COMPARISON OF GASTRIC pH IN CRIB-BITING AND NON CRIB-BITING HORSES

H.C. Lillie, C.A. McCall, W.H. McElhenney, L.N. Garcia, J.S. Taintor, J. Schumacher and S.J. Silverman

Gastrointestinal irritation has been hypothesized as a basis for crib-biting in horses. Gastric pH was compared in seven cribbing and seven non-cribbing (control) horses in phase I. Horses were fasted for 12 h then a small nasogastric tube fitted with a stainless steel strainer at the end was inserted into the stomach. After the initial sample, horses were given their usual sweet feed ration and gastric fluid samples were taken every 30 min for 5 h. A digital pH meter was used to determine pH of gastric fluid suctioned through the nasogastric tube. After sampling, gastric fluid was returned to the stomach via the nasogastric tube. Data were analyzed as a t-test. Gastric pH of the cribbing horses was lower (P< 0.05) than the control horses (3.4 and 5.5, respectively, S.E.D.= 0.9) in the initial sample, indicating that cribbing horses had a more acidic gastric environment than normal horses after fasting. Analysis of the remaining samples showed that a mean gastric pH of cribbing horses remained lower (P< 0.5) than controls when horses were fed (4.2 and 5.6, respectively, S.E.D. = 0.05). However, the variance in the cribbing horses was greater (P < 0.05) than in controls indicating that gastric fluid of cribbers had a wider pH range than that of controls after feed consumption. It is hypothesized that the wider range of pH measurements in the cribbers may be related to the amount of cribbing performed by the individual horse. In phase II, eight cribbing horses were used to determine if cribbing behavior influenced gastric pH. Gastric fluid sample collection and pH determination procedures were identical to those used in phase I except that samples were taken every 30 min for 1.5 h. The pH levels from horses when they were allowed to crib freely were compared to levels after they were prevented from cribbing for 2 wk. A commercially available cribbing collar was used to prevent cribbing. Data were analyzed as a t-test. Initial gastric pH samples were higher (P< 0. 03) when horses were not permitted to crib then when allowed to crib (4.4 and 2.8, respectively, S.E.D. = 0.39) indicating that when crib-biting is prevented fasting gastric pH values were increased. Mean pH of the remaining two samples also differed (P> 0.05) when horses were prevented from cribbing or allowed to crib (5.0 and 3.3, respectively, S.E.D.= 0.55). Results clearly indicate that cribbers have a more acidic gastric environment than normal horses supporting the theory that gastrointestinal irritation may be a motivating cause for cribbing. However, cribbing behavior itself may lead to a lower gastrointestinal pH. Preventing cribbing may increase gastrointestinal pH to a level comparable to that of non-cribbing horses.

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