刁华杰 冯京海 刁新平
(1.中国农业科学院北京畜牧兽医研究所,北京100193;2.东北农业大学动物科技学院,哈尔滨150030)
环境高温对蛋鸡生产性能的影响及营养调控措施
刁华杰1,2冯京海1*刁新平2
(1.中国农业科学院北京畜牧兽医研究所,北京100193;2.东北农业大学动物科技学院,哈尔滨150030)
夏季高温是影响蛋鸡生产性能的一个重要因素。近年来随着风机+湿帘等降温设施的普及,夏季规模化蛋鸡舍内的温度一般可以控制在30 ℃以下,因此在实际生产中往往忽略夏季高温的不利影响。本文针对环境高温尤其是循环高温对蛋鸡生产性能的影响进行总结归纳,以期引起生产以及研究人员对于夏季高温的重视,并从饲粮能量和粗蛋白质水平方面总结缓解高温应激影响的营养调控技术,旨在为高温季节蛋鸡合理配制饲粮及饲养管理提供科学依据。
高温;蛋鸡;生产性能;营养调控
环境高温是影响蛋禽生产的一个重要因素[1-2]。高温可引起蛋禽产蛋性能和蛋壳品质的下降,造成巨大的经济损失[3-4],据估算美国养殖业每年因高温造成的经济损失高达16.9亿~23.6亿美元[5]。我国禽蛋产量巨大[6-7],据《中国统计年鉴(2015)》统计,2014年我国禽蛋产量达到2 893.9万t,但其中禽蛋产量较高的地区主要集中于华中、华东等地区,而这些地区夏季日平均气温普遍高于25 ℃。目前我国规模化蛋鸡场湿帘+风机等降温设施基本普及,通过湿帘的蒸发作用,夏季家禽舍内温度最高可以降低10~12 ℃,一般可以控制在30 ℃以下[8],因此实际生产中往往忽略夏季高温的影响。然而湿帘通风的降温效果受环境湿度的影响[9],并且舍内纵向距离以及垂直高度温差较大[8]。夏季部分时间内,蛋鸡舍内部分区域的温度仍可超过32 ℃[10-12]。本文针对环境高温尤其是循环高温影响蛋鸡生产性能的研究进行总结归纳,以期引起生产以及研究人员对于夏季高温的重视。并从饲粮能量和粗蛋白质水平方面总结缓解高温应激影响的营养调控技术,旨在为高温季节蛋鸡合理配制饲粮及饲养管理提供科学依据。
1.1 采食量
当环境温度过高时,家禽通过降低采食量,减少产热量以维持体温恒定[13]。环境高温一方面可能直接抑制家禽下丘脑的嗜食中枢,引起食欲减退[14];另一方面可能由于肠道蠕动减慢[15],饮水量增加[16-17],导致消化道充盈,负反馈的抑制嗜食中枢[18],导致采食量下降。
大量文献报道环境高温降低蛋鸡的采食量,其中主要为持续高温的研究结果。与适温21~22 ℃相比,25~28 ℃的持续高温对蛋鸡采食量影响较小[19-21];30~32 ℃的持续高温导致蛋鸡采食量降低19.7%~26.3%[14,20-25];33~35 ℃的持续高温导致蛋鸡采食量降低22%~52%[21,26-29]。实际生产中并不存在长时间的持续高温,而符合夏季生产实际的循环高温的研究较少。Emery等[30]报道,在21.1~37.7 ℃循环高温下,蛋鸡采食量平均下降15.6%。Miller等[31]发现27~38 ℃循环高温使得蛋鸡采食量显著降低34.8%。Mashaly等[29]发现23.9~35.0 ℃循环高温第1周蛋鸡采食量降低33.3%,而第5周仅降低14.9%,表明随着热应激时间的延长,蛋鸡对于循环高温逐渐适应。
De Andrade等[22]对比了循环高温和持续高温的影响,发现26.7~35.6 ℃循环高温下蛋鸡采食量降低22.1%,而31 ℃持续高温使蛋鸡采食量降低了26.3%,持续高温的影响显著高于循环高温;Mashaly等[29]也有相似发现。以上研究结果表明,即使每天鸡舍内温度短时间内达到35.6~37.7 ℃的高温,蛋鸡采食量下降程度低于或与30~32 ℃的持续高温下相似。而在夏季实际生产中不存在长时间的持续高温,因此持续高温的研究结果并不能很好地指导生产实践。另外随着湿帘+风机降温设施的普及,蛋鸡舍内温度一般低于30 ℃,因此需要进一步研究较低循环温度对蛋鸡采食量的影响。
1.2 产蛋性能
当环境温度过高时,蛋鸡采食量下降,同时家禽的消化代谢也受到影响[32-33],进而导致营养物质摄入不足,引起产蛋性能的下降。另外环境高温可能直接影响蛋鸡卵泡的发育[34-35],也可能是引起产蛋性能降低的原因之一。
有关环境高温影响蛋鸡产蛋性能的研究一般采用持续高温模型。与常温21~23 ℃相比,25~28 ℃的持续高温对蛋鸡产蛋率、蛋重和体重的影响较小[19-20];30~32 ℃持续高温使得产蛋率降低3.4%~19.6%[22-25]或对产蛋率无显著影响[19-21,23],蛋重下降0.6%~5.9%[19,20,24-25],体重降低9.2%[19];33~35 ℃持续高温使得产蛋率降低16.60%~28.82%,蛋重下降3.7%~9.9%[21,26-28,36],同时体重降低了11.9%[21]。
