Studies On The Regulatory Mechanism Of Animal Own Anti-heat Stress

Today, the dominant breed in Dairy industry is Holstein. The biological characteristics of Holstein are able to bear cold and unable to endure hot. In Summer, intake is reduced and milk production is also decreased by 15%⁴0%, and milk quality is also decreased by heat stress. The percentage of morbidity and unqualified milk are substantial increased. The obstacles of reproductive are increased, which causes significant economic losses.This study was conducted to determine the anti-heat-stress mechanism of dairy cow , according to the analysis of the effect and mechanism of NOS activity and NO concentration during heat stress period, and to detect the rule of HSP70 and iNOS immunity histochemistry and cell apoptosis in the tissue of rat and bull-calf spleen and liver during the period of heat stress recovering, furthermore, this study was available for us to provide with the theoretical basis for alleviating heat stress and cultivating the breed of anti-heat-stress cow.Experiment 1: the objective of this experiment was to determine the effect and mechanism of NOS activity and NO concentration in serum during heat stress period (THI 82.61), then 20 healthy Chinese Holstein cow and 20 Holstein×Jersey cow were randomly selected. the result was showed as follow: (l)There had a strong relationship between NOS activity(U/ml) and NO concentration (μmol/L) in serum and dairy cow anti-heat-stress mechanism. NOS activity(U/ml) and NO concentration (μmol/L) in dairy cow's serum was decreased significantly(P<0.05) under heat stress. it could make the systole of heart and improve the ability of blood circulation, so the effect of heat stress could be alleviated. (2) the iNOS activity (U/ml)of Holstein×Jersey F₁ serum was significantly lower(P<0.05) than that of Holstein cow, therefore, The activity of serum iNOS could be used as an indicator of blood biochemistry in evaluating the dairy cow anti-heat ability.Experiment 2: 42 SD male rats of 6 months old were randomly divided into two groups, namely control group and heat stress group, to research the changes of HSP70 and iNOS immunity histochemistry in spleen and liver tissue, the rats were chose to receive lh(THI 82) heat stress then 6 stages of recovery in 0-48 h were recorded. The results showed that: (1) the expression of HSP70 in rats spleen tissue was increased with the extension of the recovery time at first, finally returning to normal. After 4 h, the expression of HSP70 in rats spleen tissue reached a peak, and with a large number of cells rupture. After 8 h, the trend of the expression has gradually decreased. After 48 h, the control group was no significant difference (P> 0.05).(2) in the liver tissue, the positive expression of HSP70 in heat stress group and the control group was no significant difference (P> 0.05); (3) The rates of iNOS expression in rat liver cytoplasm reached peak after 8 h. with the positive expression in the vascular endothelial cells, and then gradually declining. In the stage of 48 h, there was no significant difference in the control group (P> 0.05); (4) iNOS expression in spleen, was not obvious either heat stress group or control group.(5) Under heat stress condition, the vitality of iNOS in serum decreased significantly, however increased in liver. When the activity of iNOS in serum decreased and the synthesis of NO reduced, it leaded to increase peripheral resistance. So the blood supply and the function of protecting important tissues increased. And the increased the vitality of iNOS in liver. further strengthen the function of the liver and ensure the effective supply of glucose to the organization under heat stress condition, which could alleviated the effects of heat stress. So. the adequate expression of HSP70 and iNOS in spleen and liver tissue would help the animal to control their own heat stress mechanism. However, the threshold of protective effect in the body of HSP70 and iNOS in heat stress needs to be further exploration.Experiment 3: 6 health China-Holstein bulls of one month old were randomly divided into two groups, namely control group and heat stress group, to study the expression of HSP70 and iNOS after giving 50 min heat stress (THI 89) and 0 h recovery, immunohistochemistry methods was used to study the apoptosis in spleen and liver. The results showed that: iNOS expression in liver was more obvious, and the expression of both HSP70 and iNOS in spleen didn't obvious. The typical apoptosis cells were in spleen, not obvious in liver cell.