Tristan Starr, AI Technician, B.Sc.Agr (Hons)

Thirty years ago, artificial breeding was an unfamiliar term reserved only for scientific research. Today, it offers new opportunities and has infinite potential for a broad range of breeders. Artificial technologies are not limited to artificial insemination, in fact, there are a number of versatile artificial breeding techniques to suit the individual needs of breeders and owners.

For many of us involved with breeding horses, the safe delivery and maintenance of a healthy foal are the ultimate goals. Although nature can interfere with this objective, good management practices increase the chances of success. Good management involves both the mare and the stallion and begins well in advance of conception.

Semen Collection, Handling and Evaluation

Every stallion should undergo a breeding soundness exam. The test includes assessing the quality and quantity of semen, as well as the libido and mating of the stallion. This examination could uncover any possible congenital defects or infectious diseases, establishes the number of mares that could be booked to the stallion a breeding season and the extender to be used for AI.
Semen quality is assessed based on the percentage of spermatozoa that is progressively motile and morphologically normal.
Parameters for semen evaluation include:

  • Gross appearance of the sample
  • Volume - gel, gelfree and total seminal volume
  • Motility
  • Concentration of spermatozoa
  • Total spermatozoa numbers
  • Spermatozoa morphology
  • pH of ejaculate

Semen collection is performed with an AV (artificial vagina). All AV components that are exposed to the ejaculate must be non?spermicidal and all equipment to be used in semen collection should be warmed to 380C. At the beginning of the breeding season each stallion should be collected several times to clean out and to determine the conditions he prefers the AV.

Semen is preserved in different ways depending on when it will be used. All methods require the addition of extender to preserve the semen. Semen to be used immediately may be extended 1:1 (semen: extender). If the semen is to be chilled and transported, the extender is increased to 1:4 to 1:10, depending on final dilution. The accepted dose for insemination of fresh or chilled semen is 500 million progressively motile spermatozoa.
If semen needs to be used more than 48 - 72 hours after collection, freezing the semen is the best option. The main advantage of using frozen semen over chilled is the constant availability of the genetic material contained in the semen. The main disadvantage is that the fertility results can be half those obtained using fresh or chilled semen. Freezing semen has detrimental effects on the spermatozoa, resulting in a 30 - 40% pregnancy rate per cycle. Generally, the accepted dose per insemination for frozen semen Is 600 million spermatozoa, with 300 million progressively motile and morphologically normal.

Mare Preparation

It is of paramount importance that any mare intended for breeding be in optimal health before the beginning of the breeding season. Ideally, the mares should be up to date with vaccinations, worming, teeth and feet. Her overall body condition should be evaluated to ensure she is neither too light nor too overweight because both these conditions will contribute to poor conception rates. A potential broodmares age and status also needs to be considered, as this too will affect the conception and pregnancy rate. Studies have shown the optimal period of fertility for a mare is between 6 and 11, and, correspondingly, foal birth weights appear to be optimal when a mare is between 7 and 11 years of age. This is not to say that an older mare cannot successfully conceive, carry her pregnancy to term and have a healthy foal, it just requires careful management.

Studies have shown a mare reaches her sexual maturity at 4 years of age. When a young maiden mare (less than 4 years old) is being considered for breeding, it is wise to choose one that is physically mature and not too timid. The mare needs to be able to handle the demands of pregnancy and lactation without compromising her own, or her potential foals, well being.

Mares in athletic training or that have been recently retired perform at their best reproductively when they are allowed time to settle into the reproductive rhythms of her body. Many athletic mares need time to unwind from their peak training, undergo withdrawal from anabolic steroids they may have received, and get reaccustomed to a change in diet and being out with other mares and competing in a herd situation before they will become pregnant.

