猪舍环境

The Environment in Swine Housing

猪舍环境

Author作者

Steven J. Hoff, Iowa State University

译者：高岩

Introduction引言

Economies of scale and the greater need for efficiency have resulted in the vast majority of pigs being raised indoors. These artificial environments have a great impact on production performance and the health status of both the pig and the worker. With the pork industry becoming more integrated, uniformstyle barns are built in multiples, and an error in design can be multiplied many times over. This situation highlights the continued need for adhering to basic design principles in ventilation and environmental control.

规模经济和对效率的巨大需求使得生猪养殖多为室内养殖。室内人工环境对生产成绩，生猪及养殖人员的健康状况有很大的影响。随着养猪行业愈发一体化，统一式样的猪场成倍增加，而设计上的的不合理之处则各不相同。在这种情况下，为了更好的掌控猪场的通风和环境状况，在猪场建设中，更加需要我们长期遵循猪场建设的基本设计原则。

The environment surrounding the pig is a complicated influence that is often difficult to assess. For example, studies have shown that pigs can be subjected to very high levels of ammonia for a relatively long time with little adverse production effect. However, adding dust, other gases, and humidity with high ammonia is a potentially disastrous combination. The synergistic effects of gases and dust are complicated and potentially very serious for the health status of not only the pig but of the workers as well. This report summarizes the requirements of the thermal environment, assessing the thermal environment, the economics of maintaining optimal thermal environments, and best management practices to achieve these environments.

生猪生存的环境异常复杂，人们对其往往很难把握。例如，研究表明，虽然在相对长的时间里，猪易受高浓度氨气的影响，但猪的生产量不会因此受到很大影响。然而，如果将高浓度氨与灰尘，其它气体，以及湿度混合起来，对猪的生产量的影响就可能是灾难性的。各种气体与灰尘相混合，情况会变得非常复杂，对猪及养殖人员的健康状况具有潜在的，重要的影响。本文总结了对猪热环境的需求，热环境的评估，保持热环境的经济学意义，并提供了实现这种热环境的最好的方法。

The Adaptability of the Pig猪的适应性

The pig is very adaptive to its environment, which is one of the complicating factors that often prevents a producer from recognizing potential problems. However, in many cases, adaptive

responses to the environment take feed energy away from growth and use it to fuel the adaptive response. For example, shivering is a response to combat cold stress by generating internal heat via muscle friction. This reaction often goes unnoticed; and while it is occurring, the pig is wasting feed energy to frictional losses that would otherwise go to growth.This adaptive response, multiplied by hundreds of pigs under one roof, can make a substantial difference in profitability.

猪具有很强的适应性，这种适应性使养殖人员难以识别猪群可能存在的问题。在很多情况下，出于对环境适应性的反应，猪群会将食物能量用于激发自身的这种适应能力，而不再将这些能量用于生长。譬如颤抖。这种反应通过肌肉摩擦产生内部热量来抵御寒冷。人们往往会忽视这种反应。为了抵御寒冷，这种反应使猪将本该用于生长的食物热量用在了摩擦损耗上。同一猪舍里的上百头猪的适应反应效果翻倍，使猪场收益显著不同。

What Constitutes the Pig’s Thermal Environment?什么组成了猪的热环境？

The thermal environment for the pig involves all factors that affect energy exchange between the pig and its surroundings. Energy exchange, in the form of heat, is transferred between the pig and its surroundings by four basic methods of heat transfer: conduction, convection, radiation, and evaporation. Conduction, convection, and radiation are grouped into sensible heat, which implies that a temperature difference is required to exchange heat by these methods. This temperature difference is between the pig’s core, or surface, and the surrounding surfaces (conduction and radiation), or the surrounding air (convection).Evaporation is a method of transferring large amounts of heat by the exchange of moisture between the surrounding air and the pig’s respiratory tract (i.e., breathing) or the pig’s surface during sprinkling events. Understanding how pigs lose or gain heat energy is a key to understanding the interaction between the pig and its environment. More detail on these methods is described below.

猪所处的热环境包含影响猪和其周围环境进行热量交换时的所有要素。猪和其周围环境以热的形式进行能量转换。转换方式有四种：传导，对流，辐射和蒸发。传导，对流和辐射属于可感知的热量，这意味着用这些方式交换热量需要提供温度差。这种温度差存在于猪的体内或体表与周围环境之间（如传导和辐射），或存在于猪的体内或体表与周围空气之间（如对流）。蒸发是指当人们给猪冲水时，猪的呼吸道，体表与周围空气通过交换湿度来转换大量热量的方法（例如呼吸）。了解猪怎样损耗或获取热能量是了解猪及其周围环境间相互作用的关键。关于这些方法的更多细节描述如下。

Conduction. This method of transferring heat occurs as a result of the pig being in physical contact with another surface with a temperature that differs from the core temperature of the pig. A pig, with a core temperature of about 103°F, lying on a concrete floor with a temperature of 70°F loses heat to the floor with an overall temperature difference of 33°F. Heat is conducted from the pig to the floor by traveling through the pig’s tissue and then to the concrete. The major components that affect the rate of conducted energy are the core-to-floor temperature difference, the conductivity of the floor and pig tissue, and the contact area between the floor and the pig. A standing pig loses very little heat to the floor via conduction compared to a laying pig because the contact surface area is very small in comparison. Pigs may actually use this to their advantage by adjusting the amount of contact they have with the floor, by sprawling to make a lot of contact

when they are too hot.

