The Effect Of Two Dietary Levels Of Yeast, Yeast Se And Their Joint Action On Heat Stress In Cow

The purpose of this thesis is to study the effect of two dietary levels of yeast, yeast Se and their joint action on lactation performance and serun biochemical parameter of dairy COWS. To discuss the reaction who can better control of endotoxin into the serun and who can provide better lactation performance. Forty eight during d 120 to d 200 after postpartum, health, milk yield were 18 kg to 22 kg Holstein dairy COWS in mid-lactation, which have similar milk yield,lactation period and parity ,were divided randomly into four groups: group A (selenium yeast group), group B (yeast group), group C (control group) and group D (selenium yeast and yeast group). Test diets were obtained by adding yeast (2 g kg^-1) or yeast Se (0.30 g kg^-1). During the experiment, the average temperature and temperature-humidity index (THI) were 27.4℃(22-33.5℃) and 77.32 (73.6-81.5), respectively.1. The average milk production was lowest in dairy cows fed the control diet. Comparing with control group, group A increased by 5.83 % (P > 0.05), group B increased by 2.22 % (P > 0.05), group D increased by 8.36 % ( P < 0.05).2. The average milk fat and milk protein of dairy cows in test group were higher than the dairy cows in control group. Comparing with control group, the milk protein in group A increased by 4.0 %( P > 0.05), group B increased by 7.7 %( P < 0.05), group D increased by 9.6 %( P < 0.05).The milk fat in group A increased by 1.0 %(P > 0.05), group B increased by 3.7 % (P > 0.05), group D increased by 3.7 % ( P < 0.05). 3. Comparing with control group, dairy cows body temperature in experimental group A, B, D decreased by 0.33℃(P > 0.05), 0.27℃(P > 0.05), 0.47℃(P < 0.05).4. Diets supplementing selenium yeast or yeast can increase DMI of dairy cows. Comparing with control group, DMI of dairy cows in experimental group A, B, D increased by 3.24% (P > 0.05), 5.13% (P < 0.05), 10.05% (P < 0.05).5. Comparing with control group and A guoup, rumen PH of dairy cows in other experimental group significantly increased at 20 days (P < 0.05) and very significantly increased at 40 days (P < 0.01).6. Group A and D were very significantly increased on the level of Selenium in serun comparing with group C and B at 19 days (P < 0.01), but there are no significant changes before 19 days (P > 0.05).7. Group A and D were very significantly increased on the level of GSH-PX and MOD in serun comparing with control group and group B. It shows that selenium yeast improved the GSH-PX activity and reduced the content of MOD in plasma.8. Plasma endotoxin content of dairy cows in group A, B and D were very significant lower than in control group (P < 0.01). Group A very significantly dropped (P < 0.01) and group B significantly dropped (P < 0.05) comparing with group D. Before 29 days, group D were very significant different with the other three groups on the level of plasma endotoxin content (P < 0.01).