This Is AuburnElectronic Theses and Dissertations

Reducing Cribbing Frequency in Horses Through Dietary Supplementation of Tryptophan and Calcium Carbonate




O'Reilly, Blaine

Type of Degree



Animal Sciences


Cribbing is an equine stereotypy that results in damage to both the horse and the facilities. Serotonin is a neurotransmitter that has calming effects on many animals’ behavior (Fernstrum, 1994). It has been shown that tryptophan is the precursor for serotonin and supplementing this amino acid will result in increased serotonin production (Fernstrum, 1994). The resultant mood change may calm the horse and lead to a decrease in cribbing activity. Some authors hypothesize that an acidic gastric pH will result in increased cribbing activity in horses (Nicol et al., 2002). Perhaps the supplementation of an antacid such as calcium carbonate will increase the pH of these horses and decrease their cribbing activity. The objectives of this study were two fold: first, to determine if either tryptophan or calcium carbonate supplementation would decrease the number of cribbing bouts per day, the number of crib-bites per bout, or the duration of each bout, and second, to determine if either supplement resulted in an increase in fecal pH, a gross estimate of gastric pH. Nine horses were utilized in a split-plot design in which the whole plot was designed as a replicated 3 x 3 Latin square with three replicates. The horse*period*treatment term was used as the error term to test for treatment differences. Each horse spent three weeks on each treatment: 3 g feed grade tryptophan mixed in 30 cc corn syrup, 42.5 g calcium carbonate mixed in 30 cc corn syrup, or 30 cc corn syrup control. Treatments were administered at 0700, 1100, 1500, 1900, and 2300 hrs. Each horse was observed on day 7, 14, and 21 of each treatment for a 17 h period. A washout period of 1 week was implemented between each treatment. There was no effect of treatment on fecal pH (P > 0.18), with values ranging from 6.4 + 0.1 to 6.8 + 0.1 over the three week test period. There was also no effect of treatment on the total number of cribbing bouts per day (P > 0.3), with values ranging from 48.7 + 6.1 to 72.6 + 6.1 over the three week test period. Similarly, there was no significant change of the average duration of each bout (P > 0.9), with these values ranging from 260.8 + 24.7 to 334.6 + 24.7 for the test period. Finally, there was no effect of treatment on the average number of crib-bites per bout (P > 0.8), with a range of 24.5 + 2.7 to 32.7 + 2.2 over the three week period. These results show that neither tryptophan nor calcium carbonate, at the given doses, will affect cribbing frequency or duration in horses.