| According to parity, calving day and daily milk yield, 74 healthy Chinese Holstein dairy cows with average milk production of 17.49 kg/head·day at a 146-day milking period after calving were randomly allotted to 2 groups,each group was 37 cows.the experiment design was a cross-over design. The cows were collectively housed in a tied-stall and stanchion barn for 70 days. Temperature and temperature and humidity index (THI) in the trial period averaged 31.07℃ (24.71℃~34.96℃) and 82.61 (76.77~87.28) respectively. The treatment group was supplemented 1% heat stress alleviators and the basic diet is the same.The result were showed as follow: 1. comparing with control group, dairy cows body temperature in experimental group decreased significantly (P<0.05), breathe and pulse also decreased to some extent but didn't differ significantly(P>0.05); dry matter intake (DMI) increased by 6.4%(P<0.05); 4% fat corrected milk(FCM) in experimental group increased by 5.41%(P<0.05), milk fat, milk protein, and solid contents didn't differ significantly(P>0.05); the activity of NOS in serum increased significantly (P<0.05), the activity of iNOS in serum decreased significantly (P<0.05), the concentrations of NO in serum didn't differ significantly(P>0.05); the activity of T-AOC, SOD, GSH-PX, and the concentration of MDA, albumin, total protein didn't differ significantly(P>0.05) between two groups; In the heat stress period, the possible mechanisms of heat stress alleviators may be as follows: on the one hand, it enhanced greatly the activity of cNOS in peripheral blood, and it stimulated the appropriate amount of NO in a short-term. NO could make the...
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