Introduction:
Equine colic is a multifactorial syndrome, and horse owners frequently relate its occurrence to lunar cycles. Despite the popularity of this belief, scientific data are scarce. This study evaluated whether lunar phases are associated with the frequency of colic episodes in horses and whether they influence colic localisation or clinical outcome.

Methods:
A retrospective analysis was performed using clinical records of horses presenting with colic to a university large animal clinic between 2013 and 2020. Each case was assigned to one of four lunar phases based on the date of onset: new moon, last quarter, first quarter, or full moon. In total, 138 colic episodes with complete data were included. Statistical analyses were carried out in SPSS. A chi-square goodness-of-fit test was used to compare the observed distribution of colic cases across lunar phases with an equal expected distribution. Associations between lunar phase and localisation of colic or disease outcome were examined using chi-square tests of independence. Effect size was estimated using Cohen’s w.

Results:
Colic cases were not evenly distributed across the lunar phases: new moon n=50; last quarter n=39; first quarter n=20; full moon n=29 (χ²=14.52, df=3, p<0.01, w=0.32). Thus, colic episodes occurred significantly more often around new moon and the last quarter than during the first quarter. No significant association was found between the lunar phase and anatomical localisation of colic (p>0.05) or clinical outcome (p>0.05).

Conclusions:
Lunar phases showed a moderate but statistically significant association with the timing of colic episodes, with peaks around new moon and the last quarter. However, moon phases did not affect the type of colic or its outcome. Further prospective studies are needed to clarify underlying mechanisms and to control for management and environmental confounders.