中文摘要：

为了阐明日粮添加过瘤胃维生素D对围产期奶牛低钙血症的调控机制,在某集约化奶牛场选取40头奶牛,随机分为4组,对照组（C）饲喂基础日粮,试验Ⅰ、Ⅱ、Ⅲ组分别于产前10d至分娩后10d在日粮中每天添加1.5、3.0、6.0g/头过瘤胃维生素D。对4组试验奶牛围产期（分别于产前10、7、3、0d和产后3、7、10d）血清维生素D3（1,25-（OH）2D3）、钙、羟脯氨酸、甲状旁腺素和降钙素水平进行检测。结果表明,围产期奶牛血钙水平分娩时达最低,产后逐渐上升,且产前7d至产后10d对照组奶牛血钙浓度显著低于试验Ⅰ组（P〈0.05）;分娩当天试验Ⅰ组奶牛血浆中1,25-（OH）2D3、羟脯氨酸和降钙素水平显著高于对照组（P〈0.05）,甲状旁腺素水平显著低于对照组（P〈0.05）。提示,日粮中每天添加1.5g/头过瘤胃维生素D能调节甲状旁腺素和降钙素等激素的分泌,促进肠道对钙的吸收,动员骨钙,从而防止奶牛产后低钙血的发生,且围产期奶牛低血钙症与机体血钙稳态调节作用密切关联。

英文摘要：

To understand the regulation mechanism of rumen-protected vitamin D on dairy cows hypocalcaemia in transi- tion period, in the experiment, forty cows from an intensive dairy farm were divided randomly into four groups （the control group （C）, test Ⅰ ,Ⅱ , and Ⅲ groups, 10 cows per group） according to the different dosage of rumen protected vitmin D （0, 1.5, 3.0 and 6.0 g per day for each cow） supplemented into diet from day 10 before calving to parturition. And plasma bio- chemical and endocrinic parameters （1, 25 （OH）2D3 , Ca, hypocalcaemia （HYP）, parathyroid hormone （PTH） and calcitonin （CT））were measured at 10, 7, and 3 d before calving parturition, at parturition,and at day 7, 14, and 21 postpartum. Results showed that level of plasma Ca was the lowest at parturition, and increased gradually after calving in all groups. Test I group had higher plasma Ca from 7 d before calving parturition to 10 d postpartum, compared with the control group （P%0.05）, the concentration of 1, 25-（OH）2D3, HYP and CT in test J group were higher than the control group at parturition （P〈0.05）, the concentration of PTH was lower than the control group （P〈0.05）. Conclusion indicated protective vitamin D added into diet in transition period might be concern with regulation of plasma PTH and CT, which could enhance absorption of calcium in intestinal tract, stimulate mobilization of bone calcium, and then prevent hypoca[cemia at postpartum, and effect of 1.5 g dos age of rumen protected vitamin D was the best. Dairy cows＇ hypocaleaemia in transition period was closely associated with blood calcium homeostatic regulating action.