The Mare's
Oestrus Cycle
By Linda Kennard of NAF
There is a rhythm to nature, the rhythm of the seasons and the rhythm of plants going through their cycle of planting, growing, harvesting and resting. There is also the rhythm of the mare. As with the plants the seasons play an influencing role with the mare in ovulation, conceiving and carrying a foal full term.
The mare's reproductive activity is considered to be seasonally polyestrous. This means that the mare has a non-reproductive season, known as anoestrus and a reproductive season. The non-reproductive season, anoestrus, is during late autumn and winter. The reproductive season falls during spring and summer, with the highest efficiency coinciding with the longest day of the year June 24th. During this period nearly 100% of mares will be cycling. During anoestrus season, which coincides with days when there is little light, only a small amount of mares will cycle and ovulate.
During the reproductive season most mares have a 21-23 day oestrus cycle. This oestrus cycle can be divided into two: Oestrus which lasts 4-6 days, is when the mare is receptive to the stallion, and dioestrus which lasts 15-17 days.
Oestrus
This is when the mare will be receptive to the stallion. She will be showing typical signs of oestrus such as adopting a urinating stance and passing small amounts of urine. This is normally bright yellow in colour. Also she will avert the vulva to expose the clitoris, this is known as winking. The mare could also demonstrate varying mood swings. During oestrus the follicle on the ovary increases in size and ruptures to release an egg, this is ovulation. Ovulation generally occurs late in oestrus about 24-48 hours before the end of oestrus.
Dioestrus
During dioestrus the mare will become aggressive towards a stallion. Her ears will be pinned back, the tail will swish and she may even squeal.
The Ovaries
Mare's ovaries are unique amongst mammals both in size and make-up. The two ovaries in the mare are situated ventrally to the fourth and fifth lumbar vertebrae. The two ovaries contain the female gametes (ova or eggs). There are many thousands of gametes present in the ovaries from birth and no more will be produced during the mare's lifetime. The ovaries are shaped like kidney beans and will vary in size depending on age and whether the mare is in oestrus or dioestrous. During dioestrus (non-breeding season) the mares ovaries can measure 2-4cm in length and 2-3cm in width. They will normally be hard to touch. During oestrus (when the mare is in season) the ovaries will increase in size to 6-8cm in length and 3-4cm in width, they will also become softer to touch due to the development of fluid filled follicles.
The Ridden Mare
It's often said that when you get a good mare, then you've got a good horse, and she'll give you her all. The mare's hormones can work in your favour as they give her staying power and heart. However, those same hormones can also work against you, as all mare owners will know!
It is very important to remember that a mare is an entire horse, just like a stallion. So, she has much more to cope with than a gelding. Her oestrus cycle can be dysfunctional and her hormone levels incorrectly balanced, as applies to all females of any species. The mare's problem is exacerbated because we want to saddle her up and ride her!
With the ovaries increase in size and their location (just behind the saddle) it is understandable that when ridden this area can become uncomfortable for the mare. This discomfort can lead to mood swings and grumpiness which many mares display during oestrus.
The oestrus cycles are under hormonal control and problems can arise. The mare is most fertile April, May, June and July, however during spring and autumn some mares will ovulate with no signs of oestrus while other mares will have prolonged periods of oestrus behaviour and not ovulate. During these periods the mare's behaviour can become erratic, aggressive and she may become difficult to ride.
Nutritional support can be given help to regulate the mares oestrus cycle. Targeted nutrients can help her to naturally balance her own cycle herself.
Recommended NAF products:
Oestress - helps your mare to help herself
For more information please call the NAF
Freephone advice line: 0800 373 106, email info@naf-uk.com or go to www.naf-uk.com
