Researchers know that diet can impact a horse’s metabolism. Recent studies have also confirmed that diet alters horses’ metabolic responses to exercise, especially when comparing all-forage diets with more traditional high-concentrate diet. However, it hasn’t been clear how transportation—an important factor, considering that performance horses are transported to competition venues on a regular basis—impacts metabolism. But researchers recently learned it could have a more significant impact than previously thought.
Researchers from the Wågen National Center for Education in Trotting and the Swedish University of Agricultural Sciences, both in Sweden, separated six trained adult Standardbred trotting mares into groups, in which they consumed one of two diets with similar calorie contents. One group consumed forage only (Group F, a timothy and meadow fescue haylage) and the other ate a 50/50 mix of the same forage plus oats (Group FO). The researchers also provided mares with a commercial vitamin and mineral mix, limestone, and salt daily. After a 29-day trial period and a three-day washout, the mares switched diets so that each consumed both diets.
On Day 21 of each study period, the researchers transported the horses for 100 kilometers before and after the mares performed an exercise test simulating a trotting race (the transport test, or TT). The mares did a second similar exercise test on Day 26 of each period but were not transported before or after (the control test, or CT). The team measured horses’ water intake and heart rates, along with collecting blood samples at various intervals pre- and post-exercise for 24 hours, before the first and after the second transport or at similar time points while CT horses remained in their stalls.
Regarding diet, the team found that:
- Horses in Group F had higher plasma acetate levels than those in Group FO; the researchers expected this finding as acetate is a product of fiber fermentation in the hindgut, and Group F horses consumed more hay than Group FO horses;
- However, immediately after exercise during the TT, acetate levels in Group F decreased, suggesting mares’ muscles used more acetate when they consumed the forage-only diet;
- During the TT, the researchers noted lower total plasma protein immediately after exercise and at ten minutes post-exercise in Group F mares compared to Group FO mares. This indicated the F mares had a greater plasma volume, which help improve performance.
- Group F mares drank more water on test days until 72 hours after exercise than did their Group FO counterparts.
However, the team found that transportation affected more metabolism parameters than diet in study mares, including:
- Transportation increased plasma glucose (measured immediately and at 10 minutes post-exercise), especially in FO mares. Previous research has shown that high plasma glucose levels during exercise are related to improved performance in horses;
- Transportation increased plasma cortisol levels before and after exercise in FO mares, but only after exercise in Group F mares. Researchers know that cortisol stimulates a rise in blood glucose and could be responsible for increased plasma glucose levels;
- Group F mares exhibited greater heart rates during transport and before and after exercise, while Group FO mares showed greater heart rates when transported after exercise only; and
- Nonesterified fatty acids rose significantly during the first and second transport in the TT compared to the CT. This suggests there could be fatty acid available for use as an energy source during exercise.
What Does it all Mean?
All those results indicate that transportation prior to exercise could impact horses’ performance.
“I was surprised that the relatively short transportation affected more metabolic parameters than the two very different diets,” said Malin Connysson, PhD, head of research and development at the Wången National Center for Education in Trotting. “In fact, transported horses consuming the forage-only diet showed indications of greater aerobic energy supply and less exercise-induced effects on extracellular fluid levels.”
In future studies, the team said, researchers should incorporate transportation into experimental designs to properly assess the real-world management practices of performance horses.
The study, “Road transport and diet affect metabolic response to exercise in horses,” was published in the Journal of Animal Science.