Milking and feed restriction regulate transcripts of mammary epithelial cells purified from milk

Effects of parity and week after calving on the metabolic, redox and immune status of dairy cows

At the onset of lactation in dairy cows, inflammation and oxidative stress may occur and result in a risk of pathologies and lower milk yield. To propose an innovative management strategy for cows during this period, it is essential to better understand these physiological variations. Our objective was to evaluate the metabolic, redox and immune status of 7 primiparous and 8 multiparous Holstein cows during late gestation and the first months of lactation. Blood samples were collected between 3 weeks before calving until 12 weeks postpartum. Milk samples were also collected, but only at the time points after calving. The metabolic (nonesterified fatty acids (NEFA), BHB, glucose, urea, calcium) and redox (reactive oxygen metabolites (ROM), oxidative stress index (OSI), glutathione peroxidase activity, vitamin E) statuses were analyzed in plasma or erythrocytes. The expression of genes related to antioxidant functions was determined in leukocytes collected from milk. For immune status, plasma cytokine levels and the production of reactive oxygen species (ROS) in classical and regulatory neutrophils were measured in 2 whole blood ex vivo challenges. The data were analyzed using a mixed model that included the fixed effects of parity and week and their interaction. Milk yield, plasma NEFA and BHB in wk 2 and 4 after calving were higher in multiparous cows than in primiparous cows, whereas glucose and calcium tended to be lower. Plasma ROM and OSI levels in wk 8 were higher in multiparous than in primiparous cows. Multiparous cows also displayed higher glutathione peroxidase activity in erythrocytes, and antioxidant transcription factor and superoxide dismutase-1 expression levels in milk leukocytes. Moreover, multiparous cows had higher plasma concentrations of vitamin E but lower plasma levels of cytokines CXCL10, CCL2, IL1Rα and IFNγ. Following ex vivo whole blood stimulation with Escherichia coli, lower IL1α and TNFα levels were measured in multiparous than in primiparous cows. Intracellular ROS production by neutrophils was lower in multiparous than in primiparous cows. These results thus indicated marked physiological changes in wk 8 compared with wk 2 and 4 of lactation. These differences in the physiological status of primiparous and multiparous cows offer interesting perspectives for potential dietary strategies to prevent pathologies which take account of parity and week relative to calving.

Graduate Student Literature Review: The challenge of drying-off high-yielding dairy cows

The cessation of lactation (i.e., dry-off) in dairy cattle is an area of research that has received much focus in recent years. The dry period is necessary to optimize tissue remodeling of the mammary gland, but represents a stressful event, incorporating several changes in daily routine, diet, and metabolism. Moreover, the high milk yields achieved by modern cows in late gestation exacerbate the need for relevant manipulations in the days around dry-off, as excessive accumulation of milk might jeopardize the success of the dry period, with potential negative effects on future lactation. Production levels over 15 kg/d are an additional risk factor for udder health, delay mammary involution, and worsen metabolic stress and inflammatory responses. Furthermore, the pressure to reduce antibiotic usage in farm animals has resulted in increased attention on the dry period, given that historically most dairy cattle were provided prophylactic intramammary antibiotic treatment at dry-off as a means to reduce the risk of intramammary infections in the subsequent lactation. Several strategies have been proposed over the years to cope with these challenges, aiming to gradually reduce milk yield before dry-off, promoting at the same time the start of mammary involution. Among them, the most common are based on feed or nutrient restriction, a decrease in milking frequency, or administration of prolactin inhibitors. These practices have different capacities to reduce milk yield through different mechanisms and entail several implications for udder health, animal welfare, behavior, endocrine status, metabolism, and inflammatory conditions. The present review aims to provide a comprehensive overview of the dry-off phase in high-yielding cows and of the impact of high milk production at dry-off, and to describe possible strategies that might be implemented by farmers and veterinarians to optimize this critical phase in an integrated way.

Effect of different dietary regimens at dry-off on performance, metabolism, and immune system in dairy cows

Concentrate withdrawal and feed restriction are commonly used to reduce milk production and to facilitate dry-off, but may impair immune function in dairy cows. We investigated the effect of feed rations providing different amounts of nutrients in combination with feed restriction on performance, endocrine, and metabolic responses, as well as on leukocyte function before and after abrupt dry-off. Forty-three cows were studied from d 12 before until d 6 after dry-off (56 d before scheduled calving). Cows were fed experimental concentrates rich in crude protein (nitrogenic, n = 14), glucogenic precursors (glucogenic, n = 14), or lipids (lipogenic, n = 15). On d 3 before dry-off, total feed allowance was restricted to 50% in half of the animals of each dietary group, whereas feed allowance remained unchanged in the other animals. Performance parameters (milk yield, milk composition, and dry matter intake) were recorded, and daily blood and milk samples were taken and analyzed for various metabolic and endocrine parameters. Additionally, activity and mRNA abundance of several genes in leukocytes were measured at selected time points before and after feed restriction and dry-off, respectively. Feed restriction immediately resulted in a negative energy balance and decreased milk production. Concomitantly, concentrations of nonesterified fatty acids increased, whereas insulin, insulin-like growth factor-1, and glucagon decreased. After dry-off, energy balance turned positive and plasma nonesterified fatty acids decreased. Plasma glucose, insulin, and insulin-like growth factor-1 concentrations increased in all groups after dry-off. Glucose, insulin, and glucagon concentrations in plasma were higher in nonrestricted compared with restricted animals after dry-off. The experimental concentrate types marginally affected the investigated metabolic and endocrine factors, with the exception of elevated milk and plasma urea concentrations in cows fed the nitrogenic concentrate. Chemotactic and phagocytic activity of leukocytes were not affected by diets, feed restriction, or dry-off. Likewise, blood leukocyte mRNA abundance encoding for tumor necrosis factor α (TNF), heat shock protein family A (HSP70), and the glucose transporters (GLUT) 1 and 3 remained unchanged throughout the study period. Overall, the short-term negative energy balance induced by feed restriction was temporarily accompanied by metabolic adaptations, but did not alter the studied factors related to the immune system. Metabolic and endocrine adaptations supporting milk synthesis were continued during the first days after dry-off despite cessation of milking. Thus, the abrupt dry-off resulted in a short-term increase of glucose and triglyceride concentrations, with a delayed endocrine response to re-establish nutrient homeostasis in blood.

