Horses are seasonal breeders – this is why most foals in the Southern Hemisphere are born during spring and early summer. Their reproductive systems depend on natural sunlight to function. Mares have multiple oestrous cycles throughout the warmer seasons of the year. When the seasons turn colder, a mare’s reproductive cycle becomes irregular and therefore she will be less likely to come into heat during winter. Stallions also experience a decrease in sperm production during the cooler months of the year, as a response to the shorter length of daylight.
This month, HQ takes a closer look at using artificial light for breeding. We spoke to respected veterinarian, Dr Duncan Prinsloo (Jnr), from Embriosem, about the effects of artificial light breeding.
How it works
Mares typically need 16 hours of light and eight hours of darkness to maintain reproductive functions. During the colder winter months, we get between 10 and 12 hours of light in a day, depending on the area of South Africa.
Artificial lighting is primarily used to manipulate a mare’s biological cycle by resuming her oestrous cycle earlier than what is considered normal. When a horse is exposed to light, that light enters through the horse’s retina and suppresses the release of the hormone melatonin from the hypothalamus (the part of the brain that controls the endocrine system), and the anterior pituitary (a major organ belonging to the endocrine system). Gonadotropin-releasing hormone (GnRH) is released from the hypothalamus and stimulates the production of a luteinising hormone and a follicle-stimulating hormone. These hormones act on the ovaries, thereby promoting follicular development and the consequent ovulation of eggs.
Who uses artificial lighting?
Artificial lighting is widely used in the Northern Hemisphere, where days are very short during the colder months of the year. The Europeans try to bring their horses back into their reproductive cycles earlier, so that they foal earlier as well.
Dr Prinsloo tells HQ that Thoroughbred breeders, in particular, make use of artificial light for breeding purposes. He elaborates that the birth of a Thoroughbred foal has huge consequences for the racing industry. South African Thoroughbred mares usually foal down between September and early December. Thoroughbred breeders want foals born as early as possible, so the use of artificial lighting in an attempt to conceive and consequently foal down early, makes sense.
In South Africa, hardly any Warmblood breeders make use of artificial lighting, and this is true for sport horse breeders in the Northern Hemisphere as well. Light-influenced breeding is most beneficial to Thoroughbred breeders, because of their specific racing seasons, whereas other disciplines usually run year-round, so there is more leeway when it comes to the birth of other breeds.
Where to install artificial light
Most breeders will install a neon light in a mare’s stable. Dr Prinsloo explains that researchers have developed a formula that specifies exactly which bulbs to use in order to optimise performance. According to Bradford Daigneault, author of the article Artificial Lighting: Preparing for Early Breeding, the rule of thumb is that the light should be bright enough to be able to read a newspaper in the stable.
Timers are usually put in place to turn on at dusk, so that the dusk period is perceived by the horse to be longer. These neon lights usually stay on for four to six hours to extend the day to the length of a typical summer day. In last month’s issue of HQ, we looked at the Equilume light mask, in particular. These masks feature low-level blue lights on either side. They are self-activating and automatically timed.
When to start
Dr Prinsloo told HQ that what many people don’t know is you have to start using the artificial lighting approximately 60 days before a mare’s biological cycle. This is to promote maximum effectiveness of the artificial lighting. Mares often go through a transitional phase during the end of winter and beginning of spring, which can result in unpredictable and irregular cycles. If breeders start using artificial lighting in advance, then a mare will already be experiencing a normal oestrous cycle before her first breeding attempt.
Some believe that artificial light can also be used on horses to promote summer coats and condition, since it ‘tricks’ the horse by extending day length. Dr Prinsloo thinks that using artificial light to stimulate short and shiny coats is probably not very effective, as coat condition has more to do with temperature than daylight. There is a reasonable chance that it could work; however, there are few success stories.
There was mixed feedback when this science originally went public. Some questioned whether the practice is cruel and whether or not it is ethical to interfere with a horse’s natural breeding cycle. Dr Prinsloo told HQ that, to date, no one has been able to prove any negative side effects of using artificial light. According to research, the horses do not experience any discomfort while being exposed to neon or blue light. Although the light masks feature light sources much closer to the eye, Dr Prinsloo explains that this should not be a problem, as long as the light is not set too brightly.
Popular in South Africa?
Dr Prinsloo says that South African breeders are not using artificial light as widely, because our spring starts early enough, owing to our position relative to the equator. He believes that although South Africans are not using the science as much as the Europeans, people do know about it and breeders can easily approach veterinarians about using artificial lighting.
Source: Artificial Lighting: Preparing for Early Breeding by Bradford W. Daigneault
Text: Charlotte Bastiaanse