Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173 Hannover, Germany.
J Steroid Biochem Mol Biol. 2010 Jul;121(1-2):304-7. doi: 10.1016/j.jsbmb.2010.03.084. Epub 2010 Apr 22.
For monogastric animals, changes in dietary protein content modulate calcium (Ca) metabolism by changing parathyroid hormone and calcitriol concentrations. However, the effects of dietary nitrogen (N) restriction on Ca metabolism are not known in ruminants. Since ruminants express endogenous recycling mechanisms very efficiently to save N, it is known that these recycling mechanisms protect ruminants against N depletion in times of dietary N restriction. Therefore, consequences on Ca metabolism induced by reduction of dietary N supply as observed in monogastric animals should not occur in ruminants. Due to this specific metabolic feature, a reduction of dietary N intake can be used to diminish environmental N pollution. The aim of the present study was to determine the consequences of a reduced N intake on Ca homeostasis and respective regulatory hormone concentrations in ruminants. Growing goats fed with a reduced N diet showed a decrease in ionised calcium (Ca2+) and total Ca concentrations while bone resorption marker carboxyterminal cross-linked telopeptide of type I collagen increased in plasma. Unexpectedly, despite hypocalcemia, concentrations of calcitriol were decreased in the animals of the N reduction group whereas calcidiol levels were not affected. From this data, it can be concluded that the Ca metabolism of growing goats can be modulated by changes of dietary N content like in monogastric animals.
对于单胃动物来说，日粮蛋白质含量的变化通过改变甲状旁腺激素和 1,25-二羟维生素 D3 的浓度来调节钙代谢。然而，在反刍动物中，日粮氮（N）限制对钙代谢的影响尚不清楚。由于反刍动物非常有效地表达内源性再循环机制来保存 N，因此已知这些再循环机制可在日粮 N 限制时保护反刍动物免受 N 耗竭的影响。因此，在单胃动物中观察到的由于减少日粮 N 供应而引起的 Ca 代谢变化不应发生在反刍动物中。由于这种特殊的代谢特征，减少日粮 N 摄入可用于减少环境 N 污染。本研究的目的是确定减少 N 摄入对反刍动物钙平衡和相应调节激素浓度的影响。用低 N 日粮喂养的生长山羊表现出离子钙（Ca2+）和总 Ca 浓度降低，而血浆中骨吸收标志物 I 型胶原羧基端交联肽增加。出乎意料的是，尽管存在低钙血症，但 N 减少组动物的 1,25-二羟维生素 D3 浓度降低，而 25-羟维生素 D3 水平不受影响。从这些数据可以得出结论，日粮 N 含量的变化可以像在单胃动物中一样调节生长山羊的钙代谢。
