Your Mares Cycle Early, Foal on Time with Optimum Birth Weights


Horses are seasonal breeders, their natural breeding season occurs during the light- filled summer months.

However, the universal birthday for many horse breeds is Jan 1st (Northern Hemisphere) or Aug 1st (Southern Hemisphere).

These industry wide crucial dates create a demand for early foals, in order to produce mature yearlings and precocious two year old horses.

Changes in the length of daylight is the primary regulator of reproductive activity in the horse. The hormone melatonin is produced during the hours of darkness and acts as the decoder of daylength for seasonal breeding animals such as the horse. The time of year is directly translated through this relationship; as the days lengthen in Spring, melatonin production decreases signalling the approach of the breeding season.

Mares foaling during an artificially imposed early breeding season often experience:

  • Longer gestation lengths
  • Lower foal birth weights
  • Post-foaling reproductive problems

Late foaling mares represent economic loss to the breeder by reducing the number of foals a mare can produce in consecutive years. Mares that foal outside of the natural breeding season (e.g. Thoroughbreds) have longer gestation lengths by an average of 10 days. However, 20% of Thoroughbred mares experience annual gestation lengths that exceed 355 days.

Light is the primary influencer of gestation length. Light therapy for 90 days prior to foaling has been scientifically shown to increase average foal birth weights and prevent prolonged gestation.

Length of Gestation in days - Thoroughbred

Field Trial 2012 - Pregnant mares

  • 15 pregnant mares with a history of long gestation lengths were divided into two groups.
  • One group was fitted with prototype Equilume™ Light Masks on Dec 1st

Mare Gestation Length


The Equilume™ Light Mask reduced the average gestation length of pregnant mares by 11 days (Walsh et al, 2012. MSc AgrSc Thesis, UCD)

Field Trial 2013

  • A group of 30 mixed breed pregnant mares due to foal Feb - March were selected
  • 15 of the mares were fitted with Equilume light masks on Dec 1st


The average birth weight of foals born to the group of mares wearing the Equilume Light Mask was significantly greater by 8.4 lb

Providing longer day-length for 90 days beginning on Nov 15th (NH)/Jun 15th (SH) acts to reduce the production of the hormone melatonin and stimulates the mare's reproductive system to activate earlier in the year. To achieve this, many breeders stable horses indoors under extended barn lighting and incur substantial costs associated with bedding, lighting and labour. The average keep fee for a barren mare in Ireland is €20.05 per day, according to the Irish Thoroughbred Breeders Association Cost Survey 2013. Therefore, standard indoor light therapy for 100 days equates to approximately €2000 per mare per season.

Field Trial 2012 – Maiden/Barren mares

  • 26 non-pregnant mares were fitted with prototype Equilume Light Masks and maintained outdoors at pasture from Dec 1st
  • 16 mares were maintained indoors under standard stable lighting
  • 20 mares were outdoors at pasture without light (control).

Reproductively Active Mares light mask vs stable light


Over 90% of the mares in the group who were maintained at pasture wearing Equilume Light Masks and the group maintained indoors under stable lights were reproductively active on Feb 10th. Equilume is as effective as standard stable lighting at advancing the breeding season in mares. These results were published as a paper in the Equine Veterinary Journal (Murphy et al, 2013).