The principal focus of this study was to describe how the coat characteristics could affect the heat exchanges in animals managed in a hot environment. The Morada Nova ewes were monitored once a month, during 10 consecutive months, in three commercial flocks. Initially, an analysis was performed to measure the differences regarding the coat color in the thermoregulation mechanisms. The animals were grouped into 4 different groups according to coat tonality, as follows: dark red animals (group 1, N = 23), intermediate red color (group 2, N = 27), light red animals (group 3, N = 30), and white-coated animals (group 4, N = 30). The data were collected from 1100 to 1400 h, after the animals were exposed to 30 min of direct sunlight. The cluster analysis was performed considering the hair structural characteristics such as coat thickness (CT, cm), hair length (HL, mm), hair diameter (HD, m), and number of hairs (NH, hairs per unit area), after that these clusters were compared in relation to thermoregulatory mechanisms that include rectal temperature (RT, °C), respiratory rate (RR, breaths min−1), cutaneous evaporation (CE, °C), and respiratory evaporation (RE, W m−2). The groups were characterized and compared using mean and standard deviation, and the differences between the clusters were compared using the Tukey test with a 5% probability of error. In relation to coat color, no differences were found in groups 1, 2, and 3 regarding the activation of the thermoregulation mechanisms. The most different was observed in the totally white coat that presented different thermoregulatory responses as the highest sweating rate. White-coated animals showed a non-pigmented epidermis, and the hair structure is responsible to promote skin protection as necessary, such as a dense coat (1242.7 hair cm−2), long hair (14.2 mm), and thicker coat (7.38 mm). In red-coated animals, the hair structure favored heat loss to the environment, such as short hairs, less thick coat, and less hairs per square centimeter. All evaluated animals showed the rectal temperature within the reference limits for the ovine species, regardless of the coat color. In the analysis of clusters related to the physical structure of hair, it was possible to observe that the animals with thick hair, short hair, and less dense coat tended to have a higher capacity to eliminate heat through their respiratory rate and showed less intense heat loss by cutaneous evaporation. We verified that coat color presents a direct influence on the hair structure and the activation of mechanisms related to thermoregulation.

中文翻译：

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毛色和毛形态性状对毛羊耐热性相关机制的影响

这项研究的主要重点是描述被毛特征如何影响在炎热环境中管理的动物的热交换。Morada Nova 母羊在三个商业鸡群中连续 10 个月每月监测一次。最初，进行了一项分析以测量体温调节机制中毛色的差异。根据毛色将动物分为 4 个不同的组，如下：深红色动物（第 1 组，N = 23）、中间红色（第 2 组，N = 27）、浅红色动物（第 3 组，N = 30 ）和白毛动物（第 4 组，N = 30）。在动物暴露于直射阳光 30 分钟后，从 1100 到 1400 小时收集数据。聚类分析是根据毛发的结构特征进行的，例如毛发厚度（CT，cm），头发长度（HL，mm），头发直径（HD，m）和头发数量（NH，每单位面积的头发），然后将这些簇与包括直肠温度（RT，°C）在内的体温调节机制进行比较，呼吸频率（RR，呼吸分钟-1），皮肤蒸发（CE，°C）和呼吸蒸发（RE，W m-2）。使用平均值和标准差对组进行表征和比较，使用 Tukey 检验比较聚类之间的差异，误差概率为 5%。关于毛色，第 1、2 和 3 组在体温调节机制的激活方面没有发现差异。最不同的是在完全白色的外套中观察到的，呈现出不同的体温调节反应作为最高的出汗率。白毛动物表现出无色素的表皮，毛发结构负责根据需要促进皮肤保护，例如浓密的毛发（1242.7 毛发 cm−2）、长毛发（14.2 毫米）和更厚的毛发（7.38 毫米）。在红毛动物中，毛发结构有利于将热量散失到环境中，例如毛发短、被毛较少、每平方厘米的毛发较少。无论毛色如何，所有评估的动物的直肠温度均在绵羊物种的参考范围内。在与毛发物理结构相关的聚类分析中，可以观察到，毛发浓密、毛发短、被毛密度较低的动物往往通过呼吸频率具有较高的散热能力，并且表现出较少的强烈热量。皮肤蒸发损失。