Puvogel G, Baumrucker C R, Sauerwein H, Rühl R, Ontsouka E, Hammon H M, Blum J W
Division of Nutrition and Physiology, Institute of Animal Genetics, Nutrition and Housing, Vetsuisse Faculty, University of Berne, CH-3012 Berne, Switzerland.
J Dairy Sci. 2005 May;88(5):1785-800. doi: 10.3168/jds.S0022-0302(05)72853-8.
Studies in vitro show important interactions among vitamin A, lactoferrin, and insulin-like growth factor (IGF) binding proteins (IGFBP) and, thus, the IGF system. As a consequence, mammary gland epithelial cell proliferation and apoptosis during the bovine dry period and potential milk yield may be affected. We have studied effects of feeding vitamin A (550,000 IU/ d) that exceed daily requirements about 8-fold for up to 2 mo to dairy cows during the dry period on concentrations of retinol and its metabolites in plasma and milk, milk lactoferrin, plasma and milk IGF-I and IGFBP-3, lactoferrin and IGF-I mRNA levels in mammary gland tissue, mammary gland apoptosis, and 100-d milk yield in the ensuing lactation. In the group supplemented with vitamin A, the peripartal decrease of plasma retinol was delayed and attenuated, and colostral retinol plus retinylester concentration was enhanced, but colostral beta-carotene concentration decreased. The retinoic acid isomer 9,13-dicis retinoic acid that coeluted with 13-cis retinoic acid, was the predominant circulating retinoic acid and was higher in GrA than the control group. Plasma IGFBP-3 concentrations were positively correlated with plasma retinol concentrations (r = 0.51), but there were no group differences. Numbers of apoptotic epithelial cells in mammary epithelium were higher at drying off and parturition than in the middle of the dry period, coinciding with high concentrations of IGF-I and lactoferrin in mammary secretions. At parturition, numbers of apoptotic cells in mammary gland biopsies in cows supplemented with vitamin A were higher than in control cows. In conclusion, supplementation of dairy cows during the dry period with high amounts of vitamin A did not significantly modify concentrations of lactoferrin, IGFBP-3, and IGF-I in plasma and in mammary secretions, but slightly decreased energy-corrected 100-d milk yield and milk fat yield, possibly because of enhanced apoptic rates of mammary cells.
体外研究表明，维生素A、乳铁蛋白和胰岛素样生长因子（IGF）结合蛋白（IGFBP）之间存在重要相互作用，进而影响IGF系统。因此，奶牛干奶期乳腺上皮细胞的增殖和凋亡以及潜在产奶量可能会受到影响。我们研究了在干奶期给奶牛补充超过每日需求量约8倍（550,000 IU/天）的维生素A，持续2个月，对血浆和乳汁中视黄醇及其代谢产物的浓度、乳乳铁蛋白、血浆和乳汁中的IGF-I和IGFBP-3、乳腺组织中乳铁蛋白和IGF-I mRNA水平、乳腺细胞凋亡以及随后泌乳期100天产奶量的影响。在补充维生素A的组中，围产期血浆视黄醇的下降延迟且减弱，初乳中视黄醇加视黄酯的浓度升高，但初乳中β-胡萝卜素浓度降低。与13-顺式视黄酸共洗脱的视黄酸异构体9,13-二顺式视黄酸是主要的循环视黄酸，在维生素A补充组中比对照组更高。血浆IGFBP-3浓度与血浆视黄醇浓度呈正相关（r = 0.51），但两组之间无差异。干奶期结束和分娩时乳腺上皮细胞凋亡数量高于干奶期中期，这与乳腺分泌物中高浓度的IGF-I和乳铁蛋白一致。分娩时，补充维生素A的奶牛乳腺活检中的凋亡细胞数量高于对照奶牛。总之，在干奶期给奶牛补充大量维生素A并没有显著改变血浆和乳腺分泌物中乳铁蛋白、IGFBP-3和IGF-I的浓度，但能量校正后的100天产奶量和乳脂产量略有下降，这可能是由于乳腺细胞凋亡率增加所致。
