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Serving Methods and Common Hormonal Treatments by Walter Berger

The first part of the article will go through the advantages of different breeding methods which may be used. It also summarizes some of the advantages and disadvantages of each method.

Paddock serving could be used with a stallion and a small number of mares. Up to 15 mares would represent a number found in a natural herd environment. This would only be used in a small operation as it limits the number of mares a stallion can serve.

An important guide line is the temperament of the horses involved. A good dependable temperament from both the mares and the stallion would be required in order to keep injuries to a minimum. With valuable animals this method would be inappropriate due to the possible risks and lack of control on the serving process. But generally the conception rate would be about 90% as the stallion is able to monitor the mares constantly as to when they are ready for mating.

Introducing new mares to the herd can represent unacceptable risks to the new animal, especially if she is only on the property in order to be served. This is because of the settling in period as the mare establishes her spot in the herd hierarchy. This could limit the members of the herd to a permanent group belonging to the stud.

: This method has the minimum labour content due to the hands off approach. This also means that a minimum of time needs to be spent as the animals don't need to be handled as much. It could be approached as a one person operation. The mares should still be monitored for any problems.

Facilities: Minimum facilities are required as the animals run in the one paddock and aren't brought in for serving, teasing, etc. A crush would still be required if any of the mares needs or is wanted to be examined. The other option would be to float the animal to a Veterinary clinic that has facilities when an examination is needed.

Costs: Due to the small labour input required and the minimal facilities needed the costs of this type of operation would be low.

Number of mares
: In order not to overtax the stallion 15 mares would be about the maximum number of mares. During the peak reproductive period between December to February you could expect at least 80% or 12 mares to be cycling. This means that in a  24 day period you would have about 60 days of oestrous and you could expect the stallion to serve about 3 mares a day. This is assuming the stallion has not been with the mares since the start of the season, in which case you would expect several of the mares to be pregnant already.

Diseases: Due to the constant interaction of animals in the herd there is very little control over disease spread. The herd needs to be monitored constantly in order to minimize any outbreak. If any mares from outside the stud are serviced at any stage, then these should be examined for any disease to stop any cross infection to the herd.

(Rossdale, P.D., 1987), (Rossdale, P.D., 1992), (Kerrigan, R.H., Rodger, J.A., Morgan, J.R.G.,1990)


This method is commonly used on studs as it represents lower risk to the horses involved and gives fairly good success rates. It gives you total control over which mares the stallion serves and how often. But the conception rate tends to be 40% to 50% lower then in paddock serving.

This type of serving should be used when valuable animals are involved. It is also preferable when the temperament of the stallion or mare is bad or unpredictable.

Number of mares
: Individually serving the stallion is able to cover more mares. A stallion up to 4 or 6 years of age (depending on the physical maturity and libido) should be able to cover a mare a day. Older stallions can be expected to cover up to 3 mares a day, but 2 is a more accepted number. With mares needing to covered up to 4 times to conceive, the numbers of mares a stallion can serve a year is limited to between 20 to 60 (depending on the above factors).

Diseases: With the stallion and mares being separated the spread of disease is easily controlled, as long as the mares are examined before being allowed to come in contact with the stallion.

: This method is more labour intensive as the mares have to be individually teased. Accurate records have to be kept as to when they are in oestrous, how often they have been served and results of pregnancy tests and any other relevant data.

At least two people are required during serving. Depending on the mare some restraint may have to be used including fetlock hobbles, kicking boots and twitches. The tail should also be bandaged.

Facilities: Individual paddocks or yards will be needed in order to separate the stallion and the mares. The stallion yard should be a good size of at least an acre and in an area where the stallion can see the goings on at the stud. This allows him to get some exercise and stops him from getting bored by having lots of things to look at. The fence should be of solid construction and about 1.5 meters high or electric. It could also include a section suitable for teasing. This should be of solid construction so that feet can't get caught while striking out. This should adjoin a laneway so that mares can be brought up to him.

More ideally a stallion box should be available and a separate teaser stallion should be used in order to prevent the stallion from getting frustrated. Serving itself can be carried out in a small yard or other area with good footing. A separate, enclosed area would be better as any distractions would be removed. This area could also include an area to restrain a foal and still keep it in sight of the mare.

A crush is also needed to facilitate any examinations of the mare, unless the animal would be floated to a clinic with the necessary facilities. This would be impractical for the larger number of mares usually involved in hand serving.

Costs: The fact that more facilities and labour is needed makes this a more costly proposition than paddock serving. This could be out weighed by the fact that you should be able to serve at least twice as many mares, which should enable any extra outlays to be recouped within a fairly short time frame. Ideally the mares should be pregnancy tested to ensure maximum conception rate. This can get expensive, especially if both 12 and 45 day testing is used and ultrasound is utilised as well.

Blood tests are a cheaper alternative to ultrasound and usually involves testing for Pregnant Mare Serum Gonadotrophin.  This is produced as follows.

  •             Day 14 to 15:   Uterus lining recognises embryo presence, prostaglandin release is inhibited.
  •             Day 15 to 35:   Progesterone from corpus luteum causes uterus lining to thicken and release nutrient fluid.
  •             Day 35 to 37:   Embryo cells invading the endometrial wall form endometrial cups.
  •             Day 40 to 120: endometrial cups release pregnant mare serum gonadotrophin (PMSG).

