Taylor M S, Knowlton K F, McGilliard M L, Seymour W M, Herbein J H
Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315, USA.
J Dairy Sci. 2008 Jun;91(6):2408-16. doi: 10.3168/jds.2007-0750.
Twenty-seven multiparous Jersey cows were randomly assigned to receive an oral bolus containing corn starch (control, CON), corn starch plus 15 mg of 25-hydroxyvitamin D(3) (25-OH), or 15 mg of cholecalciferol (D(3)) at 6 d before expected parturition. Cows were maintained in individual box stalls from 20 d before expected parturition and fed a common diet. Jugular blood samples were collected at -14, -13, -5, -4, -3, -2, -1 d before expected calving, at calving, and at 1, 3, 5, 7, 9, 11, 13, 28, 56, and 84 d postcalving. After calving, cows were housed in 1 pen in a free-stall barn and consumed a common diet. Colorimetric assays were used to analyze Ca, P, and Mg concentrations in serum. Serum concentrations of osteocalcin (OC), an indicator of bone formation, serum 25-hydroxyvitamin D(3), and parathyroid hormone (PTH) were determined in samples obtained from d -5 through d 13. The 9 control multiparous cows and 5 untreated primiparous cows were used to evaluate the effect of parity on the variables that were measured. There was no effect of parity on Ca, PTH, or 25-OH concentration. Compared with second-lactation cows and older cows (>2 lactations), first-lactation cows had greater serum OC (22.3, 32.0, and 48.3 ng/mL, respectively), indicating that younger animals were forming more bone. Blood Ca, P, and Mg decreased near the time of calving and then increased over time. Serum 25-hydroxyvitamin D(3) was greater for cows dosed with 25-OH (119.0 ng/mL) compared with those dosed with D(3) (77.5 ng/mL) or CON (69.3 ng/mL). Cows dosed with 25-OH tended to have lower serum PTH concentration, but treatments did not affect serum Ca, P, or Mg. Serum OC was greater in second-lactation cows compared with cows entering their third or fourth lactation but OC was unaffected by treatment. Although results indicated a 60% increase in serum 25-hydroxyvitamin D(3) due to a single oral dose of 25-OH before calving, the amount administered in this study apparently was not sufficient for initiation of any improvement in Ca homeostasis at parturition.
27头经产泽西奶牛在预计分娩前6天被随机分配，分别口服含有玉米淀粉的大丸剂（对照组，CON）、玉米淀粉加15毫克25-羟基维生素D(3)（25-OH）或15毫克胆钙化醇（D(3)）。从预计分娩前20天起，奶牛被单独饲养在箱式牛栏中，并饲喂普通日粮。在预计产犊前-14、-13、-5、-4、-3、-2、-1天、产犊时以及产后1、3、5、7、9、11、13、28、56和84天采集颈静脉血样。产犊后，奶牛被安置在自由牛栏中的一个围栏内，并采食普通日粮。采用比色法分析血清中的钙、磷和镁浓度。在从第-5天到第13天采集的样本中测定骨钙素（OC，骨形成指标）、血清25-羟基维生素D(3)和甲状旁腺激素（PTH）的血清浓度。9头经产对照奶牛和5头未处理的初产奶牛用于评估胎次对所测变量的影响。胎次对钙、PTH或25-OH浓度没有影响。与第二胎奶牛和年龄较大的奶牛（>2胎）相比，第一胎奶牛的血清OC更高（分别为22.3、32.0和48.3纳克/毫升），这表明较年轻的动物形成的骨更多。血钙、磷和镁在产犊时附近下降，然后随时间增加。与服用D(3)（77.5纳克/毫升）或CON（69.3纳克/毫升）的奶牛相比，服用25-OH的奶牛血清25-羟基维生素D(3)更高（119.0纳克/毫升）。服用25-OH的奶牛血清PTH浓度往往较低，但处理对血清钙、磷或镁没有影响。与进入第三或第四胎的奶牛相比，第二胎奶牛的血清OC更高，但OC不受处理影响。尽管结果表明，由于在产犊前单次口服25-OH，血清25-羟基维生素D(3)增加了60%，但本研究中给予的剂量显然不足以在分娩时启动钙稳态的任何改善。
