Histomorphometry of the placental vasculature and microcotyledons in Thoroughbred mares with chronic laminitis

- Mares with chronic laminitis had a shorter gestation length compared to healthy mares.
- Chronic laminitis was associated with a reduction in placental and fetal weight at term.
- Histomorphometry of the vasculature of the term placenta revealed differences between laminitic and healthy mares.

The objective of this study was to assess the placental vasculature and microcotyledons in pregnant mares with chronic laminitis. Twenty-six pregnant mares were enrolled in the study, 13 had chronic laminitis (Laminitis Group) and 13 were healthy mares (Healthy Group). Arterial systolic pressure and heart rate were measured in the last 30 days of gestation. After foaling, the fetal membranes were grossly evaluated and samples were harvested for histopathologic examination. All mares had digitalized images taken from chorioallantois for histomorphometry analyses (software-NIH ImageJ). Images were assessed for: (i) arterioles from the allantoic region: total and lumen vascular diameter and vascular wall thickness; (ii) microcotiledonary and capillary area/field. Mares in the Laminitis Group showed hypertension, shorter gestational length, lower placental weight and lower birthweight (p < 0.05) foal in comparison with mares in the Healthy Group. Laminitis mares had a reduction of vascular lumen diameters in the uterine body and pregnant horn (p < 0.05), vascular wall thickening in the pregnant horn (p < 0.05) and smaller capillary area/field in the microcotyledons of uterine body and pregnant horn (p < 0.05). In conclusion, pregnant mares with chronic laminitis presented signs of hypertension syndrome, and vascular abnormalitities in placental vessels such as reduction in the vascular lumen and capillary area in the microcotyledones, and thickening of the vascular wall. Foals born from mares with chronic laminitis showed lower birth weight and shorter gestation lengths.