Glucose metabolism in crossbred Holstein cattle feeding on two types of roughage at different stages of lactation

An experiment was performed to study the glucose kinetics of crossbred Holstein cattle feeding on either hay or 5% urea-treated rice straw during early lactation (30 days post partum), mid-lactation (120 days post partum) and late lactation (210 days post partum). Two breeds: Holstein FriesianxRed Sindhi (50:50 = 50% HF) and Holstein FriesianxRed Sindhi (87.5:12.5 = 87.5% HF) were used. In early lactating 87.5% HF animals feeding on either hay or urea-treated rice straw, the high milk yields and lactose secretion were related to glucose uptake by the udder and udder blood flow as compared with those of 50% HF animals. Marked decreases in udder blood flow, glucose uptake, lactose secretion and milk yield were apparent in mid- and late lactation of both groups of 87.5% HF animals. In contrast, both groups of 50% HF animals showed no significant changes in udder blood flow, udder glucose uptake, lactose secretion and milk yields throughout the course of lactation. Total glucose entry rate using 3-[3H] glucose infusion, recycling of glucose carbon and plasma glucose clearance significantly increased during late lactation for 50 and 87.5% HF animals feeding on urea-treated rice straw. The utilization rates of glucose using [U-(14)C] glucose infusion were not significantly different among groups of animals and periods of lactation. It can be concluded that 87.5% HF animals have the genetic potential for a higher milk yield, but a shorter peak yield and poorer persistence in comparison with 50% HF animals. Changes in the utilization of glucose by the mammary gland for milk production in both groups of crossbred animals during feeding on either hay or urea-treated rice straw would be dependent on intramammary changes.     

Histological and histochemical study on mammary gland of Damascus goats through stages of lactation

This research was carried out on seven Damascus goats, to study the relationship between milk production, during advancing lactation, and the changes in secretory mammary cells frequency and cellular activity. Biopsies were obtained from the mammary gland at the three stages of lactation, early, mid and late, for histological and histochemical studies. The histological structures of the mammary gland showed clear differences between lactation stages—being more developed in the early and the mid stages, compared to the late stage of lactation. The number of the alveolar secretory cells increased from the early to the mid stage of lactation by 12.9% and then was reduced at the late stage by 35.9% from that at the mid stage. The milk yield increased by 51.3% from the early to the mid stage, and then was reduced at the late stage by 71.4% from that of the mid stage. The total sectional areas of plate equal to 1.22 mm²/plate of the alveoli were the smallest during late lactation (0.36 mm²/plate) compared to that during the early and the mid stage of lactation (0.50 and 1.17 mm²/plate, respectively). Numerous loci of alkaline phosphatase enzyme (AP) were apparent on the outer surface of the alveolar secretory cells at the early and the mid stages of lactation—suggesting that this enzyme plays an important physiological role in the apical membrane of the alveolar epithelial cells during lactation. Dense protein staining of these cells as well as increased frequency of DNA expression denote great development and increased numbers of these cells at early and mid stages of lactation. This was accompanied by a high level of milk secretion reaching 939.3 ± 130 and 1421.4 ± 123.4 ml/head/day, respectively. In contrast, at the late stage of lactation, the size of alveoli was reduced and few alveoli showed weak AP activity, weak protein manifestation and the lowest frequency of DNA loci. This coincided with the reduction in milk yield (407 ml/head/day). It could be concluded that the stages of the lactation influence the cell number and activity of the mammary parenchyma.     

Effects of evaporative cooling on the regulation of body water and milk production in crossbred Holstein cattle in a tropical environment

The aim of this study was to determine how evaporative cooling modifies body function with respect to water metabolism and other variables relevant to milk synthesis in crossbred cattle. The study was conducted on two groups of 0.875HF:0.125RS crossbred Holstein cattle (87.5%) housed in an open-sided barn with a tiled roof (non-cooled animals) and in a close-sided barn under an evaporative cooling system (cooled animals). The maximum ambient temperature and relative humidity for the non-cooled group were 33 degrees C and 61%, with the corresponding values for the evaporatively cooled barn being 28 degrees C and 84%, respectively. The temperature humidity index (THI) of under non-cooled conditions was higher (P < 0.05) than that in the cooled barn. Rectal temperatures and respiration rates of non-cooled animals were higher (P < 0.05) than those of cooled animals. Daily dry matter intake (DMI) of cooled animals was higher while water intakes were lower (P < 0.05) than those of non-cooled animals. The mean absolute values of plasma volume, blood volume, and extracellular fluid (ECF) of cooled animals were significantly higher (P < 0.05) than those of non-cooled animals throughout all stages of lactation. Milk yields of cooled animals were higher by 42%, 36% and 79% on average than those of non-cooled animals during early-, mid- and late-lactation, respectively. The decline in milk yields as lactation advances was markedly apparent in late-lactating non-cooled animals, while no significant changes in milk composition at different stages of lactation were observed in either group. Mean arterial plasma concentrations, arteriovenous concentration differences (A-V differences) and the extraction ratio across the mammary gland for acetate, glucose and triglyceride of cooled animals were not significantly different compared with values for non-cooled animals. No differences were seen in plasma hormonal levels for triiodotyronine (T(3)) and insulin-like growth factor-1 (IGF-1), but plasma cortisol and thyroxine (T(4)) levels tended to be lower in non-cooled animals. This study suggests that low cooling temperature accompanied by high humidity influences a galactopoietic effect, in part through increases in ECF, blood volume and plasma volume in association with an increase in DMI, which partitions the distribution of nutrients to the mammary gland for milk synthesis. Cooled animals were unable to maintain high milk yield as lactation advances even though a high level of body fluids was maintained during long-term cooled exposure. The decline in milk yield, coinciding with a decrease in net energy for lactation as lactation advances, could be attributed to a local change within the mammary gland.     