传导：当猪的身体接触到与其体内温度有温度差的其它物体表面时，就会出现这种热量转换方式。一头猪的体内温度大约为103°F，若它躺在温度为70°F的水泥地面上时，体温就会下降大约33°F。这些热量通过猪的肌肉组织，转移给水泥地面。影响能量的传导率的主要因素有：猪体内—体表温度差，地面的导热性，猪的肌肉组织传热性，以及猪与地表的接触面积。一头站立的猪和一头躺卧的猪相比，站立的猪通过热传导失掉的热量要少，这是因为站立的猪与地表接触面积很少。事实上，猪能充分利用此优势来调整它们与地表的接触面积。当它们感觉热时，会躺卧来增大与地表的接触面。

Convection. This method of transferring heat occurs as a result of the pig being in physical contact with air or mud or water at a temperature that is different than the core temperature of the pig. Technically, the temperature difference for this method of heat transfer occurs between the pig’s surface temperature and the surrounding fluid. But ultimately the pig’s surface temperature is dictated by the pig’s core temperature and the resistance to conduction heat transfer of the pig’s tissue components. The major components that affect the rate of convection energy are the surface-to-fluid temperature difference, the speed of the fluid, and the contact area between the pig and the fluid. This method is employed when fans are used to blow air on the pigs to reduce heat stress. Cold drafts are a negative example of convection.

对流：当猪的身体接触到与其体内温度不同的空气，泥土，水等物质时，会产生这种热量转移形式。学术上，此热量转换方式是指在猪的体表温度和其周围流质间产生温度差，从而使热量得以转换。但最终猪的体表温度受其体内温度的支配，并且抗拒肌肉组织成分的热传导转移。影响能量的对流率的因素有：体表—流质温度差，流质的流速，猪与流质的接触面积。我们给猪吹风扇使其降温就采用了这种方法。冷风直吹则不是很好的对流方法。

Radiation. This method of transferring heat is by far the most complicated method to describe accurately. Radiation heat transfer occurs as a result of the pig “radiatively seeing”surfaces at a temperature that differs from the pig’s surface temperature. For example, if a pig is standing in a pen, in a curtain-sided barn, and if the curtain is at a temperature lower than the pig’s surface temperature, the pig will lose heat radiatively to this curtain. This same principle applies to all surfaces that the pig radiatively sees. The major components that affect the rate of radiation heat transfer are the pig’s surface exposure to all other surfaces in the barn, the thermal reflective properties of the pig and all other surfaces, and the amount of area from the pig that radiatively sees every other surface in the barn. Radiation heat transfer can easily account for 50% or more of the total heat lost (or gained) by the pig. An example of this is a person standing in front of a large window during the winter. Even though the air is warm, they lose heat, and therefore feel cold because of being exposed to the cold window surface.

辐射：这种热转移方法是目前最复杂，最难准确描述的。当猪体表“辐射区域”温度不同于猪体表温度时，会发生这样的热转移。例如，一头猪站在猪舍有窗帘一侧的围栏里，如果窗帘的温度低于猪体表温度，猪就会将一部分热散发给窗帘。同理，猪也可散发热量给它附近任何可及的物体表面。影响猪辐射热转移率的的因素有猪体表暴露于猪舍物体的程度，猪和所有物体的热反应性能，以及猪的辐射区域与其它物体的可辐射面积。辐射热转移可以

很容易的使猪转移走（或获得）50%甚至更多的热量。我们可以举个例子，冬天一个人站在窗户前，此时即使室内温暖，人也会感到寒冷，因为人的身体暴露于较冷的窗体表面，会损失部分热量。

Evaporation. This method of transferring heat occurs as a result of water conversion to a vapor. The amount of energy required to accomplish this conversion is called the latent heat of vaporization. For water, approximately 1000 Btu of energy are required to evaporate one pound of water. Therefore, for every pound of liquid water that is evaporated from the pig’s respiratory tract, 1000 Btu of energy from the pig are exhaled with the vapor and added to the surrounding room. Likewise, properly controlled sprinkler systems can be used to provide an artificial sweating mechanism for pigs. The major components affecting the rate of evaporation heat transfer are the water vapor content (or relative humidity) and temperature of the surrounding air, the speed of air moving over the wetted portion of the pig, the wetted surface area, and the volume of air respired by the pig in time. As the air and surface temperatures surrounding the pig get closer to the pig’s core temperature, evaporation heat transfer becomes the only method that pigs can use to lose heat and therefore sustain life.