Mammary epithelial cell transcriptome reveals potential roles of lncRNAs in regulating milk synthesis pathways in Jersey and Kashmiri cattle

Background

Long noncoding RNAs (lncRNAs) are now proven as essential regulatory elements, playing diverse roles in many biological processes including mammary gland development. However, little is known about their roles in the bovine lactation process.

Results

To identify and characterize the roles of lncRNAs in bovine lactation, high throughput RNA sequencing data from Jersey (high milk yield producer), and Kashmiri cattle (low milk yield producer) were utilized. Transcriptome data from three Kashmiri and three Jersey cattle throughout their lactation stages were utilized for differential expression analysis. At each stage (early, mid and late) three samples were taken from each breed. A total of 45 differentially expressed lncRNAs were identified between the three stages of lactation. The differentially expressed lncRNAs were found co-expressed with genes involved in the milk synthesis processes such as GPAM, LPL, and ABCG2 indicating their potential regulatory effects on milk quality genes. KEGG pathways analysis of potential cis and trans target genes of differentially expressed lncRNAs indicated that 27 and 48 pathways were significantly enriched between the three stages of lactation in Kashmiri and Jersey respectively, including mTOR signaling, PI3K-Akt signaling, and RAP1 signaling pathways. These pathways are known to play key roles in lactation biology and mammary gland development.

Conclusions

Expression profiles of lncRNAs across different lactation stages in Jersey and Kashmiri cattle provide a valuable resource for the study of the regulatory mechanisms involved in the lactation process as well as facilitate understanding of the role of lncRNAs in bovine lactation biology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08406-x.

A flow cytometric method for measuring and isolating mammary epithelial cells from bovine milk

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Flow cytometry using an antibody against butyrophilin allows quantification of mammary epithelial cells in milk.

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Sorting butyrophilin-positive or CD45-negative cells isolates epithelial cells from milk.

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Selection for cytokeratin was not effective in this flow cytometry application.

Sampling frequent time points of mammary signaling pathways is not possible with tissue biopsies. We have validated a flow cytometry and cell sorting procedure for isolating live bovine mammary epithelial cells from somatic cell populations in milk using butyrophilin 1A1 as a marker for mammary epithelial cells and CD45 as a marker for hematopoietic cells. Hoechst 33342 staining and propidium iodide exclusion were used to select for nucleated live cells. Positive selection of butyrophilin (BTN)-expressing cells was performed by fluorescence-activated cell sorting. Quantitative real-time PCR performed on mRNA isolated from these cells showed a 226-fold increase in κ-casein (CSN3) mRNA expression in BTN single-positive cells compared with unsorted cells, whereas CD45 single-positive cells showed a significant decrease. A negative selection strategy for cells not expressing the hematopoietic cell marker CD45 also resulted in a cell population with a 196-fold increase in CSN3 mRNA expression compared with unsorted cells. We found no enrichment of CSN3 mRNA expression after sorting cells using cytokeratin antibodies. The noninvasive assays described here allow for daily or more frequent sampling time points for measurement of mammary epithelial cells during the course of lactation.

Single nucleotide polymorphisms in the bovine SLC2A12 and SLC5A1 glucose transporter genes - the effect on gene expression and milk traits of Holstein Friesian cows

In this study, novel single nucleotide polymorphisms (SNPs) were found in the 5'-regulatory regions (promoters) of the bovine glucose transporter (GT) genes SLC2A12 and SLC5A1. These polymorphisms were shown to associate with certain milk production traits in HF cows, including milk yield, milk composition, and somatic cell count. It was shown that the SNP g.-671C > G (NC_037336.1: g.72224078C > G) in the SLC2A12 gene could be an effective marker of cattle production traits and that genotypes CC and CG are associated with the best productivity. The polymorphisms found in the SLC5A1 gene promoter also influenced milk production traits in HF cows, albeit to a lesser extent, and we propose that these polymorphisms could be useful as genetic markers for milk production traits in marker-assisted selection (MAS); however, this must be confirmed on larger populations of cattle. In addition, the presence of polymorphisms within promoter regions appears to affect the expression of GT genes in the cow mammary gland and modify transcription factor (TF) binding capacity.

The effect of single-nucleotide polymorphism in the promoter region of bovine alpha-lactalbumin (LALBA) gene on LALBA expression in milk cells and milk traits of cows

Polymorphisms of milk protein genes have been proposed as candidate markers for dairy production traits in cattle. In the present study, a polymorphism was detected in the 5'-flanking (promoter) region of the bovine alpha-lactalbumin (LALBA) gene, a T/C transition located at nucleotide -1,001 relative to the transcription start site g.-1001T > C (NC_037332.1:g.31183170T > C), which is recognizable with PstI restriction endonuclease. In silico analyses showed that this mutation created novel retinoid X receptor alpha and vitamin D receptor transcription factor binding sites. Real-time PCR found that cows with different genetic variants of the promoter demonstrated different levels of expression of LALBA mRNA in milk somatic cells (MSCs). The TT genotype cows demonstrated low expression, whereas those with CT demonstrated much higher expression (P < 0.05). ELISA analysis found milk LALBA protein levels also differed between the TT and CT cows (P < 0.05) and that these levels were not correlated with the mRNA abundance in MSC. Association analysis found that the g.-1001T > C polymorphism in the promoter region of the LALBA gene influenced milk production traits in Polish Holstein-Friesian cows. High daily milk yield and dry matter yield, and high lactose yield and concentration were associated with the TT genotype. The TT genotype cows also had a lower number of somatic cells in the milk, considered as an indicator of udder health status. Therefore, the TT genotype could be more desirable from the breeder's perspective.

