Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2009 Dec;92(12):5937-50. doi: 10.3168/jds.2008-1959.
Overfeeding prepubertal heifers may impair mammary parenchymal growth and reduce milk production, but evidence suggests that increased intake of a high-protein milk replacer before weaning may be beneficial. This study was designed to evaluate effects of milk replacer (MR) composition on mass and composition of mammary parenchyma and fat pad, growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis gene expression, and putative mammary epithelial stem cells. Specifically, we hypothesized that positive effects of faster rates of gain during the preweaning period alter the development, persistence, or activity of populations of putative mammary epithelial stem cells, possibly through involvement of GH/IGF-I axis molecules. Twenty-four newborn heifers were fed 1 of 4 MR diets (n = 6/diet): control [20% crude protein (CP), 21% fat MR fed at 441 g of dry matter (DM)/d], high protein, low fat (28% CP, 20% fat MR fed at 951 g of DM/d), high protein, high fat (27% CP, 28% fat MR fed at 951 g of DM/d), and high protein, high fat+ (27% CP, 28% fat MR fed at 1,431 g of DM/d). Water and starter (20% CP, 1.43% fat) were offered ad libitum. Animals were killed on d 65 and mammary tissue was subjected to biochemical, molecular, and histological examination. No differences in mammary parenchymal mass or composition, with or without adjusting for empty body weight, were detected. Mass was increased and composition of the mammary fat pad was altered by nutrient intake. No diet differences in putative mammary epithelial stem cell abundance or abundance of transcripts for genes of the GH/IGF-I axis were detected. In this study, growth of the mammary epithelium, size of the mammary epithelial stem cell population, and components of the GH/IGF-I axis did not depend on diet. However, an underlying positive correlation between telomerase, a marker of mammary stem cells, and growth of the mammary parenchyma was detected. Implications of diet-induced effects on mammary fat pad and possible effects on subsequent development and function remain to be determined.
过量喂养青春期前的小母牛可能会损害乳腺实质的生长并降低产奶量，但有证据表明，在断奶前增加高蛋白牛奶代用品的摄入量可能是有益的。本研究旨在评估牛奶代用品（MR）组成对乳腺实质和脂肪垫的质量和组成、生长激素（GH）/胰岛素样生长因子-I（IGF-I）轴基因表达和潜在的乳腺上皮干细胞的影响。具体而言，我们假设在断奶前期间更快的增重速度会改变潜在的乳腺上皮干细胞群体的发育、持续存在或活性，这可能通过涉及 GH/IGF-I 轴分子。24 头新生小母牛被喂食 4 种 MR 饮食中的 1 种（n = 6/饮食）：对照[20%粗蛋白（CP），21%脂肪 MR 每天喂食 441 克干物质（DM）]、高蛋白、低脂肪（28% CP，20%脂肪 MR 每天喂食 951 克 DM）、高蛋白、高脂肪（27% CP，28%脂肪 MR 每天喂食 951 克 DM）和高蛋白、高脂肪+（27% CP，28%脂肪 MR 每天喂食 1431 克 DM）。水和起始饲料（20% CP，1.43%脂肪）自由采食。动物于第 65 天被处死，乳腺组织进行生化、分子和组织学检查。无论是否根据空体重调整，乳腺实质的质量或组成均无差异。营养摄入增加了乳腺脂肪垫的质量，改变了其组成。在潜在的乳腺上皮干细胞丰度或 GH/IGF-I 轴基因的丰度方面，饮食之间没有差异。在这项研究中，乳腺上皮的生长、乳腺上皮干细胞群体的大小以及 GH/IGF-I 轴的组成不依赖于饮食。然而，检测到端粒酶（乳腺干细胞的标志物）与乳腺实质生长之间存在潜在的正相关。需要确定饮食诱导的对乳腺脂肪垫的影响及其对随后的发育和功能的可能影响。