蒸发：这种热转移源于水向蒸汽的转化。水转化为水蒸气所需的能量值叫做水的潜性热蒸发。蒸发每磅水，大约需要1000 Btu的热能。因此，猪的呼吸道每蒸发一磅液态水，就要消耗1000 Btu 的热能，才能使这些水转化为水蒸气。我们可以使用合理操控的洒水系统为猪提供一个人工的出汗机制。影响蒸发热转移率的因素有：水蒸气含量（或称作相对湿度），四周气温，猪被打湿部分，周围空气的流速，打湿面积以及猪在一定时期的空气吸入量。当气温与猪体表温度接近时，蒸发热转移便成为使猪散热得以生存的唯一方法。

What Is an Optimum Thermal Environment for Pigs?什么是最佳热环境？

An optimum thermal environment for a pig is an environment that does not require an extraordinary response by the pig to maintain a constant core temperature. This is a complicated way of saying that the pig, being warm blooded, is always in a mode of sustaining life. Life is sustained in one major way by keeping core temperature constant. If the thermal environment is cold, the pig responds by huddling, shivering, redirecting blood flow to the core, or excessively eating because too much thermal energy is lost to the environment. To make up this difference, more energy is needed, or needs to be conserved. Likewise, a thermal environment that is hot invokes heat loss increasing mechanisms such as panting, lying spread out on cool floors, wallowing in mud, and suppressed eating, to name a few. These responses to cold and hot are all extraordinary measures required by the pig to maintain a constant core temperature. All imply that an optimum thermal environment does not exist.

在最佳热环境里，猪不需要对环境做特别的反应就可持久地保持体内核心温度。最佳热环境是较为复杂的说法，说明猪总是保持体内温暖来维持生命，主要方式是保持体内温度的持久恒定。如果一个热环境里温度较低，猪就会作出挤作一团，颤抖，血液流回心脏，或是进食量增大的反应。这是因为猪御寒损耗了大量的热能。为了弥补损耗的热量，就需要补充或储存更多的能量。同样地，如果一个热环境里温度较高，就会触发猪增大热量转移的机制。猪会作喘气，四肢伸展躺在地面上，打泥，进食量减少等等反应。猪的这些对冷和热的反应都

是保持恒定体温所必须的，所有这些意味着最佳热环境并不存在。

The previous examples referred to cold and hot. Temperature is only one thermal factor contributing to a cold or hot thermal environment. For example, an air temperature of 60°F is considered very good for 150 lb. pigs. However, this air temperature, combined with a 100 feet per minute air flow would actually be considered cold since the pig’s convection heat loss to the environment is high, requiring energy conservation measures to maintain a constant core temperature. One must be very careful when assessing the pig’s thermal environment. All factors that affect energy exchange with the thermal environment must be assessed to arrive at the proper conclusion.

前面的例子涉及到冷和热的问题，构成一个冷的或热的热环境的要素有很多，温度只是其中一个。例如，60°F的气温对于一头体重150磅的猪很合适，但同样60°F的气温，如果空气以每秒100英尺的速度流动，猪就会觉得冷。因为此时猪的对流热损耗很大，需要储存能量来保持体温恒定。所以，当我们评估猪的热环境时，必须非常谨慎。只有评估猪与热环境交换时所有的影响因素，才能得到合理的热环境值。

Measurements To Assess the Thermal Environment评估热环境的方法

The most important, most obvious, and easiest measured environmental factor is air temperature. Air temperature, relative to pig temperature, determines the level of energy exchange between the pig and its surroundings by convection and evaporation and indirectly through radiation. Air temperature is most easily measured with standard mercury bulb thermometers or digital-based sensors.

很明显，最重要，也是最容易的估算环境因素的方法是气温。相对于猪的体温，气温决定了猪通过对流，蒸发和间接地辐射与周围环境进行能量交换的程度。用汞柱气温计或数字传感器很容易测得气温。

Second, the speed of air moving over pigs is another important factor. Air flow directly affects both convection and evaporation methods of heat transfer. Air flow can be measured with either digital-based sensors or simple vane or paddlewheel sensors.

第二，测量空气流速。空气流速直接影响了对流热转移以及蒸发热转移。测量空气流速，可以用数字传感器，简易风向标或明轮传感器。

Third, the surrounding surface temperatures are critical indicators of a pig’s thermal environment. Surface temperatures in contact with the pig affect conduction heat transfer and surface temperatures surrounding the pig affect radiation heat transfer. Surface temperature measurements can be made by an infrared thermometer and are a little more difficult and expensive to make, but nevertheless a critically important indicator.

