By Kentucky Equine Research Staff

Many horse owners are familiar with using artificial lights on broodmares to advance the breeding season or on show horses to help keep short, slick hair coats. Recently, Japanese researchers used artificial lighting on young, growing Thoroughbreds and found that extending a yearling’s photoperiod in winter increased muscle mass. The use of artificial lights to manipulate muscling may offer a unique way of helping prepare young horses for their two-year-old careers.

Previous research found that young Thoroughbreds bred in northern Japan, Hokkaido, suffer a decrease in growth rate in the winter between weaning and the first year and again between the first and second year of life. Further, there is a lower rate of increases in body weight, height at withers, girth circumference, and cannon bone circumference in the winter between the yearling and second year compared to young horses reared in southern Japan where the photoperiod is longer.

The increased rate of growth in Thoroughbreds raised in southern Japan is thought to be, at least partly, attributable to the activation of hormones involved in the hypothalamic-pituitary-gonadal axis as well as the growth hormone-insulin-like growth factor-1 axis as the photoperiod lengthens.

Another published study in Japan reported that the growth rate and shedding of winter coats were accelerated by applying extended photoperiod confirming that photoperiod affects more than just reproductive hormones.

Hoping to build on the current data, veterinarians from the Japanese Racing Association and Tokyo University placed 41 Thoroughbred yearlings under artificial lights to provide 14.5 hours of daily light from December 20th until April 15th. They measured body weight and fat-free mass throughout the extended photoperiod, comparing those measurements to 32 Thoroughbred yearlings maintained under natural lighting only. All horses were in northern Japan, in Hokkaido, a similar latitude as southern France and the Great Lakes in North America.

“One key finding of the study was that extending the photoperiod decreased the decline in growth rate in colts compared to those raised without lights, but the same effect was not seen in fillies,” said Ashley Fowler, Ph.D., a Kentucky Equine Research nutritionist.

Further, fat-free mass increased with age in both colts and fillies with the extended photoperiod, but the effect of extending the photoperiod on fat-free mass was more pronounced in colts than in fillies.

“These results support the idea that fat-free mass increases with longer day length. This may be a result of activating the hypothalamic-pituitary-gonadal axis and increasing circulating insulin-like growth factor-1 levels that play a role in muscle growth and development; however, further research is needed to elucidate those pathways more explicitly,” Fowler said.

Based on these results, artificial lights may be used in concert with modified training practices during the winter months to prepare young horses for competition as two-year-olds.

“To support increased muscle mass and training loads, bone density should also be considered. Triacton contains bioavailable calcium and other bone-building nutrients to help increase bone density in growing and exercising horses,” shared Fowler.

Read more: Extending Photoperiod for Muscle Development in Young Horses

By Juliet M. Getty, Ph.D.

Guidelines from Dr. Getty on feeding the horse in transition to domesticated

If there’s one thing we can say about the benefit of being wild (or feral, in healthful surroundings) is that in most circumstances horses which have been free to roam open lands are often healthier than domesticated horses. Think about their diet for starters—they have so much variety—grasses, flowers, berries, leaves, seeds, fruits—providing all the nutrients their bodies need. Once they leave this natural setting, however, they typically eat only hay and it’s the same hay every day. Hay is dead grass and no longer contains the vitamins found in their previous, varied diet. The horse’s nutrition gaps will need to be filled in order to match the rich nutrition of the wildenvironment. Therefore, to fill in the nutritional gaps:

• Provide a comprehensive vitamin/mineral supplement along with chia seeds and ground flaxseeds for omega 3s

  Horses in the wild rarely experience colic. One of the main reasons for colic in the domesticated situation is the rapid change from one feed to another, leaving the bacterial hindgut population little time to adjust. These microbes are responsible for digesting the fiber found in forage (hay and/or pasture) and need to be protected. To help your new horse’s digestive system adjust:

• Feed a potent probiotic that contains billions of colony forming units (CFUs)

  Ulcers are common in domesticated horses, especially when transitioning to a new environment. Horses are trickle feeders – they need to graze continuously to keep the digestive system functioning normally. That means they should have quality hay 24/7. Horses are awake and moving most of the time and will take 15 to 20 minute naps intermittently throughout the day and night. The best way to protect your new horse against an ulcer is to:

• Feed him in sync with his natural instinct to continuously graze by giving him hay, free-choice

  Many wild horses get adopted when they are young. They require the variety of feed sources that they had in the wild that offered quality protein, fat, vitamins, and minerals to support new growth. To accomplish this, add some alfalfa to your horse’s diet (about 30% of the total hay ration), along with either a supplement or a commercially fortified feed. Avoid cereal grains (oats, corn, etc.) and molasses – they can interfere with normal bone and joint development. In general:

• Feed growing horses extra protein, vitamins and minerals, chia seeds and ground flaxseeds to provide omega 3s, while avoiding high amounts of starch

  Respect your horse’s need to roam, along with other horses. Naturally curious, they enjoy seeking out feed in various locations, feeding their bodies, but also providing movement to keep the digestive tract muscles in good tone. And being prey animals, they depend on the companionship of other horses to protect them against threats, real and imagined. This transition phase can be stressful – new sights, smells, people, and other animals can create a hormonal response that can lead to a variety of health problems, including ulcers, colic, and laminitis. All of these can be avoided by making slow adjustments, filling in nutritional gaps, and doing as much as possible to simulate a natural setting. In other words…

• Feed him like he was meant to be fed – like a horse.

This article originally appeared on Getty Equine Nutrition and is published here with permission.

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