High-Starch vs Forage-Only Metabolomics in Athletic Horses

Six Standardbred geldings in active race training completed a crossover feeding study conducted near Uppsala, Sweden.

The horses were approximately 6.5 years old and had a mean initial body weight of 515 kg.

Two dietary periods of 29 days were used. Three horses began on each diet before crossing to the alternative diet. There was no washout period between dietary periods.

The forage-only diet consisted of early-cut grass haylage and supplied no dietary starch.

The forage-concentrate diet combined later-cut grass haylage with a concentrate containing 35.8% starch. The concentrate consisted primarily of oats together with soybean meal, wheat bran and sugar.

Actual daily starch intake averaged zero on the forage-only diet and 2503 ± 108 g per day on the forage-concentrate diet.

The horses remained in race training throughout the experiment and followed the same exercise protocol during both dietary periods.

After 25 days of dietary adaptation, postprandial plasma was collected for targeted metabolomic analysis. One forage-period plasma sample was unavailable.

The study used each horse as its own comparison, allowing metabolic profiles under the two dietary conditions to be examined within the same athletic horses.

Plasma samples were collected on day 25 of each dietary period after the horses had adapted to the diet.

On the sampling day, horses received a standardized meal and were then transported approximately 25 km to a clinic before blood collection. Samples were collected approximately eight hours after feeding.

Targeted proton nuclear magnetic resonance, or 1H NMR, metabolomics was used to quantify 52 plasma metabolites.

Individual metabolites were compared between diets using a linear mixed-effects model with horse included as a random effect and diet and period as fixed effects. P-values were adjusted for multiple comparisons using the false discovery rate method.

Partial least squares discriminant analysis was also used to examine the overall metabolic profile and identify metabolites that contributed most strongly to separation of the forage-only and high-starch diets.

Feed and nutrient intake were recorded so that metabolic findings could be considered alongside differences in starch, fibre, protein, energy and water-soluble carbohydrate intake.