Fibre Composition and Maturity of Forage-Based Diets Affects the Fluid Balance, Faecal Water-Holding Capacity and Microbial Ecosystem in French Trotters

Racing events challenge the fluid balance of athletic horses. The equine large intestine functions as a fluid reservoir, since the properties of dietary forage fibre affect the digesta water content and the milieu of this ecosystem. This study aimed to investigate the effect of grass maturity and legume forage on the faecal water-holding capacity (WHC) and microbial ecosystem, and the fluid balance and body weight (BW) of French trotters in race training. Six geldings were offered three diets with different fibre compositions: concentrate and late-harvested mature grass haylage (35:65 energy ratio) (CMGH); early-harvested grass haylage and mature grass haylage (80:20) (EGH); and lucerne and mature grass haylage (80:20) (LH), for 24 days in a Latin square design. Body weights were lower and faecal WHC higher when the horses were fed EGH compared to CMGH and LH (485 vs. 492 and 492 kg, p < 0.001; 12.6 vs. 11.1 and 11.4 g H₂O/g dry faeces, p = 0.014, respectively). Total water intake and output did not differ between diets, but water excretion via faeces was lower and via urine was greater on EGH compared to CMGH and LH (13.1 vs. 18.8 and 17.6 kg, p = 0.001; 10.5 vs. 7.6 and 7.9 kg, p = 0.032, respectively). Total bacteria concentrations were higher on EGH than CMGH and LH (5.4 × 10¹¹ vs. 2.8 × 10¹¹ and 2.8 × 10¹¹ CFU/mL, p = 0.018, respectively). Concentrations of butyrate were greater, and pH was lower when fed EGH compared to CMGH and LH (3.0 vs. 2.0 and 1.6 mmol/L, p = 0.034; 6.5 vs. 6.9 and 7.2, p = 0.005, respectively). In conclusion, forage harvested at an early stage of maturity could benefit athletic horses' fluid balance by providing a more available large intestine fluid reservoir without increasing BW.

Effects of Differences in Fibre Composition and Maturity of Forage-Based Diets on the Fluid Balance, Water-Holding Capacity and Viscosity in Equine Caecum and Colon Digesta

Horses are herbivores, and their hindgut functions as a fluid reservoir as forage fibre properties have great impact on the water content of digesta and the milieu in the ecosystem. Our objective was to compare the effect of grass fibre maturity and legume forage on the water-holding capacity (WHC) and viscosity of the equine hindgut and the body weight (BW) and fluid balance of horses. Three diets: concentrate and late harvested grass haylage (35:65 energy ratio) (C); early and late harvested grass haylage (80:20) (G); lucerne and late harvested grass haylage (80:20) (L) were fed to six caecum and colon fistulated horses for 28 days in a Latin-square design. Total water intake and BW were higher when the horses were fed Diet L, but the digesta WHC was higher when fed Diet G. Total water excretion (via faeces + urine) and the difference in total water intake-output was higher when fed Diet L. Viscosity, measured on centrifuged digesta fluid, did not differ between diets, but the individual colon data of one horse were higher. In conclusion, early harvested forage might be beneficial for the fluid balance of athletic horses providing a higher WHC of hindgut digesta without increasing BW. The importance of digesta viscosity in relation to equine diets needs further investigations.

Hydration status of horses performing endurance exercise: II. Evidence for a role of dietary fibre type, not oil supplementation

The equine large intestine has been suggested to serve as a water reservoir during prolonged exercise and may be influenced by dietary fibre source or length. At the same time, oil supplementation may result in performance and possibly hydration advantages. This study was designed to examine the effect of different fibre-based feeds, of similar particle size, on hydration status, with and without oil supplementation. Six two-year-old Arabian horses were randomly assigned to diets containing either chopped grass hay (G) or a 50:50 chopped grass hay: fibre-based chopped mix (GC) and either oil supplementation (approximately 5.7% crude fat in total diet) or no oil supplementation. Horses consumed each diet at least 21 d before completing a 60 km exercise test. Total body water, determined using deuterium oxide (D2O), was 66.1% of body mass and did not differ due to treatment. Horses consuming GC had greater (P<0.05) body mass at the start of exercise than those consuming G. Water consumption during the exercise test was greater in G than GC (P<0.01; 13.3±1.3 l, 10.9±1.3 l), as were packed cell volume (P<0.01; G 36.8±1.2%, GC 35.1±1.2%) and plasma aldosterone across all times (P<0.001; GC 0.79±0.11 pmol/l, G 1.48±0.11 pmol/l). The results suggest dietary fibre source may play a greater role in hydration status over 60 km distances than does oil supplementation. Core temperatures reported in this study were all similar to those reported in a previous study using a 50:50 long hay to chopped highly digestible fibre mix and lower than reported in previous studies using long stemmed hay or pasture suggesting the particle size or length of the fibre may have an influence and thus merit further investigation.