乳牛口服大量β-胡萝卜素对维生素D3及钙磷代谢的影响

６头健康成年荷斯坦乳牛被随机均分为２组。试验组牛第１周每头口服β－胡萝卜素２３．０ｇ，以后每周每头口服１１．５ｇ，对照组不做任何处理。试验期共８周。结果表明，试验组乳牛血清钙及无机磷水平呈下降趋势；血清维生素Ｄ３活性代谢产物２５－ＯＨ－Ｄ３和１，２５－（ＯＨ）２－Ｄ３均呈现明显下降；至第５周末，血液β－胡萝卜素水平最高，２５－ＯＨ－Ｄ３水平下降非常明显。据此认为，乳牛对β－胡萝卜素的吸收存在一阈值，大剂量的β－胡萝卜素进入机体，可能直接干扰维生素Ｄ３的羟化，使其活性代谢产物呈下降趋势，但由于吸收阈值的存在，其对维生素Ｄ３和骨骼钙磷代谢的干扰作用可得到一定程度的减缓。

Effects of Oral Administration of Overdose Beta-carotene on Metabolism of Vitamin D3

Six healthy and adult dairy cows were selected out from a suburan farm in Beijing and randomly divided into two groups of there cows each. A overdose of betacarotene was administered orally in experimental group. The results showed that the concentration of serum calcium and inorganic phosphorus decreased gradually. The concentration of serum vitamin D3 active metabolites (25OHD3 and 1,25(OH)2D3) decreased significantly and serum carotene reached the highest level at the midstage. The results indicated that the excessive concentration of carotene would inhibit the function for the liver and kidney to turn vitamin D3 into 25OHD3 and 1,25(OH)2D3, and affect the absorption and metabolism of bone calcium and phosphorus.