第三，周围物体的表面温度也是热环境的重要指示物。与猪身体相接触的物体表面温度影响传导热转移，猪四周的物体表面温度影响辐射热转移。物体表面温度可用红外线气温

计测得。虽然测量物体表面温度非常困难，而且造价很高，但却是一个非常重要的参考。

Fourth, the water vapor content of the surrounding air, combined with air temperature, directly affects the evaporation of liquid water. A device called a psychrometer can be used to determine the actual water vapor content of the air. A measurement of relative humidity is, as the name implies, a purely relative measurement and does not directly define the actual water vapor content of the air.

第四，空气的水汽含量及气温直接影响液态水的蒸发。干湿球相对湿度计可用来测量空气中的水汽含量。相对湿度的测量，正如其名称中暗指的，仅仅是种相对的测量，这种测量不能直接测得空气中实际的水汽含量。

The Effective Environment of the Pig猪的有效环境

The term Effective Environmental Temperature (EET) has been used for many years by researchers and academicians and has recently found its way into the pig industry. The EET refers to the combined influences of many environmental factors that define the level of energy exchange between the pig and its surroundings. For example, a pig exposed to 70°F temperature with low air flow is being subjected to a very different thermal environment than a pig exposed to 70°F temperature with high air flow. The effective environment for the pig in high air speed is much cooler because the pig is losing more heat to its surroundings via convection. This is similar to the term “wind chill”used in giving winter weather reports. Likewise, if we compare two barns, maintained at the same air temperature, both with low air flow, with one of the barns having little or no wall insulation, each will “thermally”affect the pig in a very different way. With little wall insulation, pigs will radiatively “see”cold walls during the winter and thus their effective environment will be cooler, represented by a lower EET.

很多年以前，研究者和学者就已使用了有效环境温度（EET）这个词。最近，猪养殖行业也开始引用这个词。有效环境温度指决定猪及其环境间能量转换程度的各种环境影响因素。例如，在70°F空气流动速度慢的环境中的猪和在70°F空气流速快的环境中的猪，会受到非常不同的热环境影响。猪在空气流速快的有效环境中会更冷，因为此时通过对流猪会损失更多的热量。这类似于冬季播报天气时使用的“风寒”。

同样，如果我们对比两个猪舍，假如它们保持相同气温，空气流速都较慢，其中一个猪舍极少或没有墙壁进行隔离，那么这两个猪舍在热量上对猪会有不同的影响。当极少有墙壁隔离时，猪在冬季会辐射性“感知”到较冷的墙体，这样其有效环境会较冷，其有效环境温度值就低。

The EET is convenient (put into “temperature”terms) and easily understood. The specific methods used to calculate EET are complicated and beyond this discussion, but the concept is important. The most important thing to remember is that the comfort and performance level of the pig is directly influenced by how readily (or unreadily) the thermal environment takes (or gives) energy in the form of heat to (or from) the pig. If the air temperature is below the core temperature of the pig, then a hot, still environment has a higher EET than a hot, high air speed environment. However, if the air temperature is above the core temperature of the pig, then the barn with the

lower air speed will have a lower EET. Why? Because if the air temperature is above the core temperature of the pig, then a higher air speed will force heat into the pig at a faster rate than a still air environment by the method of convection. Many pigs have been lost through heat stress by increasing air speed when the air temperature reaches or exceeds the core temperature of the pig because it effectively makes the environment hotter. Figure 1 is an example EET that relates pig size and environment (air speed) at an actual air temperature of 41°F. As might be expected, younger pigs are more susceptible to higher air speeds than mature pigs. Intuitively this makes sense, but how can this be explained from an energy exchange point of view? Remember, the thermal comfort of a pig is a direct result of energy exchange with its environment, so this result should be able to be explained from a heat transfer point of view. Air temperature and air flow directly affect convection heat transfer. Also, the pig’s surface area exposure to an environment directly affects convection heat transfer. For young pigs, the surface area to weight ratio is higher compared to mature pigs. Therefore, for any given combination of air temperature and air flow, a young pig, per pound of body weight, will transfer more heat to or from its surroundings implying that the effect of air flow is greater for younger pigs.

