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pH fluctuations in the hindgut of horses relative to meal feeding
This study assessed changes of pH over time in the equine hindgut relative to meal feeding. Nine Quarter horses with cecal cannulae surgically inserted 4 years prior to the experiment were utilized. The group was comprised of 5 geldings and 4 mares, with ages ranging from 8 to 10 years old, and bodyweight between 455 and 590 kg. Horses were housed in heated individual stalls, with ad libitum access to water and white salt blocks. The horses’ diet consisted of 1.5% BW prairie grass hay and 0.5% BW concentrate (Omolene 200, Purina Animal Nutrition, LLC, St. Louis, MO), with the concentrate fed in the morning only (0700) and the hay divided into 2 daily feedings (0700 and 1930). Horses were maintained on this regimen for 3 separate 21-d periods. During the last 3 d of each period (d 19 to 21), pH was measured in cecal and fecal samples collected at -1, +1, +4, +8, +12, +16, +20, and +24 h relative to feeding of the concentrate meal. Cecal and fecal pH fluctuations over time were jointly modeled using a general linear mixed model. Hindgut pH dynamics relative to feeding differed between the cecum and the feces (P < 0.0001). In the cecum, a decline in pH (approx. 0.363 ± 0.03; lsmean±SEM) was observed as soon as 4 h after feeding (P < 0.0001). Minimum pH values in the cecum were recorded 8 h after feeding, and a return to baseline cecal pH was apparent at 20 to 24 h after feeding. In the feces, a smaller decline was observed (approx. 0.144 ± 0.044) but it did not become apparent until 8 h after feeding (P = 0.035). The minimum fecal pH was reached at 12 h after feeding (P = 0.0055); by 16 h after feeding, there was no evidence for differences from baseline pH (P = 1.00). These results suggest a maximum time lag in pH fluctuations of approximately 4 h between the cecum and the feces. It is necessary to note that more precise lag times could not be quantified with this study design, as measurements were taken every 4 h. Further research is needed to fine-tune predictive ability of fecal pH on cecal pH over time.
Keywords: cecal pH, equine, fecal pH