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).

本研究探究了宫内热应激（in utero heat stress）暴露——尤其是妊娠最后两个月——对犊牛产后皮肤、毛发特征及体温调节反应的影响。本研究提出假说：宫内高热暴露将诱发胎儿皮肤与毛发的适应性改变，具体表现为皮肤厚度降低、毛发长度缩短，同时汗腺体积与数量增加。此类适应性变化可使犊牛更好地适应产后类似的热应激环境，助力其实现有效的体温调节。研究结果显示，胎儿暴露于高热环境后，其后代会出现独特的被毛与皮肤形态改变，包括汗腺数量减少、被毛长度增加。尽管产前热应激处理的小母牛与宫内热中性环境对照犊牛处于相同的产后环境中，但前者在断奶前阶段的核心体温显著升高。

补充数据与图表：
补充图S1：皮肤组织活检测量指标示意图。对采集的图像进行分析，测量指标包括角质层（stratum corneum）厚度（A图中绿色线条）、表皮（epidermis）厚度（A图中黄色线条）、汗腺深度（A图中橙色线条，即腺体与皮肤表面的距离）、皮脂腺（sebaceous gland）数量与横截面积（A图中粉色圆圈）以及汗腺（sweat gland）数量与横截面积（A图中蓝色圆圈）。角质层横截面积通过阈值调整特征进行测量：将皮肤表层标记为红色并选中以完成量化（B图）。皮脂腺横截面积采用自由手绘追踪工具测量，而汗腺则通过调整图像阈值进行量化：将腺体标记为红色，选中所有腺体以测量其横截面积（C图）。平均皮脂腺与汗腺体积通过将图像中所有腺体的总横截面积除以计数的腺体总数计算得到。

补充图S2：妊娠后期分别接受宫内热应激或宫内降温处理的犊牛，在产后7日至63日期间，颈部未剃毛皮肤温度（A）、颈部剃毛皮肤温度（B）、臀部未剃毛皮肤温度（C）与臀部剃毛皮肤温度（D）的周度测量值中，宫内处理与日龄的交互效应。原始数据在必要时进行数据转换，并通过反变换得到可视化结果。**表示差异具有统计学意义（P ≤ 0.05）。图表以最小二乘均值（Least Squares Means，LSM）±标准误（Standard Error，SE）的交互效应（处理×小时）进行绘制。