Influence Of Temperature-humidity Index In Different Seasons On Performance, Physiological And Biochemical Parameters Of Cows

This trial was conducted to study the trend of THI in different seasons and the effects of the THI on performance, physiological and biochemical parameters of dairy cows in Sichuan. There were 4 groups in the study: spring, summer, autumn and winter. Twelve Holstein dairy cows at mid-lactation during every season were used according to fetal degree, avoirdupois and age. The experiment period last for 1 year.The results showed that: (1) It is extremely significant deviation during 4 seasons in Sichuan. The THI of cowhouse was 77.16±2.11 in summer; Rectal temperature and breath rate of dairy cows in summer were extremely significantly higher(P<0.01) than that in the other three seasons. Dairy cows in summer showed chronic heat stress, without in other seasons. (2) DMI and milk production in summer were significant decreased (P<0.05); Compared with spring, autumn and winter, when THI increased 1 unit, DMI in summer reduced 0.32 kg, 0.07 kg and 0.20 kg, respectively, and milk production with 0.36 kg, 0.23 kg and 0.11 kg. Milk SCC was greater (P< 0.05), there was a declined trend (P>0.05) of milk fat ratio and milk protein ratio. Performance and milk quality were not significantly influenced by the variance of THI in the other three seasons. (3) The metabolism function of dairy cows in summer was decreased and that in the other three seasons was not significantly influenced by the variance of THI. In summer: the content of serum T3, T4, glucose and the activity of ALP were extremely significant lower(P<0.01); The content of serum BUN was extremely significant increased(P<0.01); The content of serum E2 and PRL were significant increased(P<0.05).(4) The antioxidance function of dairy cows in summer was lower and that in the other three seasons was not significantly changed. The activity of serum SOD and GSH-PX of dairy cows in summer were significant decreased(P<0.05), the content of MDA in summer was extremely significant increased(P<0.01). (5) The serum heat stress indexes of dairy cows in summer were significant influenced by the variance of THI, without in other seasons. The content of serum CK and HSP70 of dairy cows in summer were extremely significant increased(P<0.01), the content of Cor was significant lower(P<0.05).In concluding, THI was 77.16±2.11 in summer in Sichuan, Rectal temperature and breath rate of dairy cows in summer were significant increased, dairy cows in summer showed chronic heat stress. In summer, the antioxidance function and metaboilic level of dairy cows was lower, carbohydrate and protein were influenced, performance and milk quality was decreased. Performance and milk quality of dairy cows in other seasons were not significant influenced.