EHV-1 Vaccine

Love me or love me not, but successful breeding takes more than chance

– An older but updated article covering some of the more important items to consider for success!

By Jos Mottershead
Printed in Atlantic Horse and Pony, Jan/Feb, 1992

This article was written in 1992 and was published in a Nova Scotian magazine. Some of the observations made were in keeping with the time and the location. New methods have since become commonplace, and we have amended the article to reflect this by adding commentary in orange. It is interesting to see the advances in knowledge, technique and equipment availability in the last 20 or so years – but successful breeding takes more than chance!

Breeding horses should be a simple matter, and if it were left up to herds of them on the open range, or on an island of sand in the middle of the Atlantic, perhaps it would be. But often we are working with small numbers of horses, kept in relative isolation and confinement.

For instance, the mare is apparently one of the most infertile domestic animals. It is estimated that the average conception rate of all mares bred in the USA is only 55-60%. The rate in Canada is similar. In fairness to the mare, some of the reasons for these low rates are man made, and so can be eliminated or modified. Too, we now have the techniques to deal with many of the inherent problems. Man-made problems – except for bad maintenance conditions and the misuse of drugs – tend to stem from the concept that most registries hold: that a horse’s birthday is universally January 1 of any year. This is a problem because it encourages early breeding to obtain an early foal with maximum growth potential in any given year. Nature dictates that it is not desirable for a foal to be born in the middle of winter. Therefore the mare is a seasonal breeder; the time of potential delivery being determined by her coming into regular heat only from about April through to September. We are sometimes able to manipulate this natural heat period through the use of extended artificial lighting periods and natural or artificial hormones. Although most mares will respond, not all do.

Mare Condition is Important

One of the most important factors with regards to having a mare conceive is ensuring that she is in good physical condition. This relates to her weight and health. An overly thin or fat mare has less chance of conceiving than does the mare that is just starting to “bloom” or gain a little weight. The mare should be up-to-date on de-worming and inoculations and last, but far from least, the mare should have had a uterine swab taken and cultured and had the results returned negative. If “positive”, then any required treatment should be carried out.

A uterine culture determines whether there are any bacteria present in the mare’s uterus that may be creating an unhealthy environment for the foal to grow in. This is one of the most underrated and yet simplest veterinary breeding procedures. A uterine swab does more than ensure a contaminant-free environment for the foal. It provides a guarantee that the mare is not going to contaminate the stallion with an organism that may be passed on from mare to mare in the case of natural breeding. Another requirement should be that a stallion be swabbed and cultured at the beginning of each breeding season, as this provides the same insurance for the mare owner.

It is now accepted that a uterine swab culture alone is an inefficient method of ensuring a bacteria free uterine environment. The swab sample should first have a cytology smear prepared and read, to look for the presence of neutrophils. If these are present, it indicates an ongoing inflammatory response in the uterus, and the swab sample should be cultured. If neutrophils are not present it is a reasonable assumption that uterine bacteria are not either. Following this protocol will reduce the possibility of a false negative or positive reading of a culture. For more information, see our article on The Importance of a Cytology Smear.

Once it has been established that both stallion and mare are free of infections, the next thing to check is the mare’s ability to provide the stallion with an oocyte to fertilize. (It is being assumed that the stallion is a proven producer and therefore his ability to fertilize is not in question).

Follicle Check – Successful breeding more than chance!

The simplest way to find out whether a mare has a viable follicle, and therefore oocyte, is by means of a rectal palpation. This will establish that the mare, if bred at the right moment, has the potential to conceive. Unfortunately, palpation is a candidate for neglect on “shoestring budget breeding”, even though the cost of 2 or 3 palpations and a uterine swab doesn’t come anywhere near the cost of keeping a non-pregnant broodmare for a year!

It must be remembered that palpation, by itself, is not 100 percent accurate. A mare may have a “mid cycle” follicle present and yet not be ready to breed or ovulate. Indeed, such a follicle may regress and all but disappear before the mare comes into standing heat.

A problem with a single palpation, is that unless one is “follows the follicle”, there is the possibility of an error being made, and what is believed to be a follicle upon palpation, subsequently proves to be a Corpus Luteum (“CL”), or vice-versa. This situation can be overcome, by means of a progesterone assay of the mare’s blood sample. If progesterone is present, it indicates that there is a functional C.L., and is therefore most probably in the diestrus portion of her estrous cycle. This is especially important if a luteinizing hormone is to be used, such as Prostaglandin. Alternatively of course, as is common today, ultrasound can easily differentiate between follicle and CL, as well as determine a mare to be in estrus based upon visible uterine edema.

