Changes in equine hindgut fermentation and carbohydrate digestion in response to varying sources of nitrogen

Abstract Text:

Casein or urea were administered as dietary N sources in a replicated 3 x 3 Latin square experiment to evaluate impact on hindgut fermentation and carbohydrate digestion in the horse.  A basal diet consisting of native prairie hay (5.9% CP; 72.7% NDF) was fed to 9 cecally cannulated horses (469 ± 109 kg BW) at 0.6% of BW DM basis every 8 h for 6 wk.  Periods consisted of a 7-d acclimation to the basal diet and a 7-d dosing phase.  Horses were dosed via the cecal cannula 3x/d at the time of feeding for 7 d with 200 mL of water (W), or with 200 mL of water containing casein (C) or urea (U) to provide 1.12% N in the diet.  During the final 4 d of each dosing phase, total fecal output was collected and cecal digesta was collected 4 h after each feeding.  Cecal digesta and feces were analyzed for pH and concentrations of ADF, NDF, ADIA, total VFA, and ammonia.  Dosing with U resulted in greater concentrations of cecal ammonia (3.00 mM, P < 0.05) compared to horses dosed with W (1.69 mM), or C (2.01 mM).  Cecal pH increased (P < 0.01) in horses dosed with C (7.72) or U (7.85) compared to W (7.45), but fecal pH was not different between treatments (P > 0.05).  Total VFA concentrations in cecal digesta were greater (P < 0.01) for horses dosed with U (50.27 mM) compared to those dosed with W (32.17 mM) or C (32.17 mM).  Fecal NDF and ADF were decreased (P < 0.05) in horses dosed with U (63.07% NDF, 52.78% ADF) or C (59.68% NDF, 49.98% ADF) compared to those treated with W (66.50% NDF, 54.49% ADF), but ADIA content was not different (P > 0.05).  Taken together, differences in cecal ammonia, pH and total VFA, along with changes in fecal NDF and ADF as a result of treatment indicate that protein and non-protein N sources introduced directly into the cecum lead to changes in microbial fermentation in the hindgut that increase fiber digestion in the horse.

Keywords: equine, fiber digestion, nitrogen