MANY of our clients with barren and maiden mares are anxious to get their mares covered as early as possible after February 14th but become very frustrated when the mares have not cycled properly until well into March and in some cases early April.

Their frustration leads to phone calls to me to provide a quick fix to get the mare to produce a follicle to enable her to be covered. My first question is have the mares been exposed to light therapy since middle of the previous November?

In many cases the answer is no or only in a haphazard manner. In these situations, hormone therapy will not work as well or as quickly. Mares are seasonal breeders and this is due to the effect of increasing and decreasing daylight hours on an area of the brain that regulates the reproductive system.

In nature, the horses’ breeding season occurs during the light-filled summer months but the universal birthday for many horse breeds is January 1st (northern hemisphere) or August 1st (southern hemisphere). This means we are breeding horses outside their ideal breeding season. Therefore it is much better if barren maiden mares are exposed to a light programme from the middle of November. This has more influence on early cycling in mares than rugging up or giving extra feed.

Providing longer day length for 90 days beginning on November 15th acts to reduce the production of the hormone melatonin and fools the mare’s reproductive system into activating earlier in the year. To date breeders have been achieving this by stabling horses indoors under extended lighting from dusk to 12pm. It is important that the light is of good intensity with reflective walls in the stables to maximise effect. In simplistic terms, the light should be good enough to be able to read a newspaper under them.

Done properly this is a very effective stimulus to the brain for initiating earlier reproductive activity in the mare. However in some instances the lighting is not bright enough and not regulated correctly.

What happens if the light is turned off in the middle of the treatment period? All indications suggest that as few as three consecutive days of interrupted lighting programme can “reset” that programme to the “start” position at best, or even cause the mare to lapse back into winter aneostrus. It is therefore recommended not only to ensure maintenance of the lighting programme once started, but also to maintain the mare on the programme until about 40 days after ovulation upon which she is bred and which results in her being checked in foal or May 1st – whichever happens first.

By maintaining the lighting programme in this manner, in the event that the mare does not become pregnant on the first cycle bred, or loses the pregnancy, she is more likely to return to eostrus.

EQUILUME MASKS

The use of the Equilume masks made by an Irish Company has been a significant advance. It has been scientifically proven that low level blue light will work as well as bright light in regulating the mare’s seasonal activity. Using the Equilume mask ensures proper length and quality light exposure as well as allowing mares to be kept out rather than being stabled.

Traditionally it is best to rough off barren mares from October and to have them leaner rather than fat. Those that are overweight in early January are slower to cycle. Whereas mares that are lean and on an increasing plane of nutrition and weight gain from January cycle quicker and more effectively. The masks enable barren mares to be kept out for longer. This has a number of benefits. The first is that it keeps the mare active which is good for uterine clearance and health. The second is that it is easier to rough mares off this way so that when brought in in January it mimics early spring both in warmth and increasing plane of nutrition. Lastly it may be more economical to leave the mares out than being kept stabled.

The other problem that owners encounter with mares foaling during an artificially imposed early breeding season is longer pregnancy lengths (mares going overdue their time), lower foal birth weight and post foaling reproductive problems (lactational anoestrus). It is only more recently that we have realised that light is the primary influencer of gestational length.

Light therapy for 90 days before due date has been scientifically shown to increase average foal birth weight and prevent prolonged gestation. Traditionally in-foal mares are left out until after Christmas and are not exposed to artificial light therapy. The use of light masks has shown to be effective in helping to normalise gestational lengths and preventing undersized foals.

In conclusion we encourage our clients to review their light therapy systems, making sure the light is effectively bright enough and operated to give proper time exposures. Where it suits to have mares out, light masks are very effective. Obviously other management issues need to be addressed such as diet, shelter and warmth, but these are of lesser importance in regard to early reproductive cycling.

Hugh Dillon MVB, Cert ESM, MRCVS is a member of the Equine Group of Veterinary Ireland and a partner at Troytown Equine Hospital, Co Kildare

Email: hq@vetireland.ie

Telephone: 01 4577976