Mimicking daylight to synchronise the young Thoroughbred racehorses’ internal clock

Aileen Carter is an Enterprise Partnership Scheme Postgraduate scholar based at University College, Dublin and working in collaboration with Equilume. She is is exploring how optimised photo-stimulation that mimics sunlight can improve the growth and exercise capacity of maturing thoroughbred horses.

The Thoroughbred horse is a performance animal capable of elite athleticism. Centuries of genetic refinement for competition purposes have capitalised on their superior physiological traits. Ireland is globally renowned for its ability to breed high calibre Thoroughbred racehorses, and we can be very proud of that achievement. However, modern management of the young Thoroughbred requires that these horses spend a large proportion of their day indoors and are not exposed to optimal daily light intensities or to a natural light/dark cycle. My research is aiming to find a solution to this problem.  

The lengthening days of spring have long been associated with increased fertility, growth and performance. Therefore, horses need light for more than just vision: it synchronises their ‘internal clock’ – a complex control system that coordinates all bodily functions to a 24-hour (circadian) or 365-day (circannual) rhythm. So, without this lighting, a horse’s internal clock can become supressed or out of harmony. As you can imagine, this can lead to impaired growth and performance. We already know how important optimal and regularly timed lighting are for both physical and mental health. These benefits are clearly recognised and implemented for humans, and for growth and production in sheep, chickens and cows. By understanding the qualities of natural daylight, we can mimic these positive effects on physiology using a custom designed lighting system for horses.

For indoor lighting to effectively imitate outdoor environmental light, it must have three important characteristics:

1) An increased amount of blue in the light: as you might know, natural daylight has a considerable amount of blue, short wavelength light. This blue light targets a photoreceptor in the horse’s eye that stimulates the circadian control centre in the brain. If indoor lighting is blue-enriched, this will heighten the horse’s activity and alertness levels and enhance their feeling of wellbeing.

2) Simulating the seasons: indoor lighting must change in step with natural dawn and dusk, taking place at regular times and gradually changing over the course of the year to mimic the seasons. This will direct the horse’s expectation of daily exercise and feeding regimes and regulate and support its 24-h rhythm.

3) Uninterrupted at night: Dim red light or darkness at night is necessary for horses to experience a nightly elevation in a hormone called melatonin, which regulates internal timing. The white light that is commonly used at night disrupts melatonin production and reduces rest, immune function and daytime performance capacity.

My study aims to encourage trainers to use optimal and regularly timed lighting in training regimes in order to improve welfare, growth, health and performance. The ways in which the spectral composition of the lighting will be clearly defined and time managed makes my work different from previous studies. Another original feature of my work is my use of state-of-the-art next generation sequencing to investigate changes in how genes are expressed in the horse’s skeletal muscle in response to training under different lighting regimes. I’ve chosen next generation sequencing because it is a very appropriate platform to allow further species comparative studies to be carried out. Hence, future researchers, regardless of what species they are studying, will be able to make meaningful comparisons to what I will find in my study.