有关循环高温的研究相对较少,Emery等[30]研究发现,21.1~37.7 ℃循环高温下蛋鸡产蛋率变化不显著,蛋重显著降低7.4%,同时蛋鸡体重降低。De Andrade等[22]同样发现,循环高温26.7~35.6 ℃下蛋鸡产蛋率降低不显著,蛋重和体重显著降低;其他研究也有相似发现[29,31]。上述研究结果表明,循环高温下,即使舍内温度短时间内达到35.6~37.7 ℃的高温,对蛋鸡产蛋率的影响并不显著,仅显著降低蛋重和蛋鸡体重。这可能由于循环高温下蛋鸡采食量降低较小,而蛋鸡首先维持繁殖机能的需要,在采食量降低,营养摄入减少的条件下,通过消耗体内能量和蛋白质的储存维持产蛋,因此产蛋率降低不显著,但蛋重和体重下降。
1.3 蛋壳品质
环境高温影响蛋壳品质,导致鸡蛋破损率增加,这可能是夏季高温影响蛋鸡生产经济效益的重要因素之一。研究发现,暴露在30~32 ℃持续高温下,蛋壳厚度降低2.9%~5.5%[29,37],蛋壳重降低7.2%[38],蛋壳破损率显著提高到5.3%[22];暴露在33~35 ℃持续高温下,蛋壳厚度降低7.8~8.5%[28,39],蛋壳重降低13.5%~20.0%[28,38],蛋壳破损率高达13%[39]。环境高温影响钙、磷的吸收和利用[40-41],也可能直接影响蛋壳腺的收缩[42],导致蛋壳品质下降。
循环高温对蛋壳品质的影响研究较少。Emery等[30]研究发现,21.1~37.7 ℃循环高温使得蛋壳厚度降低15.4%;De Andrade等[22]发现26.7~35.6 ℃循环变温使得蛋壳厚度降低8.5%;Mashaly等[29]也有类似报道,表明较高循环温度(21~37 ℃)显著影响蛋壳品质,较低循环温度(30 ℃以下)是否影响蛋壳品质还需进一步研究。
高温环境下蛋鸡采食量下降,营养物质消化率降低,导致营养物质和能量摄入不足,这可能是高温降低蛋鸡生产性能的主要原因。Jackson[43]发现,和自由采食相比,蛋鸡限饲常规饲粮后产蛋性能显著降低,但限饲相同数量的高营养饲粮产蛋性能不变。由此推测,提高蛋鸡饲粮的营养水平可以缓解环境高温的不利影响,为此研究人员开展了一系列的研究。
2.1 提高饲粮能量水平
高温环境下将饲粮代谢能(ME)由13.35 MJ/kg提高到14.78 MJ/kg可显著提高肉鸡的日增重,降低料重比[44]。但饲粮ME提高627.9 kJ/kg对肉鸡增重无显著影响[45],推测肉鸡饲粮ME提高值较小时,并不能显著改善肉鸡能量的摄入,因此不能缓解高温对肉鸡生产性能的不利影响。有研究表明高温下添加脂肪可显著提高肉鸡增重[44],这可能是由于脂肪的热增耗低,饲粮中使用脂肪替代部分碳水化合物可以显著提高肉鸡ME的摄入量。
高温环境下提高蛋鸡饲粮ME的研究较少。Marsden等[20]在不同环境温度下(15~30 ℃)给蛋鸡饲喂3种能量水平(10.88、11.92和12.97 MJ/kg)的饲粮,发现提高饲粮能量水平能提高蛋鸡的产蛋率和蛋重。Peguri等[19]提高饲粮能量水平可以显著增加蛋重,但当环境温度超过26.7 ℃时提高能量水平对蛋重的影响消除,这可能是由于高温环境下提高饲粮能量水平,由于采食量的降低,能量的摄入量增加并不显著。而Usayran等[46]分别在常温和高温环境下研究添加脂肪(保持饲粮能量和粗蛋白质水平不变)对蛋鸡的影响,发现添加脂肪能显著提高产蛋高峰前期蛋鸡的增重、蛋重和产蛋量,推测可能由于添加脂肪增加能量的摄入量所致。
2.2 调整饲粮粗蛋白质和氨基酸水平
关于高温环境下家禽饲粮粗蛋白质水平有2种不同观点。一种是饲喂高蛋白质水平饲粮,以缓解采食量下降导致的粗蛋白质摄入量不足,另一种是饲喂低蛋白质水平饲粮并补充必需氨基酸。在肉鸡中研究发现,高温环境下饲喂高蛋白质水平饲粮可显著提高增重和饲料效率[47-48],但另有研究发现提高饲粮粗蛋白质水平对肉鸡生长无显著影响[49-50],甚至有不利影响[51]。蛋白质的热增耗较高[52],这可能是高温环境下饲喂高蛋白质水平饲粮的弊端。选择性偏好试验也表明高温环境下肉鸡不喜欢高蛋白质水平饲粮[53]。因此可能在极端高温[54]或并发疾病[55]条件下饲喂高蛋白质水平饲粮有益,但一定要选择高品质蛋白质原料,低消化率的蛋白质可能会加重家禽的热应激反应[33]。Cheng等[51]发现,高温环境下饲喂16%或18%粗蛋白质水平饲粮并补充5种必需氨基酸与20%粗蛋白质水平饲粮相比肉鸡增重无显著差异。Alleman等[56]发现32 ℃高温环境下,即使补充5种必需氨基酸,16%粗蛋白质水平组增重及饲料利用效率仍低于20%粗蛋白质水平组,表明高温环境下低蛋白质补充氨基酸饲粮并不能改善肉鸡的生长状况。
高温环境下蛋鸡饲粮适宜粗蛋白质水平的研究较少。研究表明高温环境下饲喂低蛋白质补充氨基酸的饲粮会导致蛋重下降[57]。Torki等[58]研究了夏季高温环境下不同粗蛋白质水平(10.5%、12.0%、13.5%、15.0%和16.5%)饲粮对蛋鸡的影响,赖氨酸、蛋氨酸等必需氨基酸水平相同,通过二次曲线模型分析得出,维持产蛋量不显著降低的粗蛋白质需要量为14.62%,表明高温环境下在满足必需氨基酸需要量时可适当降低饲粮粗蛋白质水平。Reid等[59]分别在21和35 ℃下饲喂不同粗蛋白质水平的饲粮,使2个温度下粗蛋白质的摄入量相同(12.7~20.5 g/d),ME平均摄入量为937.6(高温)和1 460.9 kJ/d(适温)。在21 ℃时增加粗蛋白质摄入量显著提高产蛋率,但在35 ℃下增加粗蛋白质摄入量对产蛋率和蛋重无影响。多元回归分析表明,高温下能量摄入量减少可能是产蛋率和蛋重降低的关键性原因。从上述研究以及肉鸡上的研究结果可以推测,高温环境下饲喂高蛋白质水平饲粮可能对蛋鸡产蛋性能无显著影响,饲喂低蛋白质水平饲粮补充氨基酸可能会降低蛋重,而提高能量摄入量可能有效缓解高温的不利影响。
