The dry mare tends to be treated with in an “off-handed” manner by the broodmare owner, with expectations that she will fall straight in foal at the beginning of the serving season. NOT SO! The very nature of the reproductive cycle of the dry mare combined with the imposed August 1 birthday makes it very difficult to achieve an early pregnancy.


THE DRY MARE CYCLE

Commonly, the dry mare is not reproductively active during the winter – i.e. she does not cycle. This is referred to as her anoestrus period. (See photo 1)

With the onset of spring the mare is stimulated into the cyclic phase by three major factors;

1) DAYLIGHT LENGTH (the lengthening of;) – the most important of the factors
2) NUTRITIONAL UPSWING – critical body mass is required for individual cyclicity
3) TEMPERATURE – increase of;

These factors are recognised by a particular portion of the brain, the hypothalamus. Such recognition will cause the commencement of hormonal interaction, encouraging the mare to start her first reproductive cycle for that year. She will then enter her “Transitional or Spring heat”.

Her first developing follicles may regress and develop for some time before the mare finally achieves her first ovulation of the season. She will display varying degrees of oestrous (show receptive behavior to the stallion) throughout this period. Finally she will achieve ovulation. Conception is not possible until immediately prior to this ovulation. After her first ovulation the mare will become a normal cyclic, sexually active mare.

The length of time a mare stays in transitional oestrus varies from mare to mare and season to season. In the natural situation this period may continue for some weeks, even months.
 
On the following page I have included some ultrasound photos of follicles in the transitional mares, and a good example of what ovulation looks like. The numbers down the left side of the photos indicate centimeter increments.
 
For a mare to be due to foal on August 4th, she needs to be bred September 1st. In Victoria particularly, it is a big ask for a mare to be fully cyclic by this time, in-fact without artificially interfering with the mares cycle, in a cooler climate only about 20% of mares can be expected to be cycling by early September. Understandable really when we take into account that early September is an awfully long way from the longest day of the year, the weather is barely warming up, and Spring grass is only just appearing.
 
Realistically, any person who wants to significantly increase the chance of an August, and even a September foal must consider artificially extending the daylight length.


PLACING MARES UNDER LIGHTS
Placing mares under lights is an extremely successful method of getting mares fully cyclic within certain timeframes. In other words we can set up for an early September serve in most cases. Fortunately, light therapy is very simple to do, and is an option that many private breeders can do themselves with a little setting up and forethought. Most dry mares do not turn up at stud until early September anyway, so why not send them “ready to go”!
 
From the time of commencing light therapy to having nearly all mares cycling properly takes about 60 days if done correctly. That means for an early September serve, mares need to commence going under lights at the beginning of JULY. For those who are not so fussed with an August foal the starting date is not so critical, however the option of lights in cool climates should be seriously considered. There are still many dry mares that are unable to be covered before mid October.

The Method
For the purpose of these notes, I am only going to outline old “tried & true” practices that are simply done in most home environments.

The mare requires:

• 16 hours of light, but more importantly 8 hours of darkness
• Light intensity strong enough that from any area of the mare’s available space, a newspaper can be comfortably read.
• While we’re at it, we may as well increase temperature, and put a rug on the mare.

The ideal situation is access to a powered stable. The lights used can be normal fluorescent or incandescent lights, as long as they do not shadow too much in the corners. The accuracy of darkness/light ratio is critical – and yes, leaving the lights on all night or forgetting to turn them on occasionally is detrimental. Please, do not consider placing mares under lights unless you use a timer switch – it is the only way to guarantee that the process is done properly. The best ones are those that can be set twice in a 24 hour period. This way the lights can be set to go on at say 5:30 p.m., switch off at 8:00pm, on again at 5:00am, and off when it is quite definitely light, or for dark stables, after the mare has been turned outside for the day.

A yard can be used for lights, but the power of the light, and placement of light (possibly lights, plural) need to be carefully looked at to meet the required criteria. It must be also remembered that yards are prone to bogging. Certainly the mare would require rugging.

The mare should be able to access a good, well-grassed paddock during the daytime.
 
If you are uncertain how to apply light therapy in your situation, your veterinarian will be able to help, or you may contact us.





SIMPLIFIED DIAGRAM OF EVENTS TO ACHIEVE FIRST OVULATION :



The mare is stimulated into the cycling phase by three major factors;
1. DAYLIGHT LENGTH (the lengthening of ;) (PHOTOPERIOD) - The most important factor.
2. NUTRITIONAL UPSWING - critical body mass is required for individual cyclicity.
3. CLIMATE, or more accurately, TEMPERATURE.

These factors are recognized by a particular portion of the brain, the hypothalamus. The hypothalamus has a hormonal releasing factor, GnRH (GONADOTROPHIN Releasing Hormone), which travel to the pituitary gland and stimulate the release of FSH and LH. These hormones target the ovary to develop the follicles and cause ovulation respectively. It is the lagging of the LH supply that is responsible for the slow maturing of the follicle to cause ovulation. Eventually in response to increasing photoperiod LH secretions become adequate to progress a follicle to maturation and ovulation.