乳牛口服过量维生素A对维生素D_3及钙磷代谢的影响

STUDY ON THE EFFECTS OF ORAL ADMINlSTRATIONOF VITAMIN A ON METABOLISM OF VITAMIN D.CALCIUM AND PHOSPHORUS IN DAIRY COWS

从北京郊区某农场选取１０头健康成年黑白花乳牛，随机分为试验（５头，每周每头口服维生素Ａ１００万单位）和对照（５头，不作任何处理）两组。８周以后检测发现，试验组血清钙和无机磷水平呈下降趋势；尾椎骨皮质变薄，密度下降，呈现骨质吸收现象；血清碱性磷酸酶（ＡＫＰ）活性则明显上升（Ｐ＜０．０５），共同功酶谱带中骨带染色变宽变深；血清维生素Ｄ＿３水平显著下降（Ｐ＜０．０５）；其活性代谢产物２５－羟维生素Ｄ＿３（２５－ＯＨ－Ｄ＿３）极显著下降（Ｐ＜０．０１）；１，２５－二羟维生素Ｄ＿３［１，２５－（ＯＨ）２－Ｄ＿３］亦呈下降趋势（但差异不显著）。据此，可以证实大量维生素Ａ经口进入机体，可以干扰维生素Ｄ＿３的正常吸收。本试验还首次证实乳牛血清维生素Ａ过量，可以干扰（抑制）肝脏和肾脏对维生素Ｄ＿３的羟化，使其活性代谢产物生成减少，进一步影响钙磷的吸收和代谢，从而造成骨骼的生长和矿化障碍。

Ten healthy and adult dairy cows were selected out from a suburban farm inBeijing and randomly divided into two groups. Each group included five cows. VitaminA (one million I. U. per cow every week) was administered orally in experimental group.After 8 weeks, the results showed that the concentration of serum calcium and inor-ganic phosphorus decreased, but activity of serum alkaline Phosphatase increased mar-kedly (P<0.05), and staining of bone band of its isoenzyme was dark and wide.Thinness of cortex, decrease of density and absorption of substance of bone in tailvertebra were found. The concentration of serum vitamin D, (P<0.05), its active meta-bolites, 25-hydroxycholecalciferol (25-OH-D3) (P<0.01) and 1,25-dihydroxycholeca-lciferol[1,25-(OH)2-D3] (no statistical difference) were decreased. So the results showedthat a large amount of vitamin A in body could interfere with normal absorption ofvitamin D3; The results indicated first that excessive vitamin A in dairy cows couldinhibit the hydroxylation of vitamin D, in the liver and kidney, made the productionof its active metabolites decreased and affected furtber on the absorption and metabolismof calcium and phosphorus. As a result the growth and mineralization of the bone wereinfluenced .