The effects of abrupt dietary alterations on equine cecal pH

Abstract Text: Feeding starch in quantities exceeding 3.4 g/kg BW to the equine has been shown to exceed small intestinal capacity for digestion (Potter et al., 1992). This leads to fermentation of starch in the cecum resulting in a buildup of acidic products and decline in pH. Two consecutive 22 d experiments separated by 2 d of rest were conducted to identify whether abruptly feeding 1% (3.1 g starch/kg BW) and 1.25% (3.88 g starch/kg BW) BW concentrate during expt. 1 and 2, respectively, without hay would elicit a more profound decrease in cecal pH, as compared to the baseline diet. Nine cecally cannulated 8 to 10 yr old Quarter horses, 5 geldings and 4 mares, ranging in BW from 455 to 591 kg, were utilized. Baseline diets for both expt. consisted of 0.5% BW concentrate (Omolene 200, Purina Animal Nutrition, LLC, Gray Summit, MO; 1.55 g starch/kg BW) fed at 0700 and 1.5% BW native prairie grass hay divided into 2 feedings (0700 and 1930) for 21 d. On d 22 of both expt. the concentrate meal was increased to 1% (expt. 1) and 1.25% (expt. 2) BW and fed without hay. Cecal pH was measured from d 19 to 22 of both expt. at -1, +1, +4, +8, +12, +16, +20, and +24 h relative to feeding concentrate. ANOVA was performed with mixed models (SAS 9.3, 2011) and least square means compared using Fisher’s LSD (P<0.05, LSM ± SE). Complete randomization with either repeated measures (expt. 1) or a split-plot design (expt. 2) was utilized. In both expt. there was a time effect (P < 0.0001) on cecal pH. Expt. 1 cecal pH at +1 (7.2 ± 0.046) and +12 (6.8 ± 0.046) h on d 22 was decreased (P < 0.05) when compared to mean responses at +1 and +12 h during baseline feeding (7.4 ± 0.046 and 7.02 ± 0.046, respectively). In expt. 2 cecal pH was decreased (P< 0.05) only at +12 h (6.8 ± 0.041) on d 22 when compared to mean values at +12 h during baseline feeding (7.0 ± 0.041). Throughout both experiments, post-prandial cecal pH was characterized by a decline at +4 h, reached a minimum value at +8 h, and increased by +12 h. However, the primary variation between baseline and d 22 was a more rapid rise in pH from +8 to +12 h.

Keywords: equine, starch, cecal pH