“Heat” Cycles

Many people who own mares claim that they are able to tell at what point a particular mare is in her heat cycle. However, the only way to gain any good idea is through the use of a “teaser” stallion, by rectal palpation, or by ultrasound. Remember: “Successful breeding more than chance”!

The most common method with live cover breedings is “conscientious teasing”. This process should be carried out by someone who really knows what to look for – the stallion! – or a “teaser gelding” (preferably one that has had testosterone administered to encourage those “stallion habits”). Teasing is not always a quick experience. It can take up to 15 minutes to encourage a shy mare to show to a stallion, and even then 20% of all mares may not show any signs of estrus at all (“silent heat“) and 30% of mares may show signs of estrus during pregnancy! An experienced palpator can take the follicle check a step further by noting whether the mare has recently ovulated. This too helps determine what stage of her heat cycle the mare has reached.


Ultrasound equipment can also be used to establish the breeding condition of the mare’s uterus and ovaries prior to breeding. This is a valuable tool which should be well received when it arrives in your area. Ultrasound is now of course widely available and used. It is considered essential equipment for all reproductive veterinarians.

The Process

From this, we can surmise that the best method of establishing when to breed is a combination (in most cases) of teasing with a stallion and rectal palpation and ultrasound by a veterinarian. Now that we have a healthy stallion, and a healthy time-to-be-bred mare, we can move onto the actual process of breeding.

Cleanliness a Must

Successful breeding more than chance - Preparatory cleansing of the mare

Whether A.I. or natural methods are used to inseminate the mare, cleanliness and maximum aseptic technique are essential. The first “must” is to wash both the mare and the stallion’s genital areas. (An exception to this rule is the stallion that is being used regularly. In this case it has been established that the continued use of soap or other cleansing agents – even water – may prove detrimental because it removes the natural anti-bacterial flora. With such a well used stallion).

Many farms do not bother to wash the animals at all, or only the mare. But if the owner of the mare has gone to the trouble of ensuring a bacteria free environment for the foal by having the mare cultured, why introduce excess bacteria at the time of breeding?

Artificial Insemination or Live Cover?

Successful breeding more than chance - Live Cover

Teasing prior to covering. Note suitable PPE on the handlers and twitch and kicking boots on the mare

One way in which conception rates can be improved is by the knowledgeable use of artificial insemination. By this means, the semen is introduced directly into the mare’s uterus, using a liquid nutrient extender which increases the functional life of the sperm. An added advantage of A.I. is a reduction of the chance of introducing contaminants that may prove harmful to establishing pregnancy. But if A.I. is used improperly, or with insufficient knowledge or equipment, the conception rate can drop drastically. Successful breeding more than chance!

Natural breeding enjoys the reputation of taking less time than A.I. There are a number of reasons for this. For one thing, all A.I. equipment must be aseptically clean or sterile, and any surface that will come into contact with sperm must be pre-heated to body temperature (approximately 38C) to prevent shocking the sperm and causing a malfunction of their abilities. This is where the knowledge and equipment comes in. The Artificial Vagina must be cleaned or have a sterile liner inserted, and must be filled with water heated to the particular stallion’s liking. The tightness must similarly be altered by adjusting the amount of water. Some A.V.’s can also have the tightness altered by adding air.

The stallion must be led to the “jump mare”, or if so trained to the “phantom mare” (breeding mount) and encouraged to mount. Instead of being allowed to breed the jump mare, the stallion’s penis is deflected, usually to the left, and inserted into the A.V. so that when he ejaculates, his semen is captured in the collection bottle attached to the A.V.

AI – Processing Semen

This semen is taken to the laboratory – which any A.I. breeding facility should have set up. There, if an in-line filter was not used (which is preferable), it is filtered to remove the gel fraction of the ejaculate and any detritus such as smegma. It is then checked under the microscope to establish the sperm’s motility and concentration level. Finally, to extend the semen’s active life a nutrient liquid called “extender”, typically containing an antibiotic, is added. The actual quantity of extender that should be used will vary depending on what the semen is to be used for, i.e. shipped semen or on-farm A.I., and the desired sperm concentration. Our semen extender calculator can assist with your mathematics in this matter.

