The objective of this study was to investigate the effect of acute and chronic heat load events on scrotal temperature (ST), body temperature (BT) and bull behaviour, and to examine the interrelationship between these parameters; the underlying hypothesis was that adverse heat treatments delivered in a temperature controlled environment will lead to thermoregulatory dysfunction of the bull scrotum. Six sexually mature Wagyu bulls were used in this study with data loggers surgically implanted into the abdominal cavity and scrotum. Body temperate and ST were recorded at 30-min intervals for the duration of the study. There were two housing locations used throughout the study, outdoor pens and climate control rooms. The study was designed as a four-phase crossover design with two heat treatments: (1) a 5-day acute challenge, and (2) a 14-day chronic challenge. The study was also blocked by phase to control for systematic change between phases with a thermoneutral (TN) phase in outdoor pens between each heat challenge. Observations within the climate rooms were conducted at 1-h intervals and data on panting scores (PS), respiration rate (RR), posture (standing or lying) and general behaviours (feeding, drinking, ruminating) recorded. Ambient temperature (AT, °C) and relative humidity (RH, %) were obtained at 10-min intervals and used to calculate the temperature humidity index (THI). Multiple models were conducted using a linear mixed effects model that contained different permutations of date and time factors and interactions as well as inclusion of an autoregressive parameter. The strongest model based on Akaike’s information criterion (AIC) was selected and further analysed. Ambient conditions during heat treatments were consistent with heat load and bulls showed typical physiological symptoms of the same. Maximum ST for acute and chronic treatments occurred once AT had exceeded 34 °C for at least 3 h (acute 35.59 °C at 1500 h; chronic 35.18 °C at 1400 h), whereas during TN conditions, maximum ST was at 2100 h. All phases showed variation in ST throughout the day. There were strong cross correlations between ST and RR during the heat treatments (acute r = 0.918, P < 0.0001; chronic r = 0.916, P < 0.0001), but not during TN (r = 0.411, P < 0.05). Our results confirmed that the ST of the bulls used in this study was not held at a constant temperature and that there was a possible connection between ST and RR. We have shown that during a period of heat load, the thermoregulatory mechanisms thought responsible for maintaining bovine ST appear to breakdown.

本研究的目的是调查急性和慢性热负荷事件对阴囊温度 (ST)、体温 (BT) 和公牛行为的影响，并检查这些参数之间的相互关系；潜在的假设是，在温度受控的环境中进行的不利热处理会导致公牛阴囊的温度调节功能障碍。在这项研究中使用了六头性成熟的和牛，数据记录器通过手术植入腹腔和阴囊。在研究期间，每隔 30 分钟记录一次体温和 ST。在整个研究过程中使用了两个住房位置，室外围栏和气候控制室。该研究被设计为具有两种热处理的四阶段交叉设计：（1）为期 5 天的急性挑战，(2) 14 天的慢性挑战。该研究还被阶段阻止，以控制每次热挑战之间室外围栏中的热中性 (TN) 阶段之间的系统变化。每隔 1 小时在气候室内进行一次观察，记录喘气分数 (PS)、呼吸频率 (RR)、姿势（站立或躺卧）和一般行为（进食、饮水、反刍）的数据。环境温度 (AT, °C) 和相对湿度 (RH, %) 每隔 10 分钟获得一次，用于计算温度湿度指数 (THI)。使用包含日期和时间因素和相互作用的不同排列以及包含自回归参数的线性混合效应模型进行多个模型。选择并进一步分析了基于 Akaike 信息准则 (AIC) 的最强模型。热处理期间的环境条件与热负荷一致，公牛表现出相同的典型生理症状。急性和慢性治疗的最大 ST 一旦 AT​​ 超过 34°C 至少 3 小时（急性 35.59°C 在 1500 小时；慢性 35.18°C 在 1400 小时），而在 TN 条件下，最大 ST 在 2100 小时。所有阶段全天都显示 ST 变化。在热处理过程中，ST 和 RR 之间存在很强的互相关性（急性 r = 0.918，1500 小时时 59 °C；在 1400 小时慢性 35.18°C），而在 TN 条件下，最大 ST 为 2100 小时。所有阶段全天都显示 ST 变化。在热处理过程中，ST 和 RR 之间存在很强的互相关性（急性 r = 0.918，1500 小时时 59 °C；在 1400 小时慢性 35.18°C），而在 TN 条件下，最大 ST 为 2100 小时。所有阶段全天都显示 ST 变化。在热处理过程中，ST 和 RR 之间存在很强的互相关性（急性 r = 0.918，P < 0.0001；慢性 r = 0.916，P < 0.0001），但不是在 TN 期间（r = 0.411，P < 0.05）。我们的结果证实，本研究中使用的公牛的 ST 没有保持在恒定温度，并且 ST 和 RR 之间可能存在联系。我们已经表明，在热负荷期间，被认为负责维持牛 ST 的温度调节机制似乎崩溃了。