Study Of The Metabolizable Glucose Requirement On Holstein Cow Under Heat Stress

This experiment was conducted to study the effect of dietary metabolizable glucose(MG) level on performance, physiological indexes and blood indexes of dairy cows under heat stress. The season of the experiment was in summer(august to september) and the place was at Hongya in Sichuan. One-factor experiment was designed and sixteen healthy dairy cows was selected to be the experimental animal. The cows with similar parity(2-3 parity), days in lactation(199.75±7.46d), milk yield and body weight(546.19±18.37 kg) were randomly divided into four groups with four cows in each group. Cows in test groups 1 to 4 were fed experimental diets containing 121.31,109.70,99.27 and 89.55g/kg MG, respectively. The experiment lasted for six weeks, including a 14-day pre-experiment period and a 28-day experiment period. During the experiment time, all cows were fed twice a day in same yard and milking meanwhile. Measured and recorded temperature and humility in oxtall every day. The indexes would be tested is feed intake, milk yield, rectal temperature, respiratory rate and cortisol, blood sugar, endotoxin in serum. The results showed as follows:during the experiment time the temperature-humidity index(THI) could make dairy stay in heat stress state(the whole period average of THI was 75.03); rectal temperature and respiratory rate of dairy cows between each groups at every time point had no significant different (P>0.05); but the result of the whole experiment time showed that the second group’s rectal temperature was significantly lower than the rest of the group and the third group’s respiratory was significantly lower than the rest of the group. The intake of dairy cows in the third group was significantly higher than other group (P<0.05), and it was the same result of the milk yield. The milk fat percentage of the dairy cows in the third group was significantly higher than other group(P<0.05) at the later period of the experiment and it was the same result in the whole experiment time; the milk protein percentage of the dairy cows had no significantly difference between each group at any time point(P>0.05), but in the whole experiment time the third group was significantly higher than other group(P<0.05); the lactose percentage of dairy cows had no significantly difference between each group at any time point(P>0.05), but in the whole experiment time the first group was significantly higher than other group(P<0.05); the milk dry matter of the third group was significantly higher than the first group(P<0.05), but there was no significantly difference between the rest of other group(P>0.05) and in the whole experiment time the third group was significantly higher than other group(P<0.05). The content of the cortisol, blood sugar and endotoxin in each group had no significantly difference(P>0.05). This research conclusions is that the content of MG in dietary may reduce the rectal temperature and respiratory of dairy cow under heat stress; and it can increase food intake and milk yield significantly; the whole average result showed that it can improve the milk composition of dairy. So it can alleviate dairy heat stress effectively and improve the physiological indexes of dairy cow and enhance production performance of dairy cow under heat stress.Above all the content of MG in dietary can improve the food intake and milk yield but not significantly affect the physiological indexes and milk composition and blood sugar and endotoxin and cortisol of late stage of lactation dairy cow under heat stress. This experiment demonstrates that the best of group content 99.27 g/kg MG. Therefore the composition of dietary of dairy cow under heat stress can be considered by MG. Thereby the dairy heat stress can be alleviate and reducing the harm of heat stress to dairy cow.