Single-cell RNA sequencing of freshly isolated bovine milk cells and cultured primary mammary epithelial cells

Bovine mammary function at molecular level is often studied using mammary tissue or primary bovine mammary epithelial cells (pbMECs). However, bulk tissue and primary cells are heterogeneous with respect to cell populations, adding further transcriptional variation in addition to genetic background. Thus, understanding of the variation in gene expression profiles of cell populations and their effect on function are limited. To investigate the mononuclear cell composition in bovine milk, we analyzed a single-cell suspension from a milk sample. Additionally, we harvested cultured pbMECs to characterize gene expression in a homogeneous cell population. Using the Drop-seq technology, we generated single-cell RNA datasets of somatic milk cells and pbMECs. The final datasets after quality control filtering contained 7,119 and 10,549 cells, respectively. The pbMECs formed 14 indefinite clusters displaying intrapopulation heterogeneity, whereas the milk cells formed 14 more distinct clusters. Our datasets constitute a molecular cell atlas that provides a basis for future studies of milk cell composition and gene expression, and could serve as reference datasets for milk cell analysis.

Effect of feed restriction on dairy cow milk production: a review

In the dairy cow, negative energy balance affects milk yield and composition as well as animal health. Studying the effects of negative energy balance on dairy cow milk production is thus essential. Feed restriction (FR) experiments attempting to reproduce negative energy balance by reducing the quantity or quality of the diet were conducted in order to better describe the animal physiology changes. The study of FR is also of interest since with climate change issues, cows may be increasingly faced with periods of drought leading to a shortage of forages. The aim of this article is to review the effects of FR during lactation in dairy cows to obtain a better understanding of metabolism changes and how it affects mammary gland activity and milk production and composition. A total of 41 papers studying FR in lactating cows were used to investigate physiological changes induced by these protocols. FR protocols affect the entire animal metabolism as indicated by changes in blood metabolites such as a decrease in glucose concentration and an increase in non-esterified fatty acid or β-hydroxybutyrate concentrations; hormonal regulations such as a decrease in insulin and insulin-like growth factor I or an increase in growth hormone concentrations. These variations indicated a mobilization of body reserve in most studies. FR also affects mammary gland activity through changes in gene expression and could affect mammary cell turnover through cell apoptosis, cell proliferation, and exfoliation of mammary epithelial cells into milk. Because of modifications of the mammary gland and general metabolism, FR decreases milk production and can affect milk composition with decreased lactose and protein concentrations and increased fat concentration. These effects, however, can vary widely depending on the type of restriction, its duration and intensity, or the stage of lactation in which it takes place. Finally, to avoid yield loss and metabolic disorders, it is important to identify reliable biomarkers to monitor energy balance.

Effects of L-Histidine and Sodium Acetate on β-Casein Expression in Nutrient-Restricted Bovine Mammary Epithelial Cells

Simple Summary

Nutrient restriction is known to decrease the milk production and milk quality of dairy cows. However, providing cows with abundant nutrients also has a disadvantage because it will increase feed costs. Under such a situation, the use of feed additives can be a good strategy to reduce the feed cost. The objective of this study was to investigate the effects of histidine and sodium acetate on β-casein expression in nutrient-restricted bovine mammary epithelial cells. The results indicate that histidine has the potential to increase the β-casein levels in bovine mammary cells when the nutrient is restricted, suggesting that histidine is a potential feed additive for cows in a nutrient-insufficient environment.

Abstract

Nutrient restriction is a challenging condition for the mammary glands of dairy cows. In this condition, supplementing amino acids and energy sources might be a good strategy to improve the concentration of one of the most important caseins in bovine milk. Therefore, the objective of this study was to investigate the effects of L-histidine (His) and sodium acetate (Ace) in a nutrient-restricted (NR) immortalized bovine mammary epithelial cell line (MAC-T cells). The treatments for the MAC-T cells are as follows: experiment (1) 0–5% diluted basal medium; experiment (2) supplementation of 0–9.6 mM of His or Ace in NR or normal conditions; experiment (3) supplementation of 0–9.6 mM of Ace plus 0.15 mM of His in NR or normal conditions. The 1% diluted medium showed no significant effect on the cell viability with the basal medium; thus, it was selected as the NR condition. The relative expression of β-casein was significantly increased in the NR condition with the inclusion of 0.15 mM His alone or with Ace compared to that in control. The supplementation of Ace increased the β-casein level under normal conditions. However, it did not change the expression of β-casein under the NR condition. The results suggest that His has the potential to increase the β-casein expression under the NR condition.

Effect of Heat Stress on Dairy Cow Performance and on Expression of Protein Metabolism Genes in Mammary Cells

Simple Summary

Environmental temperatures are increasing, and consequent global warming also has negative effects on dairy cattle farms, which may result in reduced production and poorer milk quality. The protein content of casein, in particular, is important in influencing the coagulation properties of milk and, therefore, the production and quality of cheese. The aim of this study was to assess the effect of heat stress on animal performance and on the expression of selected genes involved in milk protein metabolism. Eight dairy cows were kept under thermoneutral conditions for 8 days. The same animals were then maintained under mild heat stress conditions for an additional 8 days. The results of this study revealed that mild heat stress reduced the feed intake and performance of dairy cows in terms of milk and protein yield, but not the expression of the target genes involved in milk protein metabolism, such as those coding for caseins.