It should be noted that at the onset of the processing, extenders must have been kept as much as possible at 38 degrees Celsius in an incubator or water bath. Provided that the lab is kept at around room temperature (~70°F; 21°C) or warmer, once extended, both the extender and semen may be kept out of the incubator during final processing. Many potential dangers lurk in the lab, including water, sunlight, rubber, lubricants, some antibiotics and spermicidal plastics. Even parts of regular syringes are known to be spermicidal.

Inseminating the Mare

During the artificial insemination process, extreme cleanliness plays no lesser part than before. The extended semen must be introduced through the mares cervix into the uterus, and therefore a little closer to the oocyte to be fertilized. This is achieved by the inseminator putting his sterile gloved and lubricated arm into the mares vagina. After establishing the position of the mare’s cervix, the insemination pipette is introduced through the cervix into the uterus. The syringe containing the semen is already fixed to the other end of the pipette, so when the plunger is pressed down, the sperm are sent on their way.

Artificial insemination is an essentially simple practice once a farm is set up to carry it out. If it is done properly, the farm’s conception rate should more closely approach the 100% mark.

After Breeding – The Old and the New

Once the mare has been bred by whatever method, the next thing to establish is whether the mare is indeed in foal. With the availability of ultrasound, this is no longer the next step! Confirmation by ultrasound of ovulation, coupled with making sure there is no uncleared inflammatory response should be achieved typically on the day after breeding. If uterine fluid is detected, use of an oxytocin protocol may be indicated and beneficial. The first check is done by teasing the mare from about the eighth day post-last breeding through to about the 18th day. If by the 26th day post-last breeding, she shows no sign of estrus while being teased, the mare has a 90 percent chance of being in foal. Pregnancy can be confirmed by rectal palpation from about the 21st day post-last breeding onwards. It is indicated at 21 days by a change in uterine tone, and possibly by a slight bulge in one of the horns at the site of implantation.

Successful breeding more than chance - ultrasound of pregnancy and cyst

Twins or Pregnancy and a Cyst? Actually the latter even though it looks like twins!

Another form of pregnancy detection, unfortunately not commonly available in this area, is ultrasonic imaging, better known as ultrasound. This can be carried out as early as 9 days post-last breeding, but is more usually carried out at around day 15. The use of ultrasound is valuable as it can detect pregnancy prior to the date when a mare would be required to be bred again. If a mare shows a heat cycle at about 14 days post breeding, there is still the possibility that she may nevertheless be in foal. If she is again bred on this heat cycle, which would be the logical thing to do, there is a fair chance that she will reabsorb the foal she already carries. With the use of ultrasound, the mare would be checked for pregnancy prior to rebreeding. Another major use of ultrasound is in the early detection of twin foals. In the event twins are found, they can be monitored to establish whether the mare is in the process of reabsorbing one. If she is not, then one conceptus can be clearly located by the veterinarian using the ultrasound, and pinched off. The remaining conceptus can then be monitored for survival. With ultrasound now widely available, first pregnancy checks are routinely carried out between days 12 and 16 – the day of conceptus fixation – to confirm not only pregnancy, but also the absence of twin embryos. A second ultrasound check should be carried out for the same purpose and to check for an embryonic heartbeat no later than day 28.

A follow-up rectal and ultrasound pregnancy check is advisable between 100 and 120 days post-breeding. If the mare was bred early enough in the year, and no pregnancy is detected at this point, she may be able to be bred again once the endometrial cups have resolved (presuming they were present). In this way an entire breeding season is not wasted.

A Few Last Things…

EHV Vaccine Pneumabort-K

EHV Vaccines can prevent an abortion storm!

Some other items that should be borne in mind for the mother-to-be are the importance of regular de-wormings, although not during the first 90 or last 30 days of pregnancy, and never with an organophosphate de-wormer. (Newer clinical evidence has also suggested a link between feed-though fly control which may contain organophosphates and certain mid- to late-term abortions, neonatal immaturities and associated problems. Caution should therefore be taken if this method of fly control is used. Suitable immunization are also advisable. One immunization that should be of particular importance for pregnant mares is against EHV-1 sub. 1, also known as “Rhinopneumonitis”. This vaccination is commonly given at 5, 7 and 9 months of pregnancy. Other vaccinations suitable for one’s own location should be given to the mare 30-45 days prior to the anticipated foaling to elevate the mare’s maternal antibody levels which will be transferred in colostrum to the newborn foal. Remember – Successful breeding takes more than chance!

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