| The characteristic of the dairy cow thermoregulation was base on environment and nutrition administration technology. Study regressions of dairy cow physiology on ambient temperature(Ta), effective temperature(ET) and temperature-humidity index(THI), the difference between the high and low yield dairy cow of the circadian rhythm about thermoregulatory at hot summer, evaluated the efficiency of half open and open dairy barn preventing heatstroke, evaluated the efficiency of temperature dropdown by sprinkler and air-cooling fan. The thesis was described in the following three sections.Effect of ambient temperature(Ta), effective temperature(ET) and temperature-humidity index(THI) on rectal temperature(RT), respiration rate(RR), mean skin temperature(mTs) and mean body temperature(Tb) , respectively, were analyzed and the relationship between Tr, Tb and RR, mTs were studied to analyze thermoregulatory of dairy cows. The results were as follows: regression indexes of Tr, RR, mTs and Tb on Ta were 0.13℃, 2.9/min, 0.20℃, 0.142℃, and on ET were 0.19℃, 4.5 /min, 0.26℃, 0.189℃, and on THI were 0.12℃, 2.8/min, 0.17℃, 0.124℃, respectively. The upper threshold temperature was the lowest at 22:00. Regression indexes of Tr, RR, mTs on Tb were 0.99 ℃, 16/min and 1.02℃. Regression indexes of RR, mTs on Tr were 15.7/min and 0.84℃. So at hot summer night, Tr, RR and mTs of dairy cows were always rising to promote heat loss and the heat load was very heavy.The characteristic of thermoregulatory of high and low producing dairy cow after a period of lasting high temperature were analyzed. And the characteristic of physiology and production were compared at different stages: short-term heat stress, lasting heat stress, convalescence and recovery. When ambient temperature was 34.9℃ at lasting heat stress stage, the milk yield of high and low yield dairy dropdown by 6.4 kg/d and 5.7 kg/d, and Tr and respiration rate of the high yield dairy cows were raised to 40.4℃ and 84.9/min which were higher than that of low yield dairy cows. At short-term stress, Tr and RR of high yield dairy were the highest at 22:00. Performance was almost recovery after recovery period, Trof high and low yield dairy cows were 38.9℃ and 38.8℃, respectively, the milk yield of high yield dairy arrived to 24.8kg/d. At hot summer, the high performance dairy with high body temperature can quickly responses to environment and recovery ability quickly, too. Traditional thermotolerant indexes have being deficiency.To evaluate the efficiency of temperature dropdown by sprinkler and air-cooling fan in thermal environment of half and whole open dairy barn, and find the key technology of preventing heat stress at hot summer. In the first stage, when environment temperature arrived to 37.5℃, Ta of A and B dairy barn was 35.5 and 36.7℃, respectively. And at the same time Tr was higher than 39.5℃. Specially, the high yield dairy in A barn raised to 41 ℃ at 22:00 and RR was 90/min, the RR of low yield dairy was 65/min at this time. mTs was 37.6℃ at 15:00. In the third stage, Ta of the barn was higher than outside when outside Ta was lower than 27.6℃. When the ambient temperature was lower than 28℃, the Tr of low yield dairy was between 38.5 and 39℃; if the Ta was down to 24℃, Tr of high yield dairy was lower than 39℃. Ta was dropped down by 2.4℃ when opening air-cooling fan and Ta was lower than outside by 3.2℃, the trend was going up and the difference of the highest temperature was 5.2℃. Ta was dropped down by 1.4 to 2.0℃ after opening sprinkler when Ta higher than 35℃, When the Ta is up to 24℃ and 28℃, high and low yield dairy cows must be cooling, respectively. We prospect the efficiency of air-cooling fan was better than sprinkler. |
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