Abstract

The aim of this study was to assess the effect of heat stress on dairy cow performance and on the expression of selected genes involved in milk protein metabolism. Eight Italian Holstein Friesian cows were kept under thermoneutral conditions (temperature–humidity index (THI) < 72, CON) for 8 days and under mild heat stress conditions (72 < THI < 78, HS) for an additional 8 days. The rectal temperature, feed intake, and milk yield were recorded during the last 3 days of the CON and HS periods. During the same time period, milk samples were collected to assess the composition and expression of selected genes involved in milk protein metabolism. Gene expression analyses were performed on somatic cells from milk, which are representative of mammary tissue. In terms of dairy cow performance, HS resulted in lower milk and protein yields and feed intake but higher rectal temperature than for CON (p < 0.05). Under HS, there were greater abundances of HSPA1A (p < 0.05) and BCL2 (p < 0.05), compared to CON, but similar levels of CSN2 (p > 0.05), CSN3 (p > 0.05), HSPA8 (p > 0.05), and STAT5B (p > 0.05) mRNA. Mild heat stress reduced the performance of dairy cows without affecting the expression of genes coding for caseins.

Feeding level regulates the expression of some genes involved with programed cell death and remodeling in goat and sheep mammary tissue

Mammary tissue (MT) turnover is characterized by programed cell death and remodeling which might be affected by both feeding level and animal species. Thus, twenty-four dairy goats and the same number of sheep were assigned to three homogenous sub-groups per animal species and fed the same diet in quantities which met 70% (FL70), 100% (FL100) and 130% (FL130) of their daily energy and crude protein requirements. Individual MT samples were taken by biopsy from the animals on the 30th and 60th experimental day. The results showed, in the first sampling time, a significant reduction in the mRNA abundance for selected genes involved in programed cell death in both FL 70 fed goats (STAT3 and BECN1) and sheep (CASPASE8 and BECN1) compared with the respective FL100 groups. The FL130, in comparison with the FL100, caused a significant increase in transcripts accumulation of STAT3 gene in both sampling times and CASPASE8 gene in the second sampling time in goat MT, while the opposite happened for the mRNA expression of CASPASE8 and BECN1 genes in sheep MT, but only in the first sampling time. Moreover, a significant up regulation in the mRNA levels of MMP2 gene in MT of FL130 fed sheep was observed. The FL130, in comparison with the FL70, caused an enhancement in the mRNA expression levels of BECN1, CASPASE8, BAX and STAT3 genes in goat MT only. It was also shown that apoptosis and autophagy can be affected simultaneously by the feeding level. Overfeeding affects MT programed cell death and remodeling by a completely different way in goats than sheep. In conclusion, feeding level and animal species have strong effects on both MT programed cell death (apoptosis and autophagy) and remodeling but the molecular mechanisms need further investigation.

Short communication: Molecular markers for epithelial cells across gastrointestinal tissues and fecal RNA in preweaning dairy calves

The objective of this study was to compare the transcription of gene markers for gastrointestinal (GI) epithelial cells, including fatty acid binding protein 2 (FABP2) and cytokeratin 8 (KRT8), and tight junction complex genes (TJP1, CLDN1, CLDN4) in fecal RNA against several GI tract tissue sections in dairy calves. Eight healthy Jersey calves were euthanized at 5 wk of age, and postmortem samples were collected from rumen, duodenum, jejunum, ileum, large intestine, cecum, and feces for total RNA isolation. Tissues and fecal samples were immediately frozen in liquid nitrogen until RNA isolation. A real-time quantitative PCR analysis was performed using a single standard curve composited of equal amounts of all samples, including cDNA from fecal and GI tract tissues. The mRNA expression of the tight junctions TJP1, CLDN1, and CLDN4 was greater in fecal RNA compared with lower GI tract tissues (i.e., duodenum, jejunum, ileum, large intestine, and cecum). Similar to fecal RNA, rumen tissue had greater expression of tight junctions CLDN1 and CLDN4 than lower GI tract tissues. Similarly, rumen tissue had greater expression of TPJ1 than all lower GI tract tissues except duodenum. The expression of TJP1 and CLDN4 was greater in fecal RNA than in rumen tissue; in contrast, CLDN1 mRNA expression was greater in rumen tissue than in the fecal RNA. The expression of FABP2 was greater in duodenum in comparison to all tissue except ileum. The mRNA expression of FABP2 in fecal samples was similar to jejunum and ileum. The expression of KRT8 in fecal samples was similar to duodenum, large intestine, and cecum. The fecal RNA had a greater expression of KRT8 in comparison to jejunum and ileum. The rumen tissue had the lowest mRNA expression of KRT8. The expression levels of FABP2, KRT8, and tight junction genes observed in fecal transcripts suggest that a considerable amount of RNA derived from GI tract epithelial cells can be detected in fecal RNA, which is in agreement with previous data in neonatal dairy calves and other biological models including humans, rodents, and primates. The greater expression of tight junctions in fecal RNA in comparison to sections of the low GI remains to be understood, and due to the importance of tight junctions in GI physiology, further clarification of this effect is warranted. The similarities in mRNA expression of FABP2 and KRT8 between fecal RNA and intestinal sections add up to the accumulating evidence that fecal RNA can be used to investigate molecular alterations in the GI tract of neonatal dairy calves. Further research in this area should include high-throughput transcriptomic analysis via RNA-seq to uncover novel molecular markers for specific sections of the GI tract of neonates.

