Annen E L, Fitzgerald A C, Gentry P C, McGuire M A, Capuco A V, Baumgard L H, Collier R J
Department of Animal Sciences, University of Arizona, Tucson 85721, USA.
J Dairy Sci. 2007 Jan;90(1):165-83. doi: 10.3168/jds.S0022-0302(07)72618-8.
Objectives were to determine effects of continuous milking (CM) and bovine somatotropin (bST) administration on 1) mammary epithelial cell (MEC) proliferation, apoptosis, and ultrastructure during late gestation and early lactation, 2) expression of genes associated with proliferation, and apoptosis in mammary epithelial cells, and 3) milk yield and composition. Second-gestation, first dry-period cows were randomly assigned to either continuous bST throughout late gestation and early lactation (+bST; n = 4) or no bST (-bST; n = 4) administration. Within each animal, udder halves were randomly assigned to CM or a 60-d dry period (control) treatment. Daily milk yield and weekly milk composition were measured during the last 60 d of gestation in CM halves and from 1 to 30 d postpartum for both halves. Mammary biopsies were obtained at -20 +/- 7, -8 +/- 3, +1 +/- 0, +7 +/- 0, and +20 +/- 0 d (mean +/- standard error) relative to parturition. Prepartum half-udder milk yield was greater in +bST cows than in -bST cows (9.9 vs. 8.2 kg/d) and postpartum half-udder milk yields were dramatically reduced in CM halves compared with control halves (10.6 vs. 22.2 kg/d), regardless of bST treatment. Proliferation of MEC was reduced in CM halves at -8 d (2.7 vs. 5.4%). Apoptosis of MEC was elevated during early lactation for d +1 and +7 in control halves, but was only increased at d +1 in CM halves. Turnover of MEC was not affected by bST. Ultrastructure data indicated complete involution of the control half and lactation maintenance in CM glands (d -20). By d -8, control tissue contained alveoli in an immature secretory state, but CM tissue contained both lactating and immature alveoli. Postpartum ultrastructure parameters were similar between halves until d 20 when control tissue was composed of a homogeneous population of lactating alveoli, but CM tissue contained lactating, engorged, and resting alveoli. Expression of CCAAT/enhancer binding protein-beta (CEBP-beta), cyclin D1, and bcl(2) were up-regulated during late gestation, but did not differ between control and CM halves. Expression of alpha-lactalbumin was increased in CM halves during late gestation, but was not different in CM and control tissue after parturition. Other genes evaluated (bax, insulin-like growth factor binding protein 5, ATP-binding cassette 1, and p27) were not differentially expressed at any timepoints evaluated. Results indicate that CM reduced subsequent half-udder milk yield in primiparous cows through altered MEC turnover and secretory capacity. Negative effects of CM on the subsequent lactation were not alleviated by bST supplementation.
目的是确定持续挤奶（CM）和注射牛生长激素（bST）对以下方面的影响：1）妊娠后期和泌乳早期乳腺上皮细胞（MEC）的增殖、凋亡及超微结构；2）乳腺上皮细胞中与增殖和凋亡相关基因的表达；3）产奶量和乳成分。处于第二个妊娠期、首次干奶期的奶牛被随机分为两组，一组在整个妊娠后期和泌乳早期持续注射bST（+bST组，n = 4），另一组不注射bST（-bST组，n = 4）。在每头动物体内，乳房的两半被随机分配接受CM处理或60天干奶期（对照）处理。在妊娠的最后60天，对接受CM处理的乳房一半测量每日产奶量，对两侧乳房从产后第1天至第30天测量每周乳成分。在相对于分娩的-20±7、-8±3、+1±0、+7±0和+20±0天（平均值±标准误）采集乳腺活检样本。+bST组奶牛产前半侧乳房产奶量高于-bST组奶牛（9.9 vs. 8.2 kg/d），且无论bST处理如何，与对照侧相比，CM侧产后半侧乳房产奶量显著降低（10.6 vs. 22.2 kg/d）。在-8天时，CM侧MEC的增殖减少（2.7% vs. 5.4%）。在泌乳早期，对照侧MEC在第+1天和+7天凋亡增加，但CM侧仅在第+1天增加。MEC的更新不受bST影响。超微结构数据表明对照侧完全退化，而CM腺体维持泌乳状态（第-20天）。到第-8天时，对照组织含有处于未成熟分泌状态的肺泡，但CM组织含有泌乳和未成熟的肺泡。产后直到第20天，两侧乳房的超微结构参数相似，此时对照组织由均匀的泌乳肺泡组成，但CM组织含有泌乳、充盈和静止的肺泡。CCAAT/增强子结合蛋白β（CEBP-β）、细胞周期蛋白D1和bcl(2)在妊娠后期表达上调，但对照侧和CM侧之间无差异。α-乳白蛋白在妊娠后期CM侧表达增加，但产后CM组织和对照组织中无差异。评估的其他基因（bax、胰岛素样生长因子结合蛋白5、ATP结合盒1和p27）在任何评估时间点均无差异表达。结果表明，CM通过改变MEC更新和分泌能力降低了初产奶牛随后的半侧乳房产奶量。补充bST并不能缓解CM对随后泌乳的负面影响。
