Esser N M, Hoffman P C, Coblentz W K, Orth M W, Weigel K A
Department of Dairy Science, University of Wisconsin, Madison 53706, WI, USA.
J Dairy Sci. 2009 Apr;92(4):1741-9. doi: 10.3168/jds.2008-1789.
Phosphorus requirements, as percent of dietary dry matter for heifers (0.20-0.35%) and endogenous levels of P in feeds (0.20-0.35% of dry matter) are similar, suggesting that supplementation of P in heifer diets may be infrequently required. Because long-term studies are unavailable, 183 Holstein heifers and 182 Holstein x Jersey crossbred heifers were fed diets with (0.39%) and without (0.29%) supplemental P from 4 to 21 mo of age in a replicated pen design. Two subpopulations of heifers were selected mid-trial for intensive measurement of bone development and metabolism. Thirty-two heifers at 628 d (+/-10.0 d) of age, balanced by breed and diet, were evaluated for bone development. External frame measurements included hip height, length, heart girth, hip width, cannon bone circumference, pelvic length, pelvic height, and pelvic width. Tails of heifers were surgically amputated with the 13 and 14th coccygeal vertebrae retained. After tissue removal, the 13th coccygeal vertebrae were scanned using peripheral quantitative computed tomography with cortical, trabecular, and total bone densities determined. A second subpopulation (n = 64) of heifers (375 d +/- 33 d), balanced for breed and diet, were evaluated for serum pyridinoline and osteocalcin to assess systemic bone metabolism. Data were analyzed as a completely randomized design with breed, treatment, and their interaction in the model. External skeletal measurements revealed significant differences in hip height, hip width, heart girth, cannon bone circumference, and pelvic length between Holstein and crossbred heifers. Supplementing P had no effect on external frame measurements, bone density, or bone metabolism markers. Bone P content was lower (18.1 vs. 18.6%) in heifers fed no supplemental P. Data suggest P supplementation to heifers modestly increased bone P content but increased bone P was not reflected in frame growth, bone density, or bone metabolism.
小母牛对磷的需求量（占日粮干物质的0.20 - 0.35%）与饲料中磷的内源水平（占干物质的0.20 - 0.35%）相似，这表明小母牛日粮中可能很少需要补充磷。由于缺乏长期研究，183头荷斯坦小母牛和182头荷斯坦×泽西杂交小母牛在4至21月龄时，采用重复栏舍设计，分别饲喂添加（0.39%）和不添加（0.29%）补充磷的日粮。在试验中期选择两个小母牛亚群进行骨骼发育和代谢的强化测量。对32头628日龄（±10.0天）的小母牛进行骨骼发育评估，这些小母牛按品种和日粮进行了平衡。外部体格测量包括体高、体长、胸围、髋宽、管骨周长、骨盆长度、骨盆高度和骨盆宽度。小母牛的尾巴在手术中被截断，保留第13和第14尾椎。组织去除后，使用外周定量计算机断层扫描对第13尾椎进行扫描，测定皮质骨、小梁骨和总骨密度。对第二个小母牛亚群（n = 64）（375日龄±33天）进行血清吡啶啉和骨钙素评估，以评估全身骨骼代谢，这些小母牛按品种和日粮进行了平衡。数据采用完全随机设计进行分析，模型中包括品种、处理及其交互作用。外部骨骼测量显示，荷斯坦小母牛和杂交小母牛在体高、髋宽、胸围、管骨周长和骨盆长度方面存在显著差异。补充磷对外部体格测量、骨密度或骨代谢标志物没有影响。不补充磷的小母牛骨骼磷含量较低（18.1%对18.6%）。数据表明，给小母牛补充磷适度增加了骨骼磷含量，但增加的骨骼磷并未反映在体格生长、骨密度或骨代谢上。