High fat diet alters lactation outcomes: possible involvement of inflammatory and serotonergic pathways

Delay in the onset of lactogenesis has been shown to occur in women who are obese, however the mechanism altered within the mammary gland causing the delay remains unknown. Consumption of high fat diets (HFD) has been previously determined to result decreased litters and litter numbers in rodent models due to a decrease in fertility. We examined the effects of feeding a HFD (60% kcal from fat) diet versus a low-fat diet (LFD; 10% kcal from fat) to female Wistar rats on lactation outcomes. Feeding of HFD diet resulted in increased pup weights compared to pups from LFD fed animals for 4 d post-partum. Lactation was delayed in mothers on HFD but they began to produce copious milk volumes beginning 2 d post-partum, and milk yield was similar to LFD by day 3. Mammary glands collected from lactating animals on HFD diet, displayed a disrupted morphologies, with very few and small alveoli. Consistently, there was a significant decrease in the mRNA expression of milk protein genes, glucose transporter 1 (GLUT1) and keratin 5 (K5), a luminobasal cell marker in the mammary glands of HFD lactating animals. Expression of tryptophan hydroxylase 1 (TPH1), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, and the 5-HT(7) receptor (HTR7), which regulates mammary gland involution, were significantly increased in mammary glands of HFD animals. Additionally, we saw elevation of the inflammatory markers interleukin-6 (IL-6) and tumor necrosis factor-α (TNF- α). These results indicate that consumption of HFD impairs mammary parenchymal tissue and impedes its ability to synthesize and secrete milk, possibly through an increase in 5-HT production within the mammary gland leading to an inflammatory process.     

Essential Role for Zinc Transporter 2 (ZnT2)-mediated Zinc Transport in Mammary Gland Development and Function during Lactation

The zinc transporter ZnT2 (SLC30A2) imports zinc into vesicles in secreting mammary epithelial cells (MECs) and is critical for zinc efflux into milk during lactation. Recent studies show that ZnT2 also imports zinc into mitochondria and is expressed in the non-lactating mammary gland and non-secreting MECs, highlighting the importance of ZnT2 in general mammary gland biology. In this study we used nulliparous and lactating ZnT2-null mice and characterized the consequences on mammary gland development, function during lactation, and milk composition. We found that ZnT2 was primarily expressed in MECs and to a limited extent in macrophages in the nulliparous mammary gland and loss of ZnT2 impaired mammary expansion during development. Secondly, we found that lactating ZnT2-null mice had substantial defects in mammary gland architecture and MEC function during secretion, including fewer, condensed and disorganized alveoli, impaired Stat5 activation, and unpolarized MECs. Loss of ZnT2 led to reduced milk volume and milk containing less protein, fat, and lactose compared with wild-type littermates, implicating ZnT2 in the regulation of mammary differentiation and optimal milk production during lactation. Together, these results demonstrate that ZnT2-mediated zinc transport is critical for mammary gland function, suggesting that defects in ZnT2 not only reduce milk zinc concentration but may compromise breast health and increase the risk for lactation insufficiency in lactating women.     

Influence of milking frequency on mammary gland dynamics

The effects of milking frequency on milk production is a key question for the dairy industry. Milk production is related to the number of active alveoli in the mammary gland and movement between active and quiescent alveolar pools is influenced by the milking frequency. In this paper, we analyse a mechanistic model based on known biological inputs that describes the effect of milking frequency on the alveolar composition of the mammary gland. It is shown that the model can qualitatively reproduce the correct alveolar dynamics. We also investigate the model robustness and parameter sensitivity. Additionally, by making the plausible assumption that the senescence rate of alveoli is proportional to the number of quiescent alveoli present, we obtain an analytical solution requiring periodic resetting.     

Expression of alpha-lactalbumin, alpha-S1-casein, and lactoferrin genes is heterogeneous in sheep and cattle mammary tissue.

