饲粮阴阳离子平衡对热应激奶牛机体矿物质代谢的影响

Effects of Dietary Cation-Anion Balance on Mineral Metabolism of Dairy Cows in the Condition of Heat Stress

试验旨在研究饲粮阴阳离子平衡(dietary cation-anion balance,DCAB)对热应激条件下奶牛机体矿物质代谢的影响。采用单因素完全随机试验设计,选取75头健康的泌乳中期[泌乳日龄为(104.8±12.0)d]中国荷斯坦奶牛,根据胎次、产奶量、体重相近的原则随机分为5组(Ⅰ、Ⅱ、Ⅲ、Ⅳ组和对照组),分别饲喂DCAB值为195.76、186.68、177.77、166.94、239.12 m Eq/kg干物质(DM)的饲粮。试验期为67 d,其中预试期7 d,正式试验期60 d。结果表明:对试验期间环境温湿度的监测结果为温湿指数(THI)>72,奶牛处于热应激状态,奶牛直肠温度对照组最高,Ⅰ组最低,呼吸频率随DCAB值的升高而升高,各组之间差异均不显著(P>0.05);通过改变饲粮DCAB值,对奶牛乳中钾(K)、钙(Ca)、镁(Mg)、磷(P)的浓度无显著影响(P>0.05);与Ⅲ、Ⅳ组相比,Ⅰ、Ⅱ组和对照组奶牛乳中钠(Na)的浓度均有不同程度的提高,差异显著(P<0.05),氯(Cl)的浓度显著降低(P<0.05);对奶牛血清中K、Mg、P、Na的浓度影响差异不显著(P>0.05),血清中Ca的浓度随着DCAB值的升高有降低的趋势,而Cl的浓度呈上升趋势;对尿液中K、Ca、Na、Mg的浓度影响差异不显著(P>0.05),与对照组相比,Ⅰ、Ⅱ组的Cl的浓度分别提高了33.826%、35.598%,差异显著(P<0.05);Ⅲ、Ⅳ组分别提高了95.421%、76.957%,差异极显著(P<0.01);尿液p H随着饲粮DCAB值的升高而升高,Ⅰ、Ⅱ组和对照组与Ⅲ、Ⅳ组相比,显著提高(P<0.05)。因此,在热应激条件下,添加阴阳离子平衡盐调整饲粮DCAB值在177.77 m Eq/kg DM以下时,对降低奶牛的呼吸频率、缓解热应激、增加血清Ca浓度效果较好,有利于改善奶牛健康状况。

The trial aimed to study the effects of dietary cation-anion balance （ DCAB） on mineral metabolism of dairy cows in the condition of heat stress. A total of 75 healthy middle lactation [day in milk was （104.8± 12.0） d] China Holstein cows were used in a randomized complete block design and divided into five groups with similar parity, milk yield and weight, i. e. groups Ⅰ, Ⅱ, Ⅲ, Ⅳ and control. The DCAB value in each group was adjusted by providing with different level cation-anion salt. The DCAB values of those groups were 195.76, 186.68, 177.77, 166.94 and 239.12 mEq/kg DM, respectively. The total duration of the experiment was 67 days, the first 7 days of the experiment was the preliminary period and the formal experiment lasted for 60 days. The results showed as follows：the temperature humidity index exceeded 72, and the dairy cows were in heat stress. The rectal temperature of dairy cows in control group was the highest, that in groupⅠwas mini-mum. The breathing rate was increased with DCAB value increase, but no significant difference was observed among groups （ P〉0.05） . The concentrations of K, Ca, Mg, P in milk were not significantly affected by the DCAB value （ P〉0.05） . Compared with the groups Ⅲ and Ⅳ, the concentration of Na in milk in the groupsⅠ, Ⅱ and control was significantly increased （ P〈0.05） , and the concentration of Cl was significantly lower （ P〈0.05） . The effects of DCAB value on the concentrations of K, Mg, P, and Na in serum were not signifi-cant difference （ P〉0.05） , the concentration of Ca in serum was decreased with DCAB value increase, while the concentration of Cl had a upward trend. The concentrations of K, Ca, Na, and Mg in urine were not sig-nificantly affected by DCAB value （P〉0.05）, compared with the control group, the concentration of Cl in groups Ⅰ andⅡ was significantly increased by 33.826% and 35.598% （ P〈0.05） , and that in groupsⅢ andⅣ was significantly increased by 95.421% and 76.957% （ P〈0.01） . The pH of urine was increased with the DCAB value increase, and compared with groupsⅢandⅣ, there was a significant increase in groupsⅠ,Ⅱand control （ P 〈 0. 05 ） . Therefore, adding cation-anion balance salt to adjust DCAB values under 177.77 mEq/kg DM can reduce the respiratory rate and relieve heat stress, and increase Ca level in serum of dairy cows, which would improve the health of dairy cows.