Pigs are much more sensitive to heat than other animals so during periods of hot weather it is important to look at ways to reduce heat stress.

豬相比于其他動(dòng)物對(duì)熱更為敏感，高溫季節(jié)，想方設(shè)法降低豬熱應(yīng)激的發(fā)生至關(guān)重要。

Why are pigs so sensitive to heat stress?

為什么豬容易發(fā)生熱應(yīng)激?

Most animals can transfer internal heat to the outside of the body by sweating and panting – these are the two most important tools for the maintenance of body temperature and form their inbuilt evaporative cooling system.

多數(shù)動(dòng)物可將體內(nèi)熱量通過(guò)汗液和呼吸排出體外，這是動(dòng)物維持體溫恒定和保持自身調(diào)節(jié)能力的兩種重要方式。

However, pigs do not sweat and have relatively small lungs. Due to these physiological limitations and their relatively thick subcutaneous fat, pigs are prone to heat stress. The two obvious symptoms observed when pigs are exposed to heat stress are increased respiration rate and loss of appetite. The latter reduces internal heat production.

然而，豬不出汗，肺也相對(duì)較小。這些生理上的局限，再加上豬皮下脂肪較厚，使豬易于發(fā)生熱應(yīng)激。當(dāng)豬出現(xiàn)呼吸速率加快和食欲不振這兩個(gè)明顯的臨床癥狀時(shí)，往往提示豬發(fā)生熱應(yīng)激，隨后其機(jī)體產(chǎn)熱相應(yīng)減少。

If heat stress continues, pigs start to drink excessive amounts of water (increasing loss of electrolyte) and accumulate acids produced within the body (causing a loss of acid/base balance). This may eventually result in diarrhoea or death in severe cases.

持續(xù)的熱應(yīng)激使豬開始過(guò)量飲水(引起電解質(zhì)流失)，體內(nèi)酸不斷累積(破壞體內(nèi)酸堿平衡)，從而導(dǎo)致豬發(fā)生腹瀉，嚴(yán)重時(shí)甚至引發(fā)死亡。

What does current research say about heat stress?

目前的研究對(duì)熱應(yīng)激怎么看?

A recent publication by Pearce et al. examined what happened to the intestinal structure when pigs were exposed to heat stress. The research showed that exposure to 35°C for 24 hours significantly damaged the intestinal defence function and also increased plasma endotoxin levels. The authors explained that when pigs are exposed to heat stress (even for as little as two to six hours) their intestinal defence systems are significantly compromised and this provides opportunity for infection as pathogenic bacteria can invade the body more easily. Therefore, heat stress can create secondary infection if sanitary conditions are poor.

Pearce等人研究了豬發(fā)生熱應(yīng)激時(shí)其腸道結(jié)構(gòu)的變化，結(jié)果表明，豬在35°C環(huán)境下持續(xù)24小時(shí)會(huì)明顯損傷其腸道防御功能，還會(huì)引起血漿內(nèi)毒素水平升高。該研究顯示，當(dāng)豬發(fā)生應(yīng)激時(shí)(即使只有2小時(shí)～6小時(shí))，其腸道防御系統(tǒng)會(huì)大大受損，病原菌很容易侵入體內(nèi)使感染率大大提高。如果環(huán)境衛(wèi)生狀況不佳，熱應(yīng)激還會(huì)引起繼發(fā)感染。

Consequences of heat stress on the performance of pigs

熱應(yīng)激對(duì)豬生產(chǎn)性能的影響

Bigger pigs are more prone to heat stress and the reduction in growth performance is greater than for smaller pigs.

Figure 1 shows the magnitude of performance loss in 25, 50 and 75kg pigs when ambient temperature was increased from 14°C to 35°C. Average daily gain (ADG) starts decreasing when 75kg pigs were exposed to temperatures above 23°C, while for 25-kg pigs, ADG starts to decrease when exposed to temperatures above 27°C.

Figure 2 shows critical temperatures at various body weights - this information can be used as an index for the temperature management of different sheds housing varying age groups of pigs.