Effects of micronutrient supplementation on performance and epigenetic status in dairy cows

The postpartum period is crucial in dairy cows and is marked by major physiological and metabolic changes that affect milk production, immune response and fertility. Nutrition remains the most important lever for limiting the negative energy balance and its consequences on general health status in highly selected dairy cows. In order to analyze the effect of a commercial micronutrient on intrinsic parameters, performances and the epigenome of dairy cows, 2 groups of 12 Holstein cows were used: 1 fed a standard diet (mainly composed of corn silage, soybean meal and non-mineral supplement) and the other 1 fed the same diet supplemented with the commercial micronutrient (µ-nutrient supplementation) for 4 weeks before calving and 8 weeks thereafter. Milk production and composition, BW, body condition score (BCS), DM intake (DMI) and health (calving score, metritis and mastitis) were recorded over the study period. Milk samples were collected on D15 and D60 post-calving for analyses of casein, Na+ and K+ contents and metalloprotease activity. Milk leukocytes and milk mammary epithelial cells (mMECs) were purified and counted. The viability of mMECs was assessed, together with their activity, through an analysis of gene expression. At the same time points, peripheral blood mononuclear cells (PBMCs) were purified and counted. Using genomic DNA extracted from PBMCs, mMECs and milk leukocytes, we assessed global DNA methylation (Me-CCGG) to evaluate the epigenetic imprinting associated with the µ-nutrient-supplemented diet. The µ-nutrient supplementation increased BCS and BW without modifying DMI or milk yield and composition. It also improved calving condition, reducing the time interval between calving and first service. Each easily collectable cell type displayed a specific pattern of Me-CCGG with only subtle changes associated with lactation stages in PBMCs. In conclusion, the response to the µ-nutrient supplementation improved the body condition without alteration of global epigenetic status in dairy cows.

Impact of post-ruminally infused macronutrients on bovine mammary gland expression of genes involved in fatty acid synthesis, energy metabolism, and protein synthesis measured in RNA isolated from milk fat

Background

Characterising the regulation of milk component synthesis in response to macronutrient supply is critical for understanding the implications of nutritional interventions on milk production. Gene expression in mammary gland secretory cells was measured using RNA isolated from milk fat globules from 6 Holstein-Friesian cows receiving 5-d abomasal infusions of saline, essential amino acids (AA), or glucose (GG) or palm olein (LG) without (LAA) or with (HAA) essential AA, according to a 6 × 6 Latin square design. RNA was isolated from milk fat samples collected on d 5 of infusion and subjected to real-time quantitative PCR. We hypothesised that mRNA expression of genes involved in de novo milk fatty acid (FA) synthesis would be differently affected by GG and LG, and that expression of genes regulating transfer of tricarboxylic acid cycle intermediates would increase at the HAA level. We also hypothesised that the HAA level would affect genes regulating endoplasmic reticulum (ER) homeostasis but would not affect genes related to the mechanistic target of rapamycin complex 1 (mTORC1) or the integrated stress response (ISR) network.

Results

Infusion of GG did not affect de novo milk FA yield but decreased expression of FA synthase (FASN). Infusion of LG decreased de novo FA yield and tended to decrease expression of acetyl-CoA carboxylase 1 (ACC1). The HAA level increased both de novo FA yield and expression of ACC1, and tended to decrease expression of mitochondrial phosphoenolpyruvate carboxykinase (PCK2). mRNA expression of mTORC1 signaling participants was not affected by GG, LG, or AA level. Expression of the ε subunit of the ISR constituent eukaryotic translation initiation factor 2B (EIF2B5) tended to increase at the HAA level, but only in the presence of LG. X-box binding protein 1 (XBP1) mRNA was activated in response to LG and the HAA level.

Conclusions

Results show that expression of genes involved in de novo FA synthesis responded to glucogenic, lipogenic, and aminogenic substrates, whereas genes regulating intermediate flux through the tricarboxylic acid cycle were not majorly affected. Results also suggest that after 5 d of AA supplementation, milk protein synthesis is supported by enhanced ER biogenesis instead of signaling through the mTORC1 or ISR networks.

Investigation on the suitability of milk-derived primary bovine mammary epithelial cells grown on permeable membrane supports as an in vitro model for lactation

This study aimed to establish an in vitro model for lipid synthesis in primary bovine mammary epithelial cells (pbMECs) extracted from milk and cultured on Transwell permeable supports (TW culture). The suitability of these cells as a functional model for lactation was assessed by measuring κ-casein (CSN3) and diacylglycerol acyl transferase 1 (DGAT1) gene expression, the presence of intracellular lipid droplets, and the concentration of triacylglycerol in the cell lysates. The functionality of the milk-derived pbMECs cultured under lactogenic conditions, with and without oleic acid supplementation, was evaluated by comparing the cells grown on Transwell supports to cells grown on an extracellular matrix (ECM) gel (3D culture) or a plastic surface (2D culture). Furthermore, the functionality of milk-derived cells was compared to pbMECs obtained from bovine mammary tissue. Here, we show that in both tissue and milk-derived pbMECs, 3D culture offered the most suitable in vitro environment and led to increased levels of CSN3 and DGAT1 gene expression along with increased intracellular triacylglycerol content. The TW culture conditions also resulted in increased DGAT1 gene expression compared to the 2D conditions and milk-derived pbMECs cultured on TW inserts showed the highest viability compared to cells grown under 2D or 3D treatments. However, this was not observed for tissue-derived pbMECs, suggesting that TW culture may offer a beneficial environment specifically for milk-derived cells. We suggest that with further optimization of the culture conditions, TW culture may present a suitable model for the study of milk lipid synthesis in pbMECs.