Manipulation of the Breeding Season and Oestrus Cycle

Horses are seasonally polyoestrous (long day breeders). Increasing day length in early spring stimulates cyclical activity, which involves waves of development and regression of ovarian follicles, until an ovulation occurs. These ovulatory cycles are approximately 21 days in length and last through spring and summer. In autumn most mares cease ovulating and cycling, only a small percentage will continue to cycle through winter.
For historical, rather than physiological reasons, the southern hemisphere?breeding season begins with the horse's birthday on the 1st of August. With the equine gestational length being approximately 11 months, mares have traditionally been served from mid?September onwards.

Hastening the onset of the ovulatory oestrus activity mostly requires hastening the onset of the transitional period, as in practice this period cannot truly be significantly shortened. Equine reproductive physiology can be manipulated in a number of ways, including hormonally, to suit manmade demands.

Artificial lighting to extend the day length, or photoperiod, tricks the mares system into believing spring has arrived earlier. Mares exposed daily to an artificial photoperiod of 16 hours will experience their first ovulation 60 to 90 days after the light program starts. The lights can be fluorescent or incandescent, a 100 ?150 watt bulb or 40 W fluorescent tube in a 4 x 4 meter box is sufficient. Alternatively, large floodlights over small paddocks can be used for outdoor lighting systems. It is a good idea to maintain mares under lights until their natural photoperiod has caught up. In colder climates, mares protected from temperature extremes may be more responsive to a lights program, therefore rugging mares during this time can be worthwhile.

Mares in poor body condition begin cycling later than those in good condition or on a rising plane of nutrition. Moving mares to better pasture and/or supplementary feeding in late winter to early spring will produce a steady sustained nutritional increase during the transitional period. Mares that are fat or in good condition at the start of the transition period can be difficult to manage during the breeding season. They need to be fed sufficiently to maintain their body weight without becoming overfat. Overfat mares are often slow to progress through the transition period or they do not cycle regularly throughout the breeding season.

A great deal of research has gone into trying to identify ways to manipulate mares hormonally in order to speed them toward earlier ovulations. Progestagens (Regumate®) mimic the action of endogenous progesterone to induce a hormonal state resembling pregnancy. To induce ovulatory oestrus early in the breeding season administration of Regumate daily for 10 consecutive days regulates erratic follicular activity. When Regumate® therapy is withdrawn, there is a rapid return to normal cyclical ovulatory oestrus, and at this stage, an administration of prostaglandin (Lutalyse® 1ml) is given and will initiate follicle growth.

GnRH Agonists and hCG (Ovuplant® and Chorulon®, respectively) given to a mare when a follicle is > 35mm will effectively induce ovulation within 24 to 48 hours. HCG and GnRH agonists are useful tools and economical methods for inducing ovulation especially when chilled or frozen semen is being used.

Short cycling mares with prostaglandins (PG) is most often done to bring a mare into heat as quickly as possible so that she remains open for a minimum number of days. Administration of PG to a mare with a CL (corpus luteum) older than 6 to 7 days will usually cause luteolysis, return to oestrus and subsequent ovulation within 4 - 7 days.

Failure to respond to PG is a relatively common occurrence in mares and can usually be explained by one of the following:

  • The CL is too young (<6days).
  • The mare had a dioestrus ovulation (2 CL's).
  • A large CL may form after ovulation.
  • If a large follicle is present at PG it may ovulate soon after without the mare showing any behavioural signs of oestrus.

The use of hormonal therapies must be used in conjunction with good management strategies and regular ultrasound scanning.

Artificial Insemination

The majority of breed societies now allow artificial insemination (AI), which has many advantages for the stallion. With AI, a stallion can be collected once every other day, and on the average 10 to 15, mares can be bred with each collection. The other important advantage of AI is that the stallion can be mounted on a phantom mare, thus preventing the chance of injury to the stallion during the mating process. Additionally, the semen can be added to extender containing antibiotics and, thus, minimizing any chance of infecting the mare with bacteria that might be contained in the semen.

