Influence Of Oxidative Stress Induced By High Temperature On Follicular Development Of Laying Hens

High temperature inhibits follicular development of laying hens, however the mechanism iscomplicated. High temperature could inhibit follicular development by reducing feed intake, affectinggonadotropic hormone or ovarian function, however the mechanism of influence on ovarian function isunknown. Heat stress could induce hens oxidative stress, Supplement of VE could alleviate oxidativedamage induced by high temperature and the inhibition of egg production. So we suppose that hightemperature could inhibit follicular development by reducing oxidative stress. In order to verify thisspeculation we conducted three experiments.1. Influence of daily cyclic high temperature on oxidative stress and follicar development of layinghensOne hundred and eighty Hy-line Brown hens of27weeks of age were randomly divided into threegroups: normal thermal group （NT,28℃）, daily cyclic high temperature group （HT,28-35-28℃） anddaily cyclic high temperature supplemented with VE group （HT+VE,28-35-28℃）. The laying henswere fed either a basal diet （NT, HT） or the basal diet supplemented with250IU/kg vitamin E （HT+VE）.The result showed that daily cyclic high temperature inhibited follicular development， mainlymanifested as decreasing in laying rate （P<0.05）, ovarian weight （P<0.05）, large follicular number（P<0.05）, as well as lower level of expression of P450scc mRNA （P<0.05） and E2, P4content in serum（P<0.05）, which demonstrated that high temperature could influence the follicular development throughinhibiting the function of granulosa cell. Daily cyclic high temperature induced hens oxidative damagemanifested as the increase of MDA concentration （P<0.05）. In the HT+VE group, MDA concentrationin plasma, liver tissue and egg yolk dropped markedly （P<0.05） compared to the HT group, and theinhibition of follicular development was alleviated, which demonstrated that VE might alleviate theinhibition of follicular development through alleviation of the oxidative damage. This suggested that theinhibition of high temperature on follicle development may be related to oxidative stress.2. Effect of oxidative stress induced by tBHP on the follicular development of laying henThirty six Hy-line Brown hens of27weeks of age were randomly divided into three groups:control group, oxidative stress group （tbHP） and oxidative stress with VE group （tbHP+VE）.0.75%sodium chloride （control group） and400μmol/kg tbHP （tbHP, tbHP+VE） was injected byintraperitoneal injection, hens were fed on basal diet in control and tbHP groups, while basal dietsupplemented with250IU/kg VE in tbHP+VE group. The result showed that MDA concentration（P<0.05） in plasma, liver tissue and egg yolk was higher and SOD activity （P<0.05） was lower in tbHPgroup compared with control group. In addition, tbHP decreased ovarian weight （P<0.05）, largefollicular number （P<0.05）, as well as E2, P4content （P<0.05） in serum and expression of P450sccmRNA （P<0.05） in F₁and F₃,which demonstrated that tbHP inhibited follicular development. IntbHP+VE group MDA concentration dropped markedly （P<0.05） compared to tbHP group, and theinhibition of follicular development had been alleviated. All above results demonstrated that oxidative stress might inhibit follicular development.3. Influence of high temperature on oxidative stress of follicular granulosa cells and cellproliferation and differentiationThe cultured granulosa cells in vitro were divided into three groups: optimum temperature group（NT:39℃）, high temperature group （HT,44℃） and high temperature supplemented with VE group（HT+VE:44℃,30μg/ml VE）. The results showed that high temperature significantly increased theROS level, MDA concentration and reduced SOD activity （P<0.05） as well as the expresstion ofLHRmRNA, P450scc mRNA and P4secretion （P<0.05）. The30μg/ml VE alleviated the oxidative stressinduced by high temperature and increased the proliferative activity of granulosa cells. It showed thathigh temperature induced granulosa cells oxidative stress and influenced the granulosa cell proliferationand their ability of progesterone secretion. This suggested that the inhibition of heat stress on theproliferative activity of granulosa cells might be related to oxidative stress.In conclusion, environmental high temperature can induce follicular granulosa cells oxidativestress, thereby affecting the proliferation and differentiation of granulosa cell, leading to folliculardevelopment blocked, it is one of the mechanisms of environmental temperature affect the laying rate.