Review: the cellular mechanisms underlying mammary tissue plasticity during lactation in ruminants

The mammary tissue is characterized by its capacity to adapt in response to a wide variety of changing conditions. This adaptation capacity is referred to as the plasticity of mammary tissue. In dairy ruminants, lactation is challenged by modifications that can either be induced on purpose, such as by modifying management practices, or occur involuntarily, when adverse environmental constraints arise. These modifications can elicit both immediate changes in milk yield and composition and carryover effects that persist after the end of the challenge. This review focuses on the current knowledge concerning the cellular mechanisms underlying mammary tissue plasticity. The main mechanisms contributing to this phenomenon are changes in the activity and number of mammary epithelial cells (MECs). Changes in the number of these cells result from variations in the rates of cell proliferation and death as well as changes in the rate MEC exfoliation. The number of MECs also depends on the number of resident adult mammary stem cells and their progenitors, which can regenerate the pools of the various mammary cells. Several challenges, including changes in milking frequency, changes in level of feed supply and hormonal manipulations, have been shown to modulate milk yield together with changes in mammary cell activity, turnover and exfoliation. Epigenetic changes may be an additional mechanism of adaptation. Indeed, changes in DNA methylation and reductions in milk yield have been observed during once-daily milking and during mastitis in dairy cows and may affect cell activity persistently. In contrast to what has been assumed for a long time, no carryover effect on milk yield were observed after feed supply challenges in dairy cows and modification of milking frequency in dairy goats, even though the number of mammary cells was affected. In addition, mammary tissue plasticity has been shown to be influenced by the stage of lactation, health status and genetic factors. In conclusion, the cellular mechanisms underlying mammary tissue plasticity are diverse, and the mammary tissue either does or does not show elastic properties (with no permanent deformation), in response to environmental changes.

A redefinition of the modeled responses of mammary glands to once-daily milking

Milking cows once daily is a management tool that has been implemented to improve physical and financial results of seasonal pasture-based dairy farms. The Molly cow model integrates physiology and metabolism of dairy cattle; however, milk production during short-term changes in milking frequency (e.g., 1× milking) is not well represented. The model includes a representation of variable rates of cell quiescence and death. However, the rate constants governing cell death and the return of quiescent to active cells are not affected by milking frequency. An empirical assessment of the problem was conducted, and it was hypothesized that changing the current representation of the rate of cell death in response to short-term 1× milking would more accurately represent active and quiescent cells and improve predictions of milk production. An extra senescent cell flux was added to account for cell loss during periods of 1× milking. Additional changes included a gradual decline in the rate of 1× stimulated senescence during 1× milking, and a structural change in cell cycling between active and quiescent cells during and after short-term 1× milking. Data used for parameter estimation were obtained from 5 studies where 1× milking or different feeding strategies were tested. Parameter estimates of cell loss indicated that 1× milking would affect a small proportion of quiescent cells to cause extra cell death. This added cell senescence was influenced by the length of 1× milking such that cell senescence peaked on d 1 of 1× milking and decayed from that point. The new structure in the model includes a variable rate of cell death in response to 1× milking and a gradual rate of return of quiescent cells back to the active pool in response to switching to 2× milking after short-term 1× milking. Root mean square errors, mean bias, and slope bias declined by at least 50% for predictions of energy-corrected milk yield and fat percent. The model showed quantitative agreement with production data from short-term 1× milking. The accuracy of predictions was improved and the error was reduced by implementing modifications in the model in response to changes in milking frequency.

Expression of genes related to energy metabolism and the unfolded protein response in dairy cow mammary cells is affected differently during dietary supplementation with energy from protein and fat

Secretory capacity of bovine mammary glands is enabled by a high number of secretory cells and their ability to use a range of metabolites to produce milk components. We isolated RNA from milk fat to measure expression of genes involved in energy-yielding pathways and the unfolded protein response in mammary glands of lactating cows given supplemental energy from protein (PT) and fat (FT) tested in a 2 × 2 factorial arrangement. We hypothesized that PT and FT would affect expression of genes in the branched-chain AA catabolic pathway and tricarboxylic acid (TCA) cycle based on the different energy types (aminogenic versus lipogenic) used to synthesize milk components. We also hypothesized that the response of genes related to endoplasmic reticulum (ER) homeostasis via the unfolded protein response would reflect the increase in milk production stimulated by PT and FT. Fifty-six multiparous Holstein-Friesian dairy cows were fed a basal total mixed ration (34% grass silage, 33% corn silage, 5% grass hay, and 28% concentrate on a dry matter basis) for a 28-d control period. Experimental rations were then fed for 28 d, consisting of (1) low protein, low fat (LP/LF); (2) high protein, low fat (HP/LF); (3) low protein, high fat (LP/HF); or (4) high protein and high fat (HP/HF). To obtain the high-protein (HP) and high-fat (HF) diets, intake of the basal ration was restricted and supplemented isoenergetically (net energy basis) with 2.0 kg/d rumen-protected protein (soybean + rapeseed, 50:50 mixture on dry matter basis) and 0.68 kg/d hydrogenated palm fatty acids on a dry matter basis. RNA from milk fat samples collected on d 27 of each period underwent real-time quantitative PCR. Energy from protein increased expression of BCAT1 (branched-chain amino acid transferase 1) mRNA, but only at the LF level, and tended to decrease expression of mRNA encoding the main subunit of the branched-chain keto-acid dehydrogenase complex. mRNA expression of malic enzyme, a proposed channeling route for AA though the TCA cycle, was decreased by PT, but only at the LF level. Expression of genes associated with de novo fatty acid synthesis was not affected by PT or FT. Energy from fat had no independent effect on genes related to ER homeostasis. At the LF level, PT activated XBP1 (X-box binding protein 1) mRNA. At the HF level, PT increased mRNA expression of the gene encoding GADD34 (growth arrest and DNA damage-inducible 34). These findings support our hypothesis that mammary cells use aminogenic and lipogenic precursors differently for milk component production when dietary intervention alters AA and fatty acid supply. They also suggest that mammary cells respond to increased AA supply through mechanisms of ER homeostasis, dependent on the presence of FT.

