饲粮中添加碘对奶牛产奶性能、垂体——甲状腺轴分泌机能的影响

EFFECTS OF IODINE SUPPLEMENTATION ON MILK PERFORMANCE,HYPOPHYSEAL-THYROID AXIS SECRETION FUNCTION OF DAIRY COWS

选用15头健康成年黑白花奶牛,随机分成三组,按3×3有重复拉丁方设计进行饲养试验,试期三个月,共有三个处理:(A_1)饲粮中添加 K110mg/头·日,(A_2)添加 K120mg/头·日,(A_3)常规饲粮(对照),研究饲粮中添加碘对奶牛产奶性能、垂体——甲状腺轴分泌机能的影响。结果表明:处理 A_1奶牛产奶量和标准乳量分别为23.29±0.51kg/头·日和20.53±0.51kg/头·日,处理 A_2则分别为23.41±0.34kg/头·日和20.58±0.33kg/头·日,均极显著地高于对照 A_3的21.58±0.50kg/头·日和18.70±0.57kg/头·日(P<0.01),A_1、A_2处理之间差异不显著。三处理乳脂率分别为(A_1)3.21±0.077,(A_2)3.20±0.079,(A_3)3.10+0.081,两个补碘处理虽均高于对照,但统计上不够显著。三处理之间乳中干物质含量和非脂干物质含量均未发现显著性差异。A_1、A_2处理血清中 T_4含量均显著高于 A_3(P<0.05),但 A_1、A_2之间无显著差异(P>0.05);血清 T_3含量 A_2极显著地高于 A_3(P<0.01),A_1显著高于 A_3(P<0.05),A_1、A_2之间差异不显著(P>0.05);血清游离甲状腺变化情况与甲状腺素的变化相似。A_1、A_2血清中 TSH 含量均极显著地高于 A_3,但 A_1、A_2之间未发现显著差异(P>0.05)。提示日粮中添加适量碘可以改善奶牛垂体——甲状腺轴的分泌机能从而提高产奶性能,饲粮碘稍微过量对甲状腺机能、产奶性能均无不良影响。

15 Holstein cows at mid-lactation were selected and randomly assigned into three groups of 5 cows in a 3×3 Latin square trial from March 2 to May 30,1989;three treatments were all fed on basal diet supplementing either (A_1) 10 mg KI head per day,(A_2) 20 mg KI head per day or (A_3) no additives ,the control.Dietary iodine supplementation increased milk yield significantly (P<0.01) and milk fat percentage nonsignificanfly,there were no differences between A_1 and A_2 treatment in ei- ther milk yield or milk composition.The concentrations of thyroxine,triiothyronine,thyrotropin and free thyroxine index (FT_4I) in serum were also elevated significantly (P<0.05) by dietary iodine sup- plementation,but no differences in any hormone concentration in serum were found between treat- ments of high and low iodine supplementation (P>0.05).The relationship between thyroid function and milk performance of dairy cows were also discussed.