有效环境温度很方便，也很容易理解。计算有效环境温度的具体方法非常复杂，这里不再展开，但这个概念却很重要。最重要的是要牢记热环境以热的形式带走（或给予）能量给猪的难易程度直接影响到猪的舒适程度以及生产量。当气温低于猪的体内温度时，热的，空气流速慢的环境与热的，空气流速快的环境相比，前者的EET值更高。而当气温高于猪的体内温度时，空气流速慢的猪舍的有效环境温度值要低。为什么呢？因为气温高于猪体内温度时，快速流动的空气通过对流会以更快的速度转移给猪更多的热量。当周围气温达到或超过猪体内温度时，若增大空气流速，就会产生热压力，使环境温度升高，会伤害到猪。图1即是在41°F时有效环境与猪大小及环境（空气流速）的关系。可以想到，仔猪更易受流速快的空气的影响。凭直觉人们可以得出此结论，但怎样从能量交换的角度解释这一现象呢？记住，猪与其周围环境的能量交换直接导致了猪在热量上的舒适度。由此，我们一定能从热量交换的角度解释这一现象。气温和空气流速直接影响对流热转移。而且，猪体表暴露于环境的面积大小也直接影响对流热转移。仔猪的体表面积与体重比要大于成猪。因此，给出任意气温和风速，仔猪每磅会从环境中转移走（或获取）更多的热量，这意味着空气流速对仔猪的影响更大。

图1，气温41华氏度下有效环境温度和风速对猪的影响

The EET chart given, developed for the combined influences of air temperature and flow, also highlights two other important facts regarding a pig’s energy exchange. First, as indicated with this chart, the influence of air flow on the pig’s thermal environment decreases with increasing air speed. This occurs because of a boundary layer of air that exists on the pig’s surface. This boundary layer of air acts like a blanket of insulation. This boundary layer decreases with increasing air speed, but can only be decreased to a given minimum. Therefore, at some air speed level and beyond, the convection heat transfer to the surrounding air reaches a maximum. This maximum occurs at about 3.5 miles per hour, and this is the reason why tunnel ventilated barns are designed for a maximum air speed of about 3.5 miles per hour. Beyond this level, we have reached a point of diminishing returns via convection.

Second, as air temperature increases, the influence of higher air speeds decreases. In fact, if the air temperature is exactly equal to the pig’s surface temperature, no heat can be transferred by convection methods, regardless of air flow. Without a difference in air temperature, no heat can be transferred via convection. This example is shown in Figure 2, where pigs are exposed to a 95°F air temperature.

图2，气温为95华氏度下有效环境温度和风速对猪的影响

图1给出的有效环境温度表，主要数值由气温和气流组成，强调了猪能量转换的另外两个重要因素。首先，如图所示，随着风速的增大，气流对于猪热环境的影响会减小。之所以出现这种状况，是因为猪体表存在一种界层。这种界层好像起隔离作用的保护毯。随着空气流速的增大，界层会减少（界层的保护作用会降低），但也只会降低到某个最小值。因此，在一定的风速或在大于此特定风速，猪与环境间的热转移量会达到最大值。一般风速达到每时3.5英里时，对流热转移量最大。人们设计出隧道式通风的猪舍，即是力求将风速达到3.5mph,超过这个风速值，通过对流转移的热量会减少。其次，随着气温升高，高流速空气对猪的影响会减小。事实上，如果气温近同于猪的体表温度时，不管空气流速是多少，用热转移的方法几乎无法转移热量。若没有温度差，通过对流就无法转移热量。参见图2，95°F 气温下猪的状况。

The pig’s response to its thermal environment and the resulting EET play a big role in how best to control an optimum thermal environment. For example, young pigs, because of their susceptibility to high air flow, need ventilation systems and environmental control strategies that reduce any potential drafting air flows. With more mature pigs, less attention is needed to this detail. Also, it is important that a control system recognizes when it might be dangerous to artificially increase air flow during extremely hot conditions. As Figure 3 shows, high air speed combined with extreme air temperature actually hastens heat stress, unless some form of evaporative cooling is present.

猪对热环境的反应以及有效环境温度对于掌控最佳热环境有重要的作用。例如，仔猪对高空气流速具有易感性，需要我们利用通风系统及环境控制策略来减少任何潜在的较快空

气流动。成猪越多，对通风系统及控制策略的要求就越少。并且，在极热的环境下，人为增大空气流速可能是有害的，而控制系统能否识别这点是非常重要的。如图3所示，在极高的气温下，高流速空气实际上加强了热压力，除非我们用一些蒸发转移热的形式给猪降温。

图3，气温104华氏度时有效环境对成猪的影响

Defining Cold and Heat Stress冷应激和热应激的定义

The lower critical temperature (LCT) is generaly accepted as the effective temperature of the thermal environment where pigs will need to consume more feed and apply extraordinary measures to keep warm. Likewise, a pig's upper critical temperature (UCT) is generally accepted as the effective temperature of the thermal environment where pigs suppress feed intake and apply extraordinary measures to keep cool. Between the LCT and UCT, there is an optimum thermal environment region, depending on pig age, where pigs will perform best. Our goal in any environmental control method is to achieve this region of effective environmental temperature that optimizes production efficiency. The LCT and UCT are both functions of pig age as Figure 4 indicates.