The disadvantage of this is you have to wait 40 days to test and abortions aren't detected early enough in order to get the mare to cycle soon.

(Rossdale, P.D., 1987), (Rossdale, P.D., 1992),(Kerrigan, R.H., Rodger, J.A., Morgan, J.R.G.,1990)


Artificial Insemination A.I. is best used under one or more of the  following circumstances.

- The stallion and the mare are a great distance apart and moving one to the other is impractical.

- It is not possible to mate the stallion and the mare naturally due to physical causes.

- The stallion refuses to serve the mare or the mare refuses to be served.

- There is disease present in either the stallion or the mare that is transmitted by physical contact.

Number of mares
: With A.I. the number of mares a single stallion can serve is increased up to five times. A standard ejaculate contains about 50 ml of semen and 10 to 15 ml are required to serve one mare effectively.

Diseases: The spread of disease is easily controlled, as long as there is no disease present in the ejaculate.

Facilities: The same facilities as for hand serving would be required. This is because the mare still needs to be teased in order to assure that she is in oestrus before A.I. is used, and semen still needs to be collected from the stallion if using the stallion from the stud. Then an artificial vagina would be required and a clean area in which to examine, handle and store the semen.

Costs: The cost of using external stallions is less by using A.I. but the success rate is also less than using natural serving.

Labour: As skilled labour is required to perform A.I. successfully and safely, it is usually best performed by a veterinarian, but it is possible to become qualified in A.I. by completing an appropriate course.

Pregnancy rates
: The handling of the semen is crucial as it easily killed by light or temperature changes. Semen is best used fresh, but can stored under the appropriate conditions for up to 72 hours. This is achieved using Equitaners, which keep the semen at 5oC. It can also be stored frozen in liquid nitrogen, but this reduces fertility drastically. Fertility rates can be up to 80% using fresh semen and down to 40% with frozen semen.

(Rossdale, P.D., 1987), (Rossdale, P.D., 1992), (Kerrigan, R.H., Rodger, J.A., Morgan, J.R.G.,1990) 



This part of the article will go through a Mares Oestrous cycle and common hormonal treatments which may be used in Broodmares



Receptile contains GnRH. This is often used to cause a mare to cycle early in the season. It is administered in regular doses to mimic the natural burst of hormones usually found. It may be injected or given via an implant that releases doses at required intervals.

This product contains the luteinising hormone hCG (human chorionic gonadotrophin). If there is a follicle of suitable size of 3 to 4 centimeters present, administering this hormone can stimulate ovulation. This can be useful for either for causing ovulation at the second FSH surge at mid dioestrous, shortening a lengthy oestrous period or inducing ovulation at a specific time. Ovulation usually occurs within 24 to 48 hours.

Care needs to be used when using  hCG as some mares may go into shock on receiving it. Other mares may develop an immunity to it after several uses and it becomes less effective.

This contains FSH. This may be used to stimulate the ovaries into follicle production at the start of the season when the natural burst of FSH may be low.

Both of these contain prostaglandin. This may be injected in the case of a retained corpus luteum, which will stop cycling due to the progesterone released. This will simulate the prostaglandin released by the uterus. The regression of the corpus luteum caused by this will allow for the release of FSH (follicle stimulating hormone) and LH (luteinising hormone) to occur and start cycling.

They can also be used to cut short dioestrus. This is useful to synchronise cycling in a number of mares. In case of a second ovulation at the mid dioestrus FSH surge this will not work as the second corpus luteum will repress the action of the prostaglandin.

This product contains progesterone. Progesterone is usually administered for a period of about 10 days and then stopped. The treatment has the effect blocking the release of FSH and LH. When the progesterone level drops after treatment, FSH and LH are released in a burst usually sufficiently large enough to begin cycling. This causes a follicle to mature in 7 to 10 days.

Oxytocin is produced by the posterior pituitary gland normally. This hormone may be used to induce foaling in a pregnant mare. It is usually only used to induce birth with a mare carrying a dead foal, or for other reasons that endanger the mare if the foal is carried full term.

Given too early to a mare the foal may be premature and not be able to live unassisted. Also the structures of the birth canal in an induced mare would not normally have relaxed to the same extent as in a normal birth.

(Rossdale, P.D., Ricketts, S.W. , 1980), (Rossdale, P.D., 1987), (Rossdale, P.D., 1992), (Kerrigan, R.H., Rodger, J.A., Morgan, J.R.G., 1990),  (Dr. G. Blenkhorn).


Rossdale, P.D., Ricketts, S.W. 1980
Equine Stud farm Medicine
Bailliere Tindall

Rossdale, P.D.Date1987
Veterinary Notes for Horse Owners
Stanley Paul & Co. Ltd.

Rossdale, P.D.Date1992
Horse Breeding
David & Charles

Evans, J.W.1989
Horses: A guide to Selection, Care and Enjoyment
W. H. Freeman and Company

Kerrigan, R.H., Rodger, J.A., Morgan, J.R.G.1990
Practical Horse Breeding
Wilderness Publications Pty. Ltd.

National Research Council1978
Nutrient Requirements for Horses
National Academy of  Sciences


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