Milk-derived mammary epithelial cells as non-invasive source to define stage-specific abundance of milk protein and fat synthesis transcripts in native Sahiwal cows and Murrah buffaloes

The molecular physiology of milk production of two important dairy species; Sahiwal cows (Bos indicus) and Murrah buffaloes (Bubalus bubalis) are not fully understood due to constraints in obtaining mammary tissue samples because of sacred and ethical reasons. The present study suggests the use of milk-derived mammary epithelial cells (MECs) as a non-invasive method to understand molecular aspects of lactation biology in dairy animals. A total of 76 MECs were collected from five different lactation periods viz. colostrum (0-2), early (5-20), peak (30-50), mid (90-140) and late lactation (> 215 days) stages from Sahiwal cows and Murrah buffaloes to study the transcription kinetics of milk protein, fat synthesis, and their regulatory genes. Significant changes were observed in milk composition of both dairy species with lactation stages. High mRNA abundance of all milk protein and fat synthesis genes was observed in MECs of Murrah buffaloes as compared to Sahiwal cows. The mRNA abundance of caseins (CSN1S1, CSN1S2, CSN2, and CSN3) and whey protein (LALBA, LF) were higher in early lactation stage. Similarly, the expression of milk fat synthesis genes (SCD, BTN1A1, ACACA, GPAM, FAPB3, FASN) was also high in early lactation stage. The relative abundance of 4 regulatory genes (JAK2, STAT5, SREBF1 and EIF4BP41) remained high during early lactation indicating their regulatory roles in lactogenesis process. Overall, results suggested a significant effect of lactation stages on milk composition and transcription abundance of milk protein and fat synthesis genes. The present study establishes the fact that milk-derived MECs could be utilized as a valuable source to understand mammary gland functioning of native cows and buffaloes.

Comparative transcriptome analysis of mammary epithelial cells at different stages of lactation reveals wide differences in gene expression and pathways regulating milk synthesis between Jersey and Kashmiri cattle

Jersey and Kashmiri cattle are important dairy breeds that contribute significantly to the total milk production of the Indian northern state of Jammu and Kashmir. The Kashmiri cattle germplasm has been extensively diluted through crossbreeding with Jersey cattle with the goal of enhancing its milk production ability. However, crossbred animals are prone to diseases resulting to unsustainable milk production. This study aimed to provide a comprehensive transcriptome profile of mammary gland epithelial cells at different stages of lactation and to find key differences in genes and pathways regulating milk traits between Jersey and Kashmiri cattle. Mammary epithelial cells (MEC) isolated from milk obtained from six lactating cows (three Jersey and three Kashmiri cattle) on day 15 (D15), D90 and D250 in milk, representing early, mid and late lactation, respectively were used. RNA isolated from MEC was subjected to next-generation RNA sequencing and bioinformatics processing. Casein and whey protein genes were found to be highly expressed throughout the lactation stages in both breeds. Largest differences in differentially expressed genes (DEG) were between D15 vs D90 (1,805 genes) in Kashmiri cattle and, D15 vs D250 (3,392 genes) in Jersey cattle. A total of 1,103, 1,356 and 1,397 genes were differentially expressed between Kashmiri and Jersey cattle on D15, D90 and D250, respectively. Antioxidant genes like RPLPO and RPS28 were highly expressed in Kashmiri cattle. Differentially expressed genes in both Kashmiri and Jersey were enriched for multicellular organismal process, receptor activity, catalytic activity, signal transducer activity, macromolecular complex and developmental process gene ontology terms. Whereas, biological regulation, endopeptidase activity and response to stimulus were enriched in Kashmiri cattle and, reproduction and immune system process were enriched in Jersey cattle. Most of the pathways responsible for regulation of milk production like JAK-STAT, p38 MAPK pathway, PI3 kinase pathway were enriched by DEG in Jersey cattle only. Although Kashmiri has poor milk production efficiency, the present study suggests possible physicochemical and antioxidant properties of Kashmiri cattle milk that needs to be further explored.

Milk yield loss in response to feed restriction is associated with mammary epithelial cell exfoliation in dairy cows

In dairy cows, feed restriction is known to decrease milk yield by reducing the number of mammary epithelial cells (MEC) in the udder through a shift in the MEC proliferation-apoptosis balance, by reducing the metabolic activity of MEC, or both. The exfoliation of MEC from the mammary epithelium into milk is another process that may participate in regulating the number of MEC during feed restriction. The aim of the present study was to clarify the mechanisms that underlie the milk yield loss induced by feed restriction. Nineteen Holstein dairy cows producing 40.0 ± 0.7 kg/d at 77 ± 5 d in milk were divided into a control group (n = 9) and a feed-restricted group (n = 10). Ad libitum dry matter intake (DMI) was recorded during a pre-experimental period of 2 wk. For 29 d (period 1), cows were fed either 100 (control) or 80% (feed-restricted) of their ad libitum DMI measured during the pre-experimental period. Then, all cows were fed ad libitum for 35 d (period 2). Milk production and DMI were recorded daily. Blood and milk samples were collected once during the pre-experimental period; on d 5, 9, and 27 of period 1; and on d 5, 9, and 30 of period 2. Mammary epithelial cells were purified from milk using an immunomagnetic method to determine the rate of MEC exfoliation. Mammary tissue samples were collected by biopsy at the end of each period to analyze the rates of cell proliferation and apoptosis and the expression of genes involved in synthesizing constituents of milk. Feed restriction decreased milk yield by 3 kg/d but had no effect on rates of proliferation and apoptosis in the mammary tissue or on the expression of genes involved in milk synthesis. The daily MEC exfoliation rate was 65% greater in feed-restricted cows than in control cows. These effects in feed-restricted cows were associated with reduced insulin-like growth factor-1 and cortisol plasma concentrations. When all cows returned to ad libitum feeding, no significant difference on milk yield or MEC exfoliation rate was observed between feed-restricted and control cows, but refeeding increased prolactin release during milking. These results show that the exfoliation process may play a role in regulating the number of MEC in the udders of dairy cows during feed restriction without any carryover effect on their milk production.