We used 35S-labeled cRNA probes to localize the sites of alpha-lactalbumin, alpha-S1-casein, and lactoferrin mRNA synthesis in sheep and forcibly weaned cattle mammary tissue. Expression of alpha-lactalbumin was absent in three of four "virgin" glands studied, present in some alveoli of "pregnant" glands but not in others, despite a similar histological appearance. In the early lactating gland, expression was high in those alveoli with few fat globules in their cells and lumen and was absent in alveoli with abundant fat globules. These observations suggest either that alpha-lactalbumin gene expression is linked to the long-term secretory activity of cells and falls once cells are resting or regressing, or that there are cyclical variations in expression, or that in the lactating gland some groups of epithelial cells are synthesizing alpha-lactalbumin and some are synthesizing fat. Expression patterns of alpha-S1-casein were similar to those of alpha-lactalbumin. Lactoferrin, in contrast, was expressed almost exclusively in the "fatty alveoli" of both species. Our results show that dramatic variations in milk gene expression can occur throughout the mammary gland of sheep and cattle and that at no stage of pregnancy, lactation, or involution can the gland be considered metabolically homogeneous.     

Molecular regulation of milk trace mineral homeostasis

The regulation of milk trace mineral homeostasis requires the temporal integration of three main processes, (A) mineral uptake into the secretory mammary epithelial cell (MEC); followed by (B) mineral secretion from MEC into the alveoli lumen of the mammary gland for sequestration in milk; and then (C) milk release in response to suckling. Trace mineral requirements of term infants are generally met by exclusive breast-feeding through about the first 6 months of life and although milk zinc (Zn), iron (Fe), and copper (Cu) concentrations are relatively refractory to maternal trace mineral status, they normally decline throughout lactation. Recently, Zn-, Fe- and Cu-specific transporters have been identified that regulate trace element uptake and efflux in various cell types; however, there is currently little information available regarding the processes through which the mammary gland regulates milk trace mineral transport. The homology of trace mineral transporters between species permits the utilization of rodent models to examine the regulation of mammary gland mineral transport. Therefore, we have used the lactating rat to determine changes in mammary gland Zn, Fe and Cu transporter expression and localization that occur throughout lactation and in response to maternal trace mineral deficiency in hope of elucidating some of the changes which occur during mammary gland trace element homeostasis and also may be occurring in lactating women.     

e-Cow: an animal model that predicts herbage intake, milk yield and live weight change in dairy cows grazing temperate pastures, with and without supplementary feeding

This animal simulation model, named e-Cow, represents a single dairy cow at grazing. The model integrates algorithms from three previously published models: a model that predicts herbage dry matter (DM) intake by grazing dairy cows, a mammary gland model that predicts potential milk yield and a body lipid model that predicts genetically driven live weight (LW) and body condition score (BCS). Both nutritional and genetic drives are accounted for in the prediction of energy intake and its partitioning. The main inputs are herbage allowance (HA; kg DM offered/cow per day), metabolisable energy and NDF concentrations in herbage and supplements, supplements offered (kg DM/cow per day), type of pasture (ryegrass or lucerne), days in milk, days pregnant, lactation number, BCS and LW at calving, breed or strain of cow and genetic merit, that is, potential yields of milk, fat and protein. Separate equations are used to predict herbage intake, depending on the cutting heights at which HA is expressed. The e-Cow model is written in Visual Basic programming language within Microsoft Excel^R. The model predicts whole-lactation performance of dairy cows on a daily basis, and the main outputs are the daily and annual DM intake, milk yield and changes in BCS and LW. In the e-Cow model, neither herbage DM intake nor milk yield or LW change are needed as inputs; instead, they are predicted by the e-Cow model. The e-Cow model was validated against experimental data for Holstein–Friesian cows with both North American (NA) and New Zealand (NZ) genetics grazing ryegrass-based pastures, with or without supplementary feeding and for three complete lactations, divided into weekly periods. The model was able to predict animal performance with satisfactory accuracy, with concordance correlation coefficients of 0.81, 0.76 and 0.62 for herbage DM intake, milk yield and LW change, respectively. Simulations performed with the model showed that it is sensitive to genotype by feeding environment interactions. The e-Cow model tended to overestimate the milk yield of NA genotype cows at low milk yields, while it underestimated the milk yield of NZ genotype cows at high milk yields. The approach used to define the potential milk yield of the cow and equations used to predict herbage DM intake make the model applicable for predictions in countries with temperate pastures.     

