Effect of in utero exposure to hyperthermia on postnatal hair length, skin morphology, and thermoregulatory responses
This study investigated the effects of in utero heat stress exposure, specifically the last 2 months of gestation on postnatal skin, hair characteristics, and thermoregulatory responses. We hypothesized that in utero hyperthermia would trigger fetal skin and hair adaptations, such as reduced skin thickness and hair length with increased sweat gland size and number. These adaptations would prepare the calf for similar postnatal environments (i.e., heat stress) and aid in effective thermoregulation. Fetal exposure to hyperthermic conditions elicited distinctive hair coat and skin morphology changes in the offspring, including fewer sweat glands and longer hair coats. Consequently, prenatally heat stressed heifers had elevated core body temperature during the pre-weaning period, despite being exposed to the same postnatal environment as their in utero thermoneutral counterparts. Supplementary Data and Figures: Supplementary Figure S1. Diagram of measurements obtained from the skin tissue biopsies. Images were analyzed for stratum corneum thickness (A; green line), epidermis thickness (A; yellow line), sweat gland depth (A; orange lines, proximity to skin surface), sebaceous gland number and cross-sectional area (A; pink circle), and sweat gland number and cross-sectional area (A; blue circle). Stratum corneum cross-sectional area was measured with threshold alteration features, whereby the skin surface layer was highlighted red and selected for measurement (B). Sebaceous gland cross-sectional area was measured with the use of a freehand tracing tool but sweat glands were quantified with changing the thresholds of the image, whereby the glands were highlighted red and all selected for cross-sectional area measurement (C). Average sebaceous gland and sweat gland sizes were calculated by dividing the total cross-sectional area of all the glands in the image by the number of glands counted. Supplementary Figure S2. In utero treatment by day interactions for weekly measurements of skin temperature neck unshaved (A), skin temperature neck shaved (B), skin temperature rump unshaved (C), and skin temperature rump shaved (D) from postnatal day 7 to day 63, from calves which were either in utero heat stressed or in utero cooled during late gestation. Raw data were transformed when deemed appropriate and back transformed for visual representation. ** indicates significance (P ≤ 0.05). Data is graphed using the LSM ± SE of the interaction (treatment by hour).