Artificial Insemination with frozen semen requires accurate preparation and evaluation of the mares cycle as insemination needs to be performed 4 - 6 hours before ovulation. Using chilled semen is slightly less, 24 - 48 hours, and fresh is 2 days prior to ovulation. Mares prepared for insemination as for natural service, with slight differences because cooled or frozen semen is usually transported to the site of insemination. Both fresh and chilled semen are usually inseminated after using ovulation-inducing drugs. This increases the likelihood of ovulation and in turn increases the chances of pregnancy.

Embryo Transfer

Embryo Transfer (ET) was first performed on horses by Oguri and Tsutsumi in 1972. The procedure involves the removal of an embryo from a donor mare, and transfer to the uterus of a recipient mare, which is approximately the same time from ovulation as the donor mare. Most recovery and transfer procedures are carried out non-surgically at around 7 - 8 days post ovulation.

Donors are selected for the following reasons:

  • To maintain a line of valuable genetic material
  • To allow a mare to continue competing while producing a foal carried by the recipient
  • To assist fertility in older mares who have difficultly carrying and maintaining a pregnancy.

The recipients are chosen based on:

  • Age, 4 - 10 years old
  • Displays regular cyclical activity
  • Has given birth to one or more foals
  • Is similar in size to the donor mare
  • Is healthy and easy to handle.

Low Pregnancy rates after transfer may be due to:

  • Low embryo quality
  • Older embryos damaged by manipulation
  • Consumables not sterile or clean
  • Transfer technique
  • Nutrition and health maintenance of recipients
  • Seasonality (pregnancy rates are higher when mares are cycling actively.) High summer temperatures may negatively affect pregnancy rates

On average, the success rate of embryo retrieval and the success rate of a viable pregnancy in a recipient mare are around 60% and 60%, respectively. In general, a mare owner should anticipate as many as 3 cycle attempts before an embryo is transferred successfully and a foal results.

Pregnancy Diagnosis

In general, pregnant mares will fail to return to behavioral oestrus as expected 17 to 19 days following ovulation and will reject the advances of a teaser. However, failure to return to oestrus does not ensure that a mare has a viable pregnancy therefore manual rectal examination, ultrasound rectal examination or an assay needs to be performed to confirm a pregnancy.

Horses experience a relatively high embryonic loss compared with other species, regardless of how they are bred (AI or natural).

Manual rectal examination of the reproductive tract can be highly accurate for detecting pregnancy as early as 21 days after conception. Changes in the mare's uterine tone and increased cervical tone indicate pregnancy. The embryo itself does not become palpable until approximately 30 days gestation, and the age of the foetus can be roughly estimated in days up until about 90 days. As pregnancy advances, the foetus cannot hide and will be readily palpable to the technician.

Ultrasonography allows visualization of the embryonic vesicle as early as 9 - 10 days after conception. This technology allows pregnancy to be monitored right up to the time of parturition. The first scan is usually performed at day 14 as this is the most reliable time of detection and at day 28, a heartbeat can be detected. Ultrasonography is not commonly used for pregnancy diagnosis after 120 days because of the ease of manual rectal examination however, transabdominal (external) ultrasound can be used to assess foetal development after this time.

Ultrasound technology now enables technicians to sex a foetus at 60 to 90 days. Foetal gender determination is becoming common practice with expensive horses because it allows professional breeders to predict their budget, plan sales and decide early which stallion to book for the following breeding year.

Measurement of progesterone, equine chorionic gonadotropin (eCG) and oestrone sulfate in the blood of pregnant mares at specific periods during gestation also can be useful in equine pregnancy diagnosis. Blood hormone testing can be particularly useful in situations when rectal examination cannot be performed safely. The main disadvantage of this diagnosis method is that the levels do not become significant until later in gestation.

Contact Us

Tristan Starr: 0400 816 072
Mathew Holz: 0417 409 029

105 Chambers Road, Modella Victoria 3816

About Us

Tristan and Mat run the Stallion & AI Center during the breeding season and break-in, train and compete their own and clients horses all year round. Read more...