Pten对奶牛乳腺上皮细胞活力及乳蛋白合成的影响

Pten作为抑癌基因,参与调控细胞生长、粘附、凋亡以及其它细胞活动.目前,国内外关于Pten在奶牛乳腺发育过程中表达及调节的研究鲜有报道.为了揭示Pten的表达与奶牛乳腺发育与泌乳之间的关系,本研究应用qRT-PCR技术检测Pten在不同泌乳时期和不同乳品质的奶牛乳腺组织中的表达差异,进而应用脂质体转染方法,通过siRNA介导的RNA干扰技术改变Pten基因在奶牛乳腺上皮细胞中的表达量,CASY法检测细胞活力,用ELISA试剂盒检测细胞分泌β-酪蛋白的含量,采用qRT-PCR、Western 印迹等技术检测Pten对奶牛乳腺上皮细胞中乳蛋白相关信号通路基因表达的影响.结果显示,泌乳期高乳品质奶牛乳腺组织中Pten表达水平显著低于泌乳期低乳品质及干乳期奶牛;Pten基因沉寂后,细胞活力提高,β-酪蛋白质量浓度增加,CSN2、AKT、MTOR、STAT5表达量增加.研究表明,Pten可通过抑制细胞活力和乳蛋白分泌而影响泌乳.     

Origin,concentration and structural features of human mammary gland cells cultured from breast secretions

Summary This study traced the origin of cells observed in human breast secretion samples obtained during lactation and describes the appearance of these cells following prolonged maintenance in vitro. Human milk contains a large number of single vacuolated foam cells and a small proportion of non-vacuolated epithelial cells in clusters. Foam cells are identified by their large size, the polarity of their cytoplasmic organelles, the variation in number and size of lipid vacuoles and the condensed chromatin of their eccentrically located nucleus. Both cell types originate by exfoliation from the mammary gland. This was established by comparing the structural characteristics of cells isolated from milk with those of the cuboidal cell linings of ducts and alveoli in lactating mammary tissue. Relatively pure populations of foam cells could be established from early lactation samples (3–7 days post/partum) while non-vacuolated epithelial cell clusters were more frequently cultured from late lactation specimens (1–10 days postweaning). Foam cells did not divide and lost cytoplasmic organization during prolonged culture. In contrast, non-vacuolated epithelium in clusters proliferated to form colonies of polygonal cells. These results, which imply that foam cells are an active form of the non-vacuolated mammary cells in clusters, call attention to one system for the study of the complex hormonal interactions necessary to induce and maintain lactation.Supported in part by NCI contract NO 1-CB-33898     

Comparative 2D-DIGE Proteomic Analysis of Bovine Mammary Epithelial Cells during Lactation Reveals Protein Signatures for Lactation Persistency and Milk Yield

Mammary gland is made up of a branching network of ducts that end with alveoli which surrounds the lumen. These alveolar mammary epithelial cells (MEC) reflect the milk producing ability of farm animals. In this study, we have used 2D-DIGE and mass spectrometry to identify the protein changes in MEC during immediate early, peak and late stages of lactation and also compared differentially expressed proteins in MEC isolated from milk of high and low milk producing cows. We have identified 41 differentially expressed proteins during lactation stages and 22 proteins in high and low milk yielding cows. Bioinformatics analysis showed that a majority of the differentially expressed proteins are associated in metabolic process, catalytic and binding activity. The differentially expressed proteins were mapped to the available biological pathways and networks involved in lactation. The proteins up-regulated during late stage of lactation are associated with NF-κB stress induced signaling pathways and whereas Akt, PI3K and p38/MAPK signaling pathways are associated with high milk production mediated through insulin hormone signaling.     

Mammary growth patterns in guinea pigs during puberty, pregnancy and lactation

Mammary gland growth patterns were studied in 110 guinea pigs during the growth phase, pregnancy and lactation. Body weight changes were studied and, in addition, mammary indices were wet weight, dry fat-free tissue (DFFT), deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Statistical analyses were mathematical regression models to best fit the actual data. These included linear, quadratic, cubic, and several forms of exponential regression models. Data were separated into growth phase (60 guinea pigs in 10 age groups), pregnancy (20 guinea pigs in 4 groups), and lactation (30 guinea pigs in 6 groups). Data during pregnancy and the first 5 days of lactation were pooled and analyzed also because mammary growth continued beyond pregnancy to Day 5 of lactation. Mammary wet weight increased according to a cubic expression in the growth phase, while mammary DFFT, DNA and RNA were rectilinear through 200 days of age. During pregnancy and the first 5 days of lactation, mammary growth parameters followed the pattern of an exponential equation. Daily rates of increase for mammary DFFT and DNA were twice the rate for mammary wet weight. During lactation, mammary gland indices increased to Day 5 and then decreased gradually from Day 10 to Day 20. The best mathematical models for these change were those which are used to describe lactation curves, but all mammary gland indices decreased later and more gradually than milk production. Comparisons in growth rates of guinea pig mammary glands were made with those published for dairy goats and dairy cows. Rates of mammary DNA changed inversely to lengths of gestation in these 3 species.