02-14-2011, 08:16 PM
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Mares normally cycle from early spring to late fall. A 'normal cycle is every 21 days. In mid-season, a mare is normally in heat 2 to 7 days and out for 15 to 18 days. They ovulate toward the end of the cycle.
Most mare that are kept outside do not cycle in the winter unless they are on wheat pasture or live in the sunny south. This period of time is called 'anestrus'. They are not fertile.
When mares start cycling in the spring, they may stay n heat for 2 or 4 weeks on their first cycle, but will only ovulate once near the end of the cycle. Cycles this time are year are very erratic and not very fertile. This is nature's way to keep foals from being born in the winter months.
Horses stalled and on good feed frequently cycle all year 'round. These are usually fertile cycles and are particularly so if they are under lights 16 hours a day.
It is a pretty good bet that most mares are not very fertile until they have shed about half way out and their necks and shoulders are 'slick'.
A 'Caslick's' suture is where the upper half of the vulva is sewn together leaving room below it for the mare to urinate. It is done mostly on race and performance mares to keep running and performing mares from 'sucking wind'. This is when a mare has air fill their vaginal cavity.
It is also done on older mares that have a 'tilted vulva'. Many older mares have a rectum that is recessed back into their body cavity. This tilts the vulva forward and it catches manure when the mare defecates. This allows for fecal and bacteria contamination and keeps the mare infected.
For either reason, it is better to keep performance mares and older mares sutured. This does not affect heat cycles.
Hope this helps.