Relative gene expression analysis of β-casein gene and its transcription regulatory genes in primary buffalo mammary epithelial cells of Surti and Jaffarabadi buffaloes

The present study was designed to estimate the relative gene expression of major genes responsible for β-casein and its transcription regulation during early lactation cycle in Surti and Jaffarabadi buffaloes. Ten buffaloes of each breed maintained at Livestock Research Station, Navsari and Cattle Breeding Farm, Junagadh, respectively were selected for the study. The RNA was extracted from noninvasively isolated primary buffalo mammary epithelial cells (pBMEC) obtained using antibody mediated magnetic separation method from milk samples collected at day 15 and 60 postpartum (pp). Primers used for amplification of β-casein gene (CSN2) and its transcription regulatory genes were bovine specific. The mean relative expressions of C/EBPβ, RUNX2 and STAT5A genes were significantly higher in Jaffarabadi buffaloes as compared to Surti buffaloes at day 15 pp. However, between breed differences in the mean relative expressions of C/EBPβ, RUNX2 and STAT5A genes were not observed at 60 days pp. The relative expressions of CSN2 and YY1 genes did not differ significantly within or between breeds. The mean relative expression of KRT8 gene was almost comparable among all the groups under present study. Thus, only β- casein transcription regulatory genes C/EBPβ, RUNX2 and STAT5A amongst all studied genes showed significant between breed variability at day 15 pp, however this variability too got subsided as lactation stage advanced to day 60 pp.

Mammary epithelium disruption and mammary epithelial cell exfoliation during milking in dairy cows

The presence of mammary epithelial cells (MEC) in the milk of ruminants indicates that some MEC are shed from the mammary epithelium; however, the mechanisms that regulate the MEC exfoliation process are not known. Through the release of oxytocin, prolactin, and cortisol and through oxytocin-induced mechanical forces on the mammary epithelium, milking could participate in regulating the MEC exfoliation process. The aims of the present study were to determine the rate of MEC exfoliation throughout milking and to investigate its relationship to mammary epithelium integrity and milking-induced hormone release. Milk samples from 9 Holstein dairy cows producing 40.6 ± 1.36 kg of milk/d were collected at the beginning (after 1 and 2 min), in the middle, and at the end of milking. Milk MEC were purified using an immunomagnetic method. Blood samples were collected before, during, and after milking, and the oxytocin, prolactin, and cortisol concentrations in the samples were measured. Tight junction opening was assessed by plasma lactose concentration and the Na⁺:K⁺ ratio in milk. The somatic cell count in milk varied during the course of milking; it decreased at the beginning of milking and then increased, reaching the highest values at the end of milking. Exfoliated MEC were present in all milk samples collected. The presence of MEC in the milk sample collected during min 1 of milking, likely corresponding to the cisternal milk fraction, suggests that MEC were exfoliated between milkings. The observed increase in the Na⁺:K⁺ ratio in milk and in the plasma concentration of lactose indicated that disruption of mammary epithelium integrity occurred during milking. The MEC exfoliation rate at milking was not correlated with the variables describing milking-induced prolactin release but was negatively correlated with cortisol release, suggesting that cortisol may play a role in limiting exfoliation. In conclusion, milking induced a disruption of the mammary epithelial barrier. Mammary epithelial cells may be continuously exfoliated between milkings or exfoliated during milking as a consequence of the oxytocin-induced mechanical forces and the disruption of mammary epithelium integrity.

Establishment of a 3D cell culture model of primary bovine mammary epithelial cells extracted from fresh milk

For the investigation of molecular processes underlying diseases of the bovine mammary gland, primary bovine mammary epithelial cells (pbMEC) are used. They are known to contribute to the innate immune system of the bovine mammary gland. The functionality of pbMEC depends on the maintenance of in vivo characteristics. So far, the optimization of pbMEC culture conditions was intended in a variety of experiments. For this purpose, most of the studies used stable cell lines or primary cells obtained from udder biopsies of slaughtered animals. By contrast, within our study, pbMEC of healthy and first lactating Brown Swiss cows were non-invasively isolated from fresh milk. The non-invasively isolated pbMEC were cultivated on the extracellular matrix-like scaffold Matrigel®_. Further, they were challenged with different compositions of proliferation media, containing lactogenic hormones and/or the essential amino acid L-lysine. Changes in expression levels of genes coding for milk proteins and for components of the janus kinase/signal transducers and activators of transcription (JAK-STAT) and mTOR pathways were analyzed by RT-qPCR. The secreted proteins were analyzed by LC-MS/MS measurements. We showed for the first time the establishment of a physiologically functional 3D cell culture model of pbMEC isolated from fresh milk. This represents a primary cell culture model system, based on non-invasive cell collection, that can be used to unravel physiological processes in an unbiased manner.

Relative gene expression of fatty acid synthesis genes at 60 days postpartum in bovine mammary epithelial cells of Surti and Jafarabadi buffaloes

Aim:

Aim of the study was to study the relative gene expression of genes associated with fatty acid synthesis at 60 days postpartum (pp) in bovine mammary epithelial cells (MECs) of Surti and Jafarabadi buffaloes.

Materials and Methods:

A total of 10 healthy Surti and Jafarabadi buffaloes of each breed were selected at random from Livestock Research Station, Navsari and Cattle Breeding Farm, Junagadh, Gujarat, respectively, for this study. Milk sample was collected from each selected buffalo at day 60 pp from these two breeds to study relative gene expression of major milk fat genes using non-invasive approach of obtaining primary bovine MECs (pBMEC) from milk samples.

Results:

In this study overall, the relative expression of the six major milk lipogenic genes butyrophilin subfamily 1 member A1 (BTN1A1), stearoyl-CoA desaturase (SCD), lipoprotein lipase (LPL), glycerol-3-phosphate acyltransferase mitochondrial (GPAM), acetyl-coenzyme A carboxylase alpha (ACACA), and lipin (LPIN) did not show changes in expression patterns at 60^th day of lactation in both Surti and Jafarabadi buffaloes.

Conclusion:

The pBMEC can be successfully recovered from 1500 ml of milk of Surti and Jafarabadi buffaloes using antibody-mediated magnetic bead separation and can be further used for recovