Effects of an extended photoperiod on body composition of young Thoroughbreds in training.

This research examined the impact of extended daylight hours on the body composition of young Thoroughbreds in training, finding that such conditions could lead to increased growth in muscle mass.

Research Context and Methodology

• The study was conducted on seventy-three Thoroughbred horses (colts and fillies) in the Hidaka Training and Research Center under the aegis of the Japan Racing Association in Hokkaido.
• These horses were divided into two groups. One group of forty-one horses was exposed to an extended photoperiod (EP) from December through mid-April, while the remaining thirty-two horses were kept under natural light alone, serving as the control group.
• The study was undertaken from December when the horses were one year old until April when they were two years old.

Parameters and Measurements

• The parameters used to measure the horses’ body composition were body weight (BW), rump fat thickness (RFT), fat-free mass (FFM), and the percentage of fat (%F).
• The study aimed to discern changes in these parameters over the specified period and between the two groups of horses.

Findings and Conclusions

• The study found that in the group of colts exposed to an extended photoperiod, both body weight and fat-free mass increased with age.
• In contrast, among fillies, body weight increased with age in both groups (EP and control), but an increase in fat-free mass was observed only in the extended photoperiod group.
• Between December and April, colts in the extended photoperiod group showed a higher rate of increase in both body weight and fat-free mass than their counterparts in the control group.
• When compared to the control group, horses in the extended photoperiod group, irrespective of sex, exhibited a significantly higher rate of fat-free mass increase from January to March, specifically in March.
• These findings suggest that exposing young thoroughbreds in training to an extended photoperiod, especially in regions where winter days are shorter, can accelerate muscle growth. This could potentially be a beneficial technique to promote physical development in racehorses.