SALIVA PRODUCTION IN CRIB-BITING AND NORMAL HORSES

C.A. McCall, B.A. Moeller, S.J. Silverman, and W.H. McElhenney

Increasing saliva flow to buffer the stomach or to flush the digestive tract has been hypothesized as a basis for crib-biting in horses. Saliva amount in 7 cribbing and 7 non-cribbing, control, horses was compared either pre- and post-cribbing or at a 5 minute interval for controls. A preweighed cellulose sponge was used to collect saliva at the exit of the submandibular gland for 30 seconds, then sealed in an airtight bag until reweighed. Saliva weight was measured between 1300 and 1500 h for three consecutive days for each horse. Data were analyzed as repeated measures. Mean saliva weight was similar between cribbing and control horses (1.2 and 1.5 g, respectively, S.E. = 0.2). However, mean saliva weight for pre and post samples (1.5 and 1.2 g, respectively, S.E. = 0.06) for all horses was different (P<0.05), indicating a drying effect of the sponge. Because of a strong tendency (P<0.06) for a treatment by sampling time interaction, data were analyzed by sampling time and cribbing status. Mean saliva weights in the pre sample were 0.43 g higher (P<0.03) in control than in cribbing horses indicating cribbing horses either produce less saliva or ingest saliva more frequently than normal horses. Control horses showed a 0.38 g decrease (P<0.01) in saliva weight between pre and post samples which was not evident in cribbing horses. To determine if cribbing behaviour offset the saliva decrease seen in control horses, 9 cribbing horses were sampled as before but were not allowed to crib between samples. A similar reduction (0.39 g, P<0.01) in saliva weights between pre and post samples was seen in these horses as was seen in control horses in the initial study, indicating that cribbing does compensate for the drying effect of the sampling procedure. Because cribbing horses had lower pre sample saliva weights than controls, these data do not support the hypotheses that cribbing produces enough excess saliva to buffer the stomach or to flush the GI tract. However, because cribbing does increase saliva production, gastrointestinal irritation could be a motivating cause for cribbing.

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