奶牛热应激缓解剂效果及机制初探

The Preliminary Study on Effect and Mechanism of Heat Stress Alleviators for Dairy Cows

根据胎次、泌乳天数、产奶量将临床健康、平均泌乳146 d、产奶量17.49 kg/头.d的74头中国荷斯坦泌乳牛随机配对分为2组,试验牛集中饲养于同一栋棚舍式拴系牛舍中,按照前后交叉试设计,每期预饲期7 d,正式试验期21 d,前后试验间歇期15 d。试验期牛舍平均温度为31.07℃,温湿指数(TH I)为82.61。对照组饲喂基础日粮,试验组在此基础上添加1%奶牛热应激缓解剂。结果表明:1.试验组体温较对照组显著降低(P<0.05),呼吸和脉搏也有降低的趋势,但差异不显著(P>0.05);2.试验组干物质进食量(DM I)较对照组提高6.4%(P<0.05),4%FCM奶量较对照组提高5.41%(P<0.05),乳脂率、乳蛋白率和乳总固体物含量差异不显著(P>0.05);3.试验组血液一氧化氮合酶(NOS)活性较对照组显著提高(P<0.05),诱导型一氧化氮合酶(iNOS)活性显著降低(P<0.05),热应激缓解剂可能的作用机制是一方面提高热应激期奶牛血液结构型一氧化氮合酶(cNOS)活性,随之激活CM产生短时效适量的NO,使外周血管舒张,机体通过血流将体内的热量运至皮肤进行蒸发散热;另一方面减弱奶牛的甲状腺活动,降低代谢率,减少产热量。

Seventy-four middle lactation Chinese Holstein dairy cows with about 146 days in milk were paired by parity and calving date. Pairs were then assigned randomly to one of two dietary regimens： 1） control group; or 2） fed heat stress alleviators at 1% of the dietary dry matter （DM）. The experiment used in a cross-over design was diets with two 21-day experimental periods with 7-day pre-fed periods at the end of each experimental periods. Half the animals were fed each diet in period 1, and diets were reversed in period 2. The cows were all housed in a tied-stall and stanchion barn, temperature and humidity index （THI） in the trial period averaged 31.07℃ and 82. 61, respectively. The results were as follows： 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 （P〉0. 05） ; 2. 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）; 3. The activity of NOS in serum increased significantly （P〈0. 05）, the activity of iNOS in serum decreased significantly （P〈0. 05）, 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 by stimulating CaM. NO could make the diastole of the peripheral blood vessel so as to bodily heat could be transported to the skin to evaporate, on the other hand, it could weak the activity of thyroid gland of dairy cow, reduce the metabolic rate to decrease the amount of the body heat.