Department of Basic Animal and Veterinary Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 7, DK-1870 Frederiksberg C, Denmark.
J Dairy Sci. 2010 Apr;93(4):1478-90. doi: 10.3168/jds.2009-2422.
Milk production is generally lower but lactation persistency higher in primiparous (PP) than in multiparous (MP) goats. This may be related to differences in development and maintenance of mammary gland function, but the underlying mechanisms are not well understood. The present study aimed to elucidate whether differences in lactational performance between PP and MP mammary glands are related to the time course of development and maintenance, not only of the mammary epithelial cell (MEC) population, but also of the mammary vasculature that sustains synthetic activity. Mammary biopsies were obtained from both mammary glands of 3 PP and 6 MP (>or=2 parity) dairy goats at parturition (d 1), d 10, 60, and 180 of lactation. Gene transcription relating to MEC turnover and vascular function was quantified by real-time reverse transcription-PCR, mammary morphology was characterized (quantitative histology), and cell turnover was determined (terminal deoxynucleotidyl transferase dUTP nick end labeling assay and Ki-67). Primiparous glands showed higher expression for the genes involved in angiogenesis; namely, vascular endothelial growth factor receptor 2, and angiopoietin 1 and 2 and their receptor, a few days after parturition (d 10). Primiparous glands also had higher rates of MEC proliferation in early lactation. It therefore appears that initiation of lactation is associated with development and growth of the mammary gland into early lactation, which continues for a longer period in PP compared with MP glands. In addition, MEC survival was found to be higher in PP glands throughout lactation, and MEC in PP glands underwent more extensive differentiation. This could explain the reported flatter lactation curve and higher lactation persistency in PP glands. Although some of the genes included in this study were differentially expressed in PP and MP glands during the course of lactation, it was not possible to identify any specific genomic factor(s) that could account for the differences between PP and MP glands with respect to mammary development and MEC survival during lactation. It remains to be established why parity number affects MEC and vascular development and survival during lactation, and, in particular, which regulatory mechanisms are involved.
奶牛产奶量一般较低，但初产（PP）奶牛的泌乳持久性高于经产（MP）奶牛。这可能与乳腺功能发育和维持的差异有关，但潜在机制尚不清楚。本研究旨在阐明 PP 和 MP 乳腺泌乳性能的差异是否与乳腺上皮细胞（MEC）群体的发育和维持时间有关，不仅与 MEC 群体有关，还与维持合成活性的乳腺血管有关。在分娩（第 1 天）、第 10 天、第 60 天和第 180 天泌乳时，从 3 头初产和 6 头经产（≥2 胎）奶牛的两侧乳腺采集乳腺活检。通过实时逆转录-PCR 定量转录与 MEC 更替和血管功能相关的基因，对乳腺形态进行特征描述（定量组织学），并确定细胞更替（末端脱氧核苷酸转移酶 dUTP 缺口末端标记测定和 Ki-67）。初产乳腺在分娩后几天（第 10 天），血管内皮生长因子受体 2、血管生成素 1 和 2 及其受体等参与血管生成的基因表达较高。初产乳腺在泌乳早期也具有较高的 MEC 增殖率。因此，泌乳的启动似乎与乳腺在早期泌乳时的发育和生长有关，与 MP 乳腺相比，PP 乳腺的这种发育和生长持续时间更长。此外，在整个泌乳期，PP 乳腺中的 MEC 存活率较高，PP 乳腺中的 MEC 经历了更广泛的分化。这可以解释报告中 PP 乳腺的泌乳曲线更平坦和泌乳持久性更高的原因。尽管在泌乳过程中，本研究中包括的一些基因在 PP 和 MP 乳腺中差异表达，但尚无法确定任何特定的基因组因素可以解释 PP 和 MP 乳腺在泌乳期间乳腺发育和 MEC 存活方面的差异。仍需确定胎次如何影响泌乳期间的 MEC 和血管发育和存活，特别是涉及哪些调节机制。
