Effect of high-starch or high-fibre diets on the energy metabolism and physical performance of horses during an 8-week training period

Abstract

Large amounts of high-starch concentrates are traditionally fed to horses in training. However, this has been associated with digestive or muscle diseases and behavioural modifications. In parallel, it has been demonstrated that horses fed high-fibre, low-starch diets achieve the same performance over an exercise test as the ones fed high-starch diets. However, whether the same performance level can be maintained over a longer training cycle is still being determined. This study aimed to compare the evolution in physical performance and cardiorespiratory responses of two groups of French Trotters fed either a control high-starch (15.0 g dry matter hay/kg body mass/day + 6.6 g dry matter oats/kg body mass/day) or a high-fibre diet (75% of oats replaced by dehydrated alfalfa) over an 8-week training period. The horses that entered the trial were untrained for ≥4 months and previously fed hay only. Track training with speed monitoring included interval training sessions and 2400 m performance tests from week 1 to week 8 (W8). Before (week 0, W0) and after (week 9, W9) the training period, horses performed an incremental continuous exercise test during which cardiorespiratory parameters were measured. Both groups progressed to the same extent regarding physical performance measured during interval training sessions (acceleration: 0.16 m.s^-2 at W0 and 0.40 m.s^-2 at W8; p < 0.0001), the 2400 m performance test (average speed: 8.88 m.s^-1 at W0 and 10.55 m.s^-1 at W8; p < 0.0001), and the incremental continuous exercise test (speed during the fastest stage: 9.57 m.s^-1 at W0 and 10.53 m.s^-1 at W9; p = 0.030). Although oxygen consumption increased with training (p = 0.071), it was not influenced by the diet. On the contrary, carbon dioxide production increased in the high-starch group only (high-starch group: 84.0 vs. high-fibre group: 77.7 mL.kg^-1.min^-1 at W9; p = 0.031). The results illustrate that horses in both groups progressed similarly but did not use the same metabolic pathways during exercise. This hypothesis is supported by carbohydrate oxidation, which tended to increase in the high-starch group at W9 but decreased in the high-fibre group (p = 0.061). In conclusion, the substitution of high-starch by high-fibre diets enabled similar performance over an 8-week training period and altered energy metabolism in a way that could be beneficial during high-intensity exercise.

Keywords: French Trotters; VܩCO2; VܩO2; alfalfa; gas exchange; incremental test.

FIGURE 1

Repartition of training sessions, exercise, tests, and measurements throughout the study.

FIGURE 2

Changes in body mass, body condition score, and gluteus medius thickness during the 8-week training in horses fed a control diet or alfalfa diet. Mean values are reported. ^{a, b, c}Superscripts indicate different (p < 0.05) means between weeks.

FIGURE 3

Maximal peak speed (A) and acceleration (B) measured during the interval training sessions over the 8-week training (bold lines represent means, and individual values are represented in light); ^a;b;csuperscripts indicate different (p < 0.05) means between weeks.

FIGURE 4

Heart rate peak (A) and average speed (B) measured during the 2,400 m test over the 8-week training (bold lines represent means, and individual values are represented in light); ^a;b;csuperscripts indicate different (p < 0.05) means between weeks.

FIGURE 5

Average values (LSMeans and SEM) of $\dot{\mathrm{V}}{\mathrm{O}}_2$ , $\dot{\mathrm{V}}{\mathrm{C}\mathrm{O}}_2$ , and ratio between $\dot{\mathrm{V}}\mathrm{E}$ and $\dot{\mathrm{V}}{\mathrm{C}\mathrm{O}}_2$ during the incremental continuous exercise test depending on the speed stage in horses fed a control diet or alfalfa diet; *significant (p < 0.05) differences within the speed stage between weeks 0 and 9.

FIGURE 6

Average values (LSMeans and SEM) of carbohydrate and lipid oxidation during the incremental continuous exercise test depending on the speed stage in horses fed a control diet or alfalfa diet.