较低临界温度（LCT）lower critical tempreture指猪需要增大采食量并采取特别的方式才能保持温暖的热环境有效温度。

较高临界温度（UCT）upper critical tempreture指猪通过减少进食量，并采取特别的方式保持体内凉爽的热环境有效温度。在较低临界温度和较高临界温度之间，依据猪龄，是最佳热环境温度区间。在最佳热环境温度中，猪的状况最佳。我们使用环境控制方法的目的就是想使温度处于这种有效环境温度区间内，使生产效率最优化。LCT与UCT都与猪龄有关，见图4.

图4，猪舒适温度

The optimum temperature range is the band of EET that a control system should be designed to achieve. EET levels outside this band of temperatures diminish production efficiency.

要达到最佳温度区间即有效环境温度区间，需要设计控制系统。在此温度区间外的有效环境温度值会降低生产效率。

Recognizing and Controlling Cold Stress冷应激的识别及控制

Behavioral responses by the pig can be an indicator of cold stress. Pigs huddling is a sure indication that they are feeling cold as a result of air temperature, air flow, flooring temperature, surrounding wall temperature, or a combination of any of these factors. A simple strategy for controlling cold stress is simply to raise the air temperature in the barn. However, this can be an expensive option. A better approach would be to assess the environment to determine the cause of cold stress. An assessment of air flow may indicate elevated levels, and an adjustment of the inlet air direction may be all that is needed to control cold stress.

猪的行为可以体现其冷应激状况。当猪挤作一团时，明显是因为寒冷。它们感到寒冷的原因有很多，如气温，气流，地表温度，四周墙体温度或其中某几个因素的共同作用。控制冷压力的简易方法是提高猪舍气温，但成本可能会高。更好的方法是评估环境确定受冷成因。对空气流速的评估可能能帮助我们判断出空气流速是否较快，或者也许仅需调整下入口空气气流流向就能解决猪的受冷问题。

Recognizing and Controlling Heat Stress热应激的识别及控制

Like cold stress, behavioral responses by the pig can be a good indicator of heat stress. For example, heavy breathing or panting is a clear indication that pigs are attempting to lose more heat to their surroundings via evaporation methods, and this is a clear behavioral response to heat stress. Pigs suppress eating and increase water intake during periods of heat stress. Also, lying patterns become very spread as pigs attempt to increase their surface area to the surroundings. All these responses are clear indicators that the pig is heat stressed. Controlling heat stress can be accomplished with two major methods: direct and indirect cooling. Direct cooling is any method that directly contributes to the increase in heat transferred to the surrounding area. An obvious example of this would be to sprinkle the pig’s body with water and allow energy from the pig to supply the needed latent heat of vaporization to evaporate this water. This direct cooling method can be further increased by increasing the air speed over the wetted surface of the pig. In contrast to this, indirect cooling would involve cooling the air surrounding the pig and relying on convection to increase the heat transferred to the surrounding area. As a general rule, direct cooling is much more efficient in removing excess heat from the pig, and should be the first line of defense against heat stress.

同冷应激一样，猪的行为也可以很好的显现出其受热状况。例如出现呼吸粗重，气喘现象明显说明猪在试图通过蒸发方式将自身热量转移给周围环境，这是对其所受热压力的行为上的反映。受热时，猪会减少进食量，增大饮水量，四肢伸展躺于地面来增大体表与地面的接触面积。控制热压力主要有两种方法：直接降温和间接降温。直接降温指任何可以直接增加向周围环境转移热量的方法。最明显的例子是给猪冲水，让猪将能量提供给所需的潜性热蒸发来蒸发掉这些水。这种直接降温方法还可以通过加快猪打湿部分周围空气流速的方式来完成，效果更佳。相反，间接降温包括降低猪周边空气温度，依靠对流增大向环境中转移的热量。一般，直接降温可以使猪更有效地转移多余热量，因此，在应对热压力时，应首先考虑。

In extreme heat stress conditions, increasing the air speed over the pig without the addition of liquid water for evaporation can actually be detrimental. Figure 3 outlined this case for 220 lb. pigs. If the air temperature is 104°F, which is slightly above the 103.5°F core temperature of the pig increasing the air speed actually increases the EET since now the effect of increased air speed is to convectively add heat to the pig at increasing rates.

