热应激期日粮添加酵母铬对奶牛产奶性能及血液生化指标的影响

根据胎次、泌乳期和产奶量,按随机单位组方法将44头泌乳120 d,日均产奶量为27.70 kg的奶牛分为4组,每组11头.预饲期15 d,正试期45 d,试验期温湿指数为81.5.对照组饲喂基础日粮,试验Ⅰ、Ⅱ、Ⅲ组在基础日粮中添加酵母铬(精料中,Cr的质量分数分别为0.40、0.80、1.20 mg.kg-1),研究热应激期日粮添加酵母铬对奶牛产奶性能及血液生化指标的影响.结果表明:试验组奶牛产奶量较对照组均有不同程度提高,其中以试验Ⅱ组效果最佳,提高6.26%(P<0.05),试验Ⅰ、Ⅲ组有升高的趋势,但差异不显著(P>0.05);试验Ⅱ、Ⅲ组血清游离三碘腺原氨酸(FT3)含量和FT3与游离甲状腺素(FT4)的比值(FT3/FT4)较对照组极显著降低(P<0.01);试验Ⅰ组血清胰岛素活性较对照组显著升高(P<0.05),试验Ⅱ、Ⅲ组有升高的趋势,但差异不显著(P>0.05);试验Ⅰ组日粮干物质进食量(DM I)较对照组显著提高(P<0.05),但随着Cr含量的增加,DM I提高的趋势逐渐减弱;各试验组奶样中Cr含量符合NY5045-2001卫生标准.

Effects of dietary supplementation of chromium yeast on the performance and blood biochemical parameters in heat-stressed dairy cows

According to parity,calving day,daily milk yield,forty-four healthy dairy cows with average milk yield of 27.7 kg·d~(-1) per cow at a 120 day milking period after calving were randomly divided into four dietary groups(control,treatments Ⅰ,Ⅱ and Ⅲ).Temperature and humidity index(THI) in the trial period averaged 81.50.The dairy cows were pre-fed with a commercial diet for 15 days;thereafter the formal experiment lasted for 45 days,in which,the control animals were fed with basic diets,and the animals in treatment Ⅰ,Ⅱ and Ⅲ were fed with the diets supplemented with chromium in mass fractions of 0.40,0.80,1.20 mg of mg·kg~(-1) from chromium yeast,respectively.Comparing with the control group,application of chromium yeast increased milk yields to some extent,but a significant rising was shown only in treatment Ⅱ(6.3%,P<0.05);the serum concentration of free triiodothyronine(FT_3) and the ratio of FT_3 to free thyroxine(FT_4) were reduced significantly in treatment Ⅰ and Ⅱ(P<0.01);and insulin level rose comparatively in treatment Ⅰ(P<0.05).Supplying chromium yeast at the Cr level of 0.40 mg·kg~(-1) in concentrates could significantly increase the dry matter intake(DMI) of heat-stressed dairy cows.However,this effect could not be observed when increasing the dosages.Although chromium yeast was applied during summer heatstress period(Cr 0.40-1.20 mg·kg~(-1) in concentrates),the chromium content in experimental milk accorded with the standard recommended by Chinese government(NY 5045-2001).