In one of those chicken or the egg kind of quandaries, it is difficult to know if horses display oral stereotypies such as crib biting because of discomfort from gastric ulcers, or if the gastric ulcers develop secondary to crib biting. Previous studies suggest a causal link between crib biting and gastric ulcer syndrome (GUS), with speculation that as a form of self-medication, crib biting stimulates more saliva production to help buffer stomach acid.
A recent study looked at differences in the anatomy and physiology of the equine stomach in crib biting horses (CB) compared to non-crib biting (N-CB) horses [Daniels, S.P.; Scott, L.; De Lavis, I.; Linekara, A.; Hemmings, A.J. Crib Biting and Equine Gastric Ulceration Syndrome: do horses that display oral stereotypies have altered gastric anatomy and physiology? Journal of Veterinary Behavior (2019), doi: https://doi.org/10.1016/j.jveb.2018.12.010].
Cadaver stomachs were evaluated from 24 horses whose behavior prior to slaughter was noted as crib biting or not; wear on the central incisors confirmed CB or N-CB individuals. Gastrin cell quantification was performed on all the stomachs. Gastrin secretion occurs in response to feed and is not considered a stress hormone. In addition, 18 other cadaver stomachs provided information about stomach pH levels.
The researchers conclude that there is no anatomical or physiologic difference in gastrin cell concentration, stomach pH, or the mucosa of either the fundic or pyloric regions between cadaver CB stomachs and N-CB stomachs. Interestingly, gastric ulcers were identified in both CB and N-CB stomachs.
Crib biting behavior is likely a response to environmental stress, just as is gastric ulcer disease. They are probably separate clinical syndromes linked to environmental and cellular stressors, according to the authors of the study.
