovum pickup and embryo transfer.

PRE-BREEDING CHECK

Before breeding with your mare, it is advised to have a pre-breeding check performed. This is to ensure that the mare is healthy and that no factors decrease the chance of falling pregnant or make a successful pregnancy unlikely. The main components of this prebreeding check include the following:

• An ultrasound scan of the uterus

• A vaginal examination to assess the conformation of the vulva and look for any cervical abnormalities.

• A uterine swab and smear to check for any infections.

LIVE COVERING TECHNIQUE

As the name suggests, live covering is when the mare and stallion physically mate together. There are two types of live covering: pasture breeding and hand or in-hand breeding. The difference between the two is simple. With pasture breeding, the mare and stallion are put together and breed as they choose. Although this is undoubtedly the most natural, it is also the most dangerous breeding method for both stallion and mare.

Many stallions and some mares become aggressive when breeding, and a single kick from either partner can break legs and end life. An added disadvantage is that this natural method does not always have a high success rate, as, left unsupervised, the two equines can struggle to get all the right parts into the right places.

In-hand breeding, on the other hand, requires the stallion and mare to be held and will take place in a controlled environment. The breeder will see when his mare is in heat, and then a few days after her heat starts, he will begin the covering process. Covering will then happen every day or two until the mare is no longer in heat. This is a safer alternative to pasture breeding and allows for some human intervention where needed.

ADVANTAGES AND DISADVANTAGES

The main advantage of either form of live covering is that the semen can live for up to four days when placed in the mare in this natural way. This means the covering does not have to be absolutely in time with the mare's ovulation. The main disadvantages of these methods are the level of risk for the stallion and mare, as mentioned above, the lack of confirmation of whether the stallion has indeed ejaculated and the unpredictable success rates.

However, for certain breeds of horses, like the Thoroughbred, live covering is compulsory. This is because the Thoroughbred Studbook feels that Artificial Insemination (AI) dilutes the gene pool by allowing inferior mares to access top-quality semen.

ARTIFICIAL INSEMINATION (AI)

Artificial insemination, or AI, is a technique used to transfer appropriately processed semen from a selected stallion into the mare's uterus at the correct stage of the oestrus cycle, resulting in a single pregnancy.

TECHNIQUE

AI is performed using one of these three types of semen:

1. Fresh semen: This semen is used primarily at studs as it only lasts for short periods once collected from the stallion.

2. Chilled semen: Chilled semen is stored at 4 degrees Celsius in either a special container or polystyrene container with a chill/ice pack inside. Chilled semen must be used within 48 hours of collection.

3. Frozen semen: Frozen semen is frozen in nitrogen at -196 degrees Celsius. You can keep frozen semen for as long as needed and thaw it when you are ready to use it.

The success of the AI program depends on several factors like the quality of the semen from the stallion, the fertility status of the mare and the program employed by the attending vet. Conception rates with fresh and chilled semen are similar to or slightly better than with live covering, with approximately 60% of all mares becoming pregnant on the first cycle. Until recently, conception rates with frozen semen were less favourable, but as experience has grown with the techniques, this situation is improving.

The key element of the program employed by the attending vet is the timing, as the success of the insemination depends hugely on when the semen enters the uterus. Therefore, the semen should be placed when the mare is in season and close to ovulation. Most mares will have a 21–22 day cycle, with oestrus lasting 3-6 days.

Performing AI with fresh or chilled semen: Usually, a mare will be scanned just before she is expected to start her season, and during this scan, the attending vet will check the size of the developing follicles. This will help determine when to have the semen ready and when to give the ovulation-inducing agent. If it is impossible to predict when the mare will come into season, she is given medication to bring her into the season. Insemination should take place at the time of the ovulation of the largest follicle. The mare will be scanned the day after AI to ensure ovulation has taken place and that there is no fluid build-up in the uterus.

Straws of frozen semen

Performing AI with frozen semen AI: Using frozen semen does have a lower success rate than with fresh or chilled semen, but success rates are increasing all of the time. Using frozen semen is also more expensive for the breeder; this is because the process of freezing and storing the semen, and thawing it for use is more timeconsuming and labour-intensive, and a vet will need to be on hand to scan more regularly. With frozen semen, the mare will be scanned every six hours to plan the insemination for the exact moment that ovulation takes place. Again, the mare will be scanned the day after AI to check that there is no fluid build-up in the uterus.

The use of AI has many potential advantages over live covering:

• It allows the use of semen from stallions that would not normally be accessible, such as from competing sport horse stallions, international stallions and even deceased stallions.

• It avoids large amounts of travelling on the part of the mare or stallion.

• There is a much lower risk of injury to the mare and stallion.

• The semen is evaluated at every collection and before it is inseminated, thereby allowing any potential fertility problems to be identified.

• It allows breeders to breed with mares with young foals at foot or mares who do not tolerate a stallion covering them naturally. However, it is definitely a more costly alternative to live coverings due to the high degree of veterinary input required and the elaborate freezing and thawing procedures. It is also not permitted for Thoroughbreds.

COLLECTING SEMEN

For most facilities, collecting semen from a stallion using a phantom or mount mare is the preferred option, as it is an efficient and generally safe process that mimics the natural position assumed by the stallion in live breeding. Ground semen collection is an alternative option where there is no phantom, where the stallion is very small, where the stallion struggles with the phantom or where the stallion has mobility issues due to injury or other health problems. In ground semen collection, an artificial vagina and/or manual stimulation are used.

Next issue we’ll be discussing the roles of ICSI, ovum pick up and embryo transfer. Don’t miss it!