Blue lights dotted across the landscape of the Thoroughbred breeding hubs of the northern and southern hemispheres have become a common sight as a new equine breeding technology is embraced by horse breeders. The source of the light? An innovative mobile lighting device for horses; the Equilume Light Mask (ELM). The technology was developed by University College Dublin researcher Dr. Barbara Murphy, who identified the optimum light level required to advance the breeding season.
In 2011, Dr. Murphy and colleagues at University College Dublin investigated the threshold level of blue light required to inhibit circulating concentrations of melatonin in the horse. The efficient interpretation of blue light by the translating structures (melanopsins) in the eye had previously been demonstrated in other species. It was noted that very low intensities (lux) are required and that it is neccessary to deliver this low frequency light only to a single eye in order to inhibit circulating melatonin to daylight levels in the horse.1,2 A follow-up study was conducted in Kentucky, USA. By decreasing the duration of circulating melatonin, the secretion of GnRH is facilitated, allowing for the increase in the pulse frequency of FSH and LH and,in turn, reproductive activity.
The ELM, worn by non-pregnant mares maintained outdoors on pasture, was shown to advance the first ovulation of the season as effectively as standard barn lighting.2 But what about pregnant mares? Without the light signal to translate the seasonal changes in day length into a hormonal signal that signifies the correct time of year for foaling, it is thought that this leads to longer gestation periods in many mares and often lower foal birth weights.
The use of this mobile lighting technology to alleviate the issues faced with pregnant mares in an imposed breeding season was investigated in Ireland and in the USA. In 2011 a group of pregnant mares with a history of prolonged gestation lengths were provided with an artificially extended day length from 1 December. The analysis of the results demonstrated a significant difference in gestation length between mares which received an artificially extended day length and mares which were exposed to the ambient photoperiod (p<0.05). When comparisons were made between the mares who received the light treatment and their previous gestation periods, a significant effect was again noted (p<0.05). 3
From this work it was concluded that low intensity blue light delivered to a single eye from the automated device reduced the gestation length in mares who had previously demonstrated prolonged gestation periods.3
The effect on gestation length has been experienced by commercial users of the ELM. An in depth analysis on one such UK based stud demonstrated a significant difference when comparing average gestation lengths over a 5 year period. The mean gestational period of mares in the 2014 season, when the ELM was used, was 9.5 days shorter than the average gestational period of the previous 5 years (p<0.05). When compared with just the previous seasons (2013) average gestation length, a difference of 15.3 days was noted (p<0.001).
A study conducted in collaboration with the University of Kentucky in 2012 investigated the effect on foal birthweight. A group of mares, all inseminated using the same sire, were divided into two groups: half were fitted with ELM’s to provide an artificially extended day length and half were maintained under ambient light conditions. The birthweights of the foals produced were compared between groups. A significant difference was noted (p<0.05), with the foals born from mares receiving artificially extended day length from 1 December until foaling in March an average of 8.4lbs heavier than their counterparts from mares exposed to the ambient photoperiod.
The seasonal production of prolactin as regulated by the lengthening hours of daylight is in part responsible for the shedding of a winter coat. The use of artificially extended day length to hasten the shedding of a winter coat is widely practiced in many disciplines. In 2014, a study was conducted in Japan to investigate whether low intensity blue light delivered to one eye on a group of Thoroughbred yearlings could successfully advance the annual moulting pattern in an outdoor maintenance regime. The coat condition was significantly improved (p<0.05).4
The benefits of extended day length on aspects of the horse is well established. As seasonal breeders, horses are designed to be at peak physical functionality during the long summer days. The advantages of simulating this in a timeframe that suits our schedules are many; the advancement of the first ovulation of the season, improvements in coat conditions for competition animals and also evidence of improvements in colostrum quality.
REFERENCES available on www.vet360.vetlink.co.za