110 Fecal pH, dry matter and volatile fatty acids of horses grazing legume-grass mixed pastures

Abstract

Abstract Inclusion of legumes into grass pastures improves pasture quality while significantly decreasing the use of nitrogen (N) fertilizer. Changes in nutritive value of the pasture can affect gut microbiome and health. This study aimed to determine the effects of bahiagrass (Paspalum notatum) pasture intercropped with rhizoma peanut (RP, Arachis glabrata) on forage nutrient composition and fecal variables. Unfertilized bahiagrass (UNF) with no N fertilizer, bahiagrass with 120 kg N.ha-1 (FER), and bahiagrass intercropped with RP and 30 kg N.ha-1 (RP) pastures were evaluated using twelve mature Quarter Horses continuously stocked for 84 days in a randomized block design. Forage and fecal samples were collected every 28 days. Pasture samples were analyzed for nutrient composition by NIR, and fecal samples were analyzed for dry matter (DM), fecal fluid pH and volatile fatty acids (VFA). Data were analyzed using a repeated measure mixed model ANOVA and associations between variables were tested using Pearson’s correlations. Pasture starch was higher (P < 0.01) and non-fiber carbohydrates tended to be higher (P < 0.1) in RP. Hemicellulose and aNDF tended (P < 0.1) to be higher in UNF than in RP. Horses grazing RP tended (P < 0.1) to have greater fecal fluid propionic acid concentration and lower proportion of butyric acid. Proportion of acetic acid was lower (P < 0.05) in FER. Propionic acid concentration was negatively correlated with aNDF (r = -0.55) and ADF (r = -0.52), and positively correlated with ethanol-soluble carbohydrates (ESC, r = 0.55). Butyric acid proportion was negatively correlated with nonstructural carbohydrates (r = -0.70). Horses grazing FER pasture tended to have lower (P < 0.1) fecal DM when compared to RP. Fecal DM was negatively correlated with hemicellulose (r = -0.51), and positively correlated with water-soluble carbohydrates (r = 0.68) and ESC (r = 0.64). Intercropping RP provides pasture nutrient composition superior to UNF and similar to FER with decreased N fertilizer rate, and stimulates positive fermentation outcomes.