在极热的环境下，不用液态水来蒸发，而仅用加大空气流速的方法来降温在实际上可能是有害的。图3显示了这种情况下220磅的猪的状况。猪的体内温度大约是103.5°F, 假如气温为104°F, 此时加快空气流速实际上是增大了有效环境温度值。因为此时加快空气流速只是在以更快的速度通过对流转移给猪更多的热量。

The Economics of Optimal Thermal Environments最佳热环境的经济学意义

表1，气温对猪采食量的影响

表头从左到右：低于最佳热温度的华氏度数，额外食物磅/猪/天；1000载量的猪舍，磅/天/舍; 额外饲料的费用花费/天/舍。

No one should implement sophisticated environmental controls or housing systems unless evidence exists that there is a benefit. A benefit might be decreased labor expense, a decrease in disease outbreaks, an increase in profitability, an increase in worker job satisfaction, or any number of reasons that the producer feels is a benefit to the operation. Evidence does exist that there is a clear economic benefit for maintaining an optimal thermal environment for the pig.

For example, studies have shown that for every degree Fahrenheit below the optimum temperature, pigs less than about 60 lb. need to consume 0.015 lb./day more feed and pigs greater than about 80 lb. need to consume 0.044 lb./day more feed to supply the extra energy that is being lost to the pig’s surroundings. Table 1 gives a more complete picture of this trend for a 1000 head facility housing 40lb. pigs. For the example case given in Table 1 for 40 lb. pigs, the criteria for achieving the degrees of coldness listed can be met in several ways. In a well-insulated barn with low air speeds at pig level, maintaining the barn at 5°F, 10°F, or 15°F below the optimum temperature of 69°F will achieve the degrees of coldness listed. Likewise, using the concept of effective environmental temperature, this same degree of coldness could be achieved in a well-insulated barn, maintained at 69°F, with pig-level air speeds of 0.8 mph, 2.0 mph, and 4.5 mph, respectively (see Figure 5). The condition of 15°F coldness seems to be very severe, and one would think never attainable in a barn unless a ventilation control problem exists, thus forcing the actual air temperature to this level. However, when viewing this issue from an effective environmental temperature viewpoint, a well-insulated barn with a drafty environment can easily attain these levels of coldness.

若没有证据证明评估热环境会带来益处，就不会有人采取复杂的环境控制措施或者猪舍环境系统。好处可能是工人开支额的减少，疫病爆发次数的减少，收益的增加，工人工作满意度的提升，或是任何养殖人员认为的评估热环境带来的益处。确有证据证明维持猪的热环境会带来明显的经济效益。

例如，研究表明，对于体重低于60磅的猪，体温每低于最佳温度值一个华氏度，每天就要多消耗0.015磅的食物，体重大于80磅的猪，每天要多消耗0.044磅的食物用来补充因应付冷环境而消耗掉的能量。表1以一家可装1000头40磅猪的猪场为例给出了此理论的具

体图景。表1给出了一些冷温度的标准数值，可采用一些方法使气温分别达到这些数值，以方便实验。我们已知道，最佳温度为69°F,若将一个隔离良好且空气流速慢的猪舍温度分别保持为低于最佳温度5°F,10°F,15°F，所得气温值即是表格中列出的受冷程度。同样，用有效环境温度的概念，令隔离良好，气温达到最佳温度的猪舍将气温也同样分别调为低于最佳温度5°F,10°F,15°F, 同时将空气流速设为0.8英里每时，2英里每时，4.5英里每时（见图5）。我们可知，冷程度为低于最佳温度15°F的时候，猪的状况最糟糕。人们会认为此温度难以达到，除非猪场的通风控制上存在问题，才能迫使实际气温到达这种程度。但从有效环境温度的角度看，一个隔离良好同时具有通风环境的猪舍会很容易达到这样的冷程度。

图5，69华氏度时有效环境温度对40磅重猪的影响

Environmental Control Methods环境控制方法

Many different designs exist today to modify the pig’s thermal environment. A wide variety of controlsystems, ventilation arrangements, and building designs exist from which to choose the best system for a given situation. There are no hard and fast rules for making these decisions, but a few guiding principles should be kept in mind.

The climate. Building design is most often the result of climate and pig maturity level. For example, a naturally ventilated (NV) barn for finishing pigs in North Carolina would be doomed to failure because in the heat of the summer, as much as 14% of the time the wind is calm. Since the primary hot weather ventilation force for NV barns is wind, at least 14\% of the time the barn would be grossly under-ventilated causing severe heat stress conditions. Likewise, a tunnel ventilated (TV) barn for finishing pigs in Iowa is needed very few times during the year because during the heat of the summer, it is calm less than 2 percent of the time. Much of the summer can be very nicely ventilated with pure NV methods. The environmental control system should be intelligent enough to make a decision between transition from/to NV or TV.

The desire. What is your objective as a producer? If your objective is to create a tightly controlled environment prepared for any climate, then a sophisticated ventilation design and control system is required. If you are trying to simply keep animals from the severest climates, then a partially

enclosed building with no active ventilation or control system is adequate.