大豬比小豬更容易發(fā)生熱應(yīng)激，且熱應(yīng)激時(shí)生長(zhǎng)性能比小豬下降得更明顯。

圖1顯示了當(dāng)溫度從14°C升高到35°C時(shí)，體重分別為25kg、50kg和75kg豬生產(chǎn)性能的下降程度。重75kg的豬在溫度超過(guò)23°C時(shí)，日增重開始降低;而重25kg的豬在溫度超過(guò)27°C時(shí)，日增重才開始降低。

圖2為不同體重豬生長(zhǎng)發(fā)育的臨界溫度，可為控制各飼養(yǎng)階段豬的環(huán)境溫度提供參考。

Figure 1. Effect of ambient temperature on the average daily gain of grower-finisher pigs

圖1 溫度對(duì)生長(zhǎng)肥育豬日增重的影響

(圖中英文翻譯，參照翻譯修改圖片)ADG：平均日增重，g/天，Ambient temperature: 環(huán)境溫度，°C  體重75kg，體重50kg，體重25kg

Figure 2 Pig bodyweight has a significant effect on the critical temperature for average daily feed intake (ADFI) and average daily gain (ADG)

圖2 豬體重對(duì)豬日采食量和日增重的臨界溫度有顯著影響

（ADG：日增重 ADFI：日采食量）

At what temperature and humidity do pigs get heat stressed?

豬在怎樣的溫濕度環(huán)境下會(huì)發(fā)生熱應(yīng)激?

pigs generally develop heat stress at much lower temperatures when the humidity is high. Iowa State University recently released a heat stress index chart (Figure 3) which can be used as a decision tool for implementation of management strategies to reduce heat stress.

溫度和濕度對(duì)熱應(yīng)激的發(fā)生影響很大。通常，豬在高濕環(huán)境中即使溫度較低也會(huì)發(fā)生熱應(yīng)激。美國(guó)愛荷華州立大學(xué)近期發(fā)布了濕熱應(yīng)激指數(shù)圖(圖3)，可為制定減輕熱應(yīng)激的措施提供參考依據(jù)。

The chart shows that an average humidity of 40 percent coupled with temperatures higher than 28°C will significantly affect intestinal health and performance of grower-finisher pigs. The temperature tolerance is lower for breeding herds.

圖3顯示，濕度40%、溫度超過(guò)28°C時(shí)，生長(zhǎng)肥育豬的生長(zhǎng)性能和腸道健康會(huì)受到顯著影響。種豬對(duì)溫度的耐受度較低。

Figure 3 Heat Stress Index for grow-finish swine

圖3生長(zhǎng)育肥豬濕熱應(yīng)激指數(shù)圖

Room temp:環(huán)境溫度 Relative humidity 相對(duì)濕度 No heat stress 無(wú)熱應(yīng)激區(qū) Heat stress alert警戒區(qū) Heat stress danger危險(xiǎn)區(qū) Heat stress emergency緊急區(qū)

Recommended management tools to reduce heat stress

減輕熱應(yīng)激的管理方法

· Increase ventilation and airflow and regularly check cooling system is in good working order, e.g. spray cooling.

· Reduce stocking density if possible.

· Maintain drinking water temperature as low as possible - around 10°C is ideal but difficult to achieve.

· Avoid feeding between 10.00am and 4.00pm - the hottest period of the day.

· Supplement electrolytes and antioxidants through the water supply.

· Increase dietary energy density.

· Minimise excess non-essential amino acids and fibre (minimising intestinal fermentation and therefore heat production).

· Increase availability of antioxidants through the diet such as vitamin E and betaine.

· 加強(qiáng)通風(fēng)和空氣流動(dòng)，定期檢查降溫系統(tǒng)是否正常運(yùn)作，如噴霧冷卻;

· 若條件允許，減少飼養(yǎng)密度;

· 盡量降低飲用水溫度，理想溫度約10°C，但很難達(dá)到;

· 避免在每日高溫時(shí)間(上午10點(diǎn)～下午4點(diǎn))喂食;

· 通過(guò)飲水補(bǔ)充電解質(zhì)和抗氧化劑;

· 增加能量供給;

· 減少多余非必需氨基酸和纖維的攝入(減少腸道發(fā)酵從而減少機(jī)體產(chǎn)熱);

· 通過(guò)添加VE和甜菜堿等營(yíng)養(yǎng)素使抗氧化劑有效發(fā)揮作用。