热应激对奶牛生理和免疫功能的影响及其机理

Effects and Mechanism of Heat Stress on Physiological and Immune System in Dariy Cows

奶牛热应激综合征是指奶牛受到超过本身体温调节能力的高温刺激而产生的非特异性防御反应。奶牛发生热应激后会激活体内的下丘脑—垂体—肾上腺轴,改变机体的神经内分泌调节网络,引起奶牛体内皮质醇激素和多种激素水平变化,协同作用于机体以抵抗热应激对自身的影响;此外,热应激奶牛采食量和消化率普遍降低,营养物质摄入不足,机体处于能量负平衡状态。在这种状态下,奶牛会通过增加体内糖、脂肪和蛋白质的代谢来为机体提供能量从而缓解热应激。然而,严重热应激会导致奶牛代谢功能紊乱及免疫系统损伤,最终导致奶牛消化率、产奶量、繁殖率下降,而疾病易感风险性增加,从而影响奶牛生产的经济效益,给畜牧业带来巨大的经济损失。目前,关于奶牛热应激的研究较多,且多集中于产奶性能和繁殖性能等方面,而有关生理和免疫机能的研究报道较少。作者阐述了奶牛发生热应激时皮质醇激素的变化和调节、三大代谢过程的改变及免疫细胞和相关细胞因子的表达分泌等过程,旨在更加深入地了解热应激对奶牛生理状态及免疫功能的影响,从而为奶牛热应激综合征的防控、诊断和治疗提供理论依据。

Heat stress syndrome of dairy cows refers to the non-specific defense response of dairy cattle induced by stimulation of high temperature which exceeding the body temperature regulation zone.While suffering the heat stress,dairy cows will activate the mechanism of hypothalamus-pituitary-adrenal axis and change the body＇s neuroendocrine regulation network,causing cortisol and some other hormones levels change.All of these procession synergized in the body to reduce the influence of heat stress;In addition,after heat stress,the feed intake and digestibility of dairy cows are generally reduced,and result the body is under nutrition and in a negative state of energy balance.So the cow need to increase the body glucose,fat and protein metabolism to provide more energy to relieving heat stress.However,severe heat stress will lead to dairy cows metabolic disorder and immune system damage,then leads to a decrease of digestibility,milk production,reproduction efficiency,and increases the risk of disease susceptibility,finally it takes an negative effect on economic benefits of dairy cow production and huge economic losses in livestock husbandry.At present,most studies in dairy cows heat stress are focused on milk production and reproductive performance,while few reports on physiological and immune function of dairy cows.In current paper,the secretion and regulation of cortisol,the disorder of the three metabolic processes and the expression and secretion of immune cells and cytokines were talked about indairy cows heat stress.The aim of the paper was to provide theoretical basis for prevention and control,diagnosis and treatment of heat stress syndrome in dairy cow by understanding the effects of heat stress on the physiological status and immune function.