综上所述,较高循环温度(短期至35.6~37.7 ℃)显著降低蛋鸡的采食量、蛋重和体重,影响蛋壳品质,其影响低于或与31~32 ℃持续高温的影响相似。符合生产实际的低循环温度(27~30 ℃)的影响还需进一步研究。高温环境下通过补充脂肪提高能量摄入量可能提高蛋鸡的产蛋性能,提高饲粮粗蛋白质水平可能对缓解高温的影响无显著效果。高温环境下蛋鸡适宜的能量、粗蛋白质和氨基酸水平还有待进一步研究。
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*Corresponding author, associate professor, E-mail: fjh6289@126.com
(责任编辑 田艳明)
Effects of High Ambient Temperature on Performance of Laying Hens and the Mitigation Results of Nutritional Measures
DIAO Huajie1,2FENG Jinghai1*DIAO Xinping2
(1.InstituteofAnimalSciences,ChineseAcademyofAgriculturalSciences,Beijing100193,China; 2.CollegeofAnimalScienceandTechnology,NortheastAgriculturalUniversity,Harbin150030,China)
Summer heat is an important factor influencing the performance of laying hens. However, with popularity of wet curtain and fans cooling system in recent years, the temperature in hen house can generally be controlled below 30 ℃ during summer, and therefore, the negative effects of the high temperature was often ignored in the actual production. The paper payed the attention on the harmful effects of high temperature especially cyclic high temperature on production of laying hens and summarized the measures to relieve the adverse effects of heat stress by changing the dietary energy and crude protein levels, in order to attach importance to the summer heat by researchers in production, and provide a scientific basis for reasonable diet preparation and breeding management of laying hens at the high temperature season.[ChineseJournalofAnimalNutrition, 2017, 29(6):1850-1855]
high temperature; laying hens; performance; nutritional regulation
10.3969/j.issn.1006-267x.2017.06.004
2016-11-21
国家“十二五”科技支撑课题(2012BAD39B02);国家重点研发计划课题“肉禽舒适环境的适宜参数及限值研究”(2016YFD0500509);中国农业科学院科技创新工程(ASTIP-IAS07)
刁华杰(1989—),男,河南商丘人,硕士研究生,动物营养与饲料科学专业。E-mail: huajie0933@163.com
*通信作者:冯京海,副研究员,硕士生导师,E-mail: fjh6289@126.com
S831.4
A
1006-267X(2017)06-1850-06