Senior clinical teacher University of Helsinki, Finland University of Helsinki, Uusimaa, Finland
Abstract:
Background: Anecdotally, mares are at increased risk of laminitis during estrus; however, data on estrous cycle-related changes in blood insulin concentration are limited. Hypothesis: Serum basal insulin varies depending on estrous cycle phase Animals: 10 healthy, non-pregnant riding school mares
Methods: In this prospective cohort study, serum for basal insulin concentration was collected from each horse 9 times weekly (median number of days between samplings 7, range 5-15) during spring 2024. The estrous cycle was monitored on the same days using rectal examination and ultrasonography and categorized as estrus (follicles >25 mm and endometrial edema) or diestrus (corpus luteum, no endometrial edema). Serum insulin concentration was analyzed with a commercial equine-optimized ELISA (Mercodia equine insulin ELISA). Insulin values during and after the first ovulatory estrus were included in the statistical analysis.
Results: Serum basal insulin concentration varied within the horses. The median insulin concentrations in estrous and diestrous phases were 22.5 (min-max 6.8-87.5) µIU/mL and 15.2 (min-max 2.4-55.3) µIU/mL, respectively, and there was no difference between the phases (p=0.397). One horse was classified as having insulin dysregulation (insulin > 71 µIU/mL) in one estrus sample and insulin concentration in the equivocal zone (49-70.9 µIU/mL) in another estrus sample. Two other horses had insulin concentration in the equivocal zone in one diestrus sample. None of the horses had signs of laminitis. Conclusions and Clinical Importance: The estrous cycle phase was not associated with changes in serum basal insulin concentration. Therefore, the estrous cycle phase may not predispose mares to laminitis.