现今有多种不同的设计方法来改变猪的热环境。我们可以依具体情况来从宽松多样的控制系统，通风措施以及建筑设计方法中选择一个最佳系统。做这样的选择没有什么固定不变的规则，但应参考一些指导性的原则。比如

1.气候因素猪场设计通常受气候及猪成熟度的影响。例如，加利福尼亚州用自然

通风（NV）的猪场要养成猪注定是要失败的，因为在炎热的夏天，14%的时间

都是无风的。而在炎热的天气里，一个自然通风的猪舍最主要的通风力就是风，

14%的时间里猪舍都得不到通风的话，会导致严重的热压力。同样，爱荷华州的

隧道式（TV）猪场养成猪只需花费很少的时间。因为在炎热的夏季，不到2%的

时间没有风。夏季的大部分时间用自然通风的方法就可以非常好的进行猪舍通

风。因此，NV和TV方式间的转换要做灵活选择。

2.欲望作为一名养殖人员，你的目标是什么？如果你的目标是创造可以适应各种

气候的设计完善的环境控制系统，那么就需要一个复杂的通风设计和控制系统。

如果你只是想使猪远离严酷气候的伤害，那么一个部分封闭，有良好通风或控制

系统的猪舍就足够了。

The classification on control usually falls under one of the following groups: cold, modified, or controlled environments. No attempt is made with cold facilities to control the ventilation process with most of the building open to the outdoors. For these facilities, typical of modified open-front buildings, almost no attempt is made to reach optimum growing conditions. A modified building usually has some insulation, manually controlled curtains and/or ridge vents, and a heating system to keep any water lines from freezing. The objective with this design is to maintain the inside temperature slightly above outside with swings in temperature following the outdoor temperature. In a controlled building, a great deal of attention is given to controlling the environment to remove unwanted variations. With these designs, usually the latest and most sophisticated ventilation and control strategies are incorporated, with various ventilation strategies in one building to respond to varying climates by season.

依对环境控制能力大小对建筑的划分有3类：被动的，改进的和良好的环境控制建筑。被动的环境控制建筑不做任何的措施操控通风过程，大多数建筑都对户外敞开。这些猪场基本由前部开放的建筑改建而来，基本不会创造条件使猪达到最佳生长环境。改进的环境控制建筑通常有一些隔离措施，比如安装手控窗帘，在屋脊上设立通风口，以及提供供暖系统来防止水结冰等。这种设计的目标是保持室内温度略高于室外温度，并随室外温度的变化而改变。而环境控制良好的建筑会将大部分注意力放在环境控制上，并移除那些有害因素。在这些环境控制良好的建筑设计中，融汇了最新和最复杂的通风和控制方法，使一个建筑可以用多种通风策略来应付四季气候的变化。

Summary总结

Depending on your desire as a producer, several options exist for maintaining a thermal environment at levels you desire. Pigs surely will adapt to the environment, but many times it is at a cost. This cost might be in the form of extra feed intake during periods of cold stress, or suppressed feed intake and growth during periods of heat stress. Evaluating the environment at

regular intervals and assuring maintenance of the environment within an optimum range of effective environmental temperatures will efficiently house pigs and most likely reduce the susceptibility from thermally induced stressors.

作为一个养殖人员，你可以依据你的需求来选择保持热环境的方法。猪自身当然会适应环境，但很多时候这种本能的适应要付出一定的代价，可能是在受冷时吃掉额外的食物，也可能是在受热时减少进食量，放慢生长速度。时不时地评估下环境，确保环境温度保持在有效环境温度的最佳区间内，会更有效地饲养猪，最大限度地减少热量引发的压力，可以减小猪对环境的易感性。

A wide variety of technologies exist to help assess the thermal environment. Hand-held instruments and periodic observations of pig behavior can be used to evaluate the thermal environment and provide the producer with feedback for making any required changes to the environment. Sophisticated control systems exist to provide continuous monitoring of the thermal environment and necessary control modifications to the barn in an attempt to achieve the optimum thermal conditions for pork production. This level of sophistication now allows for barns to be controlled not only for air temperature, but also for humidity and air flow levels in an attempt to assess and control the effective environment of the pig. In today's pig production industry, a mistake in thermal environmental control can be costly, as small, added costs of production are multiplied through many similar barns and pigs.

多种科学技术可以帮助我们评估热环境，手提设备及周期性的观察猪的行为也可用来评估热环境，为养殖人员提供反馈，使他们根据需要对环境做出调整。先进的控制系统可以长久地监测热环境，并适时作出必要的改变，使猪舍达到最佳热状态。环境控制的复杂性不仅需要猪舍控制气温，还需要控制湿度，空气流速，只有全面考虑到这些因素，才能评估，控制猪的有效环境。在当今的猪养殖工业中，对热环境控制的小小的错误的评估可能会造成重大损失，一个猪场在生产上多出的少部分花费并不明显，但成千上万个猪场和猪因多余的花销而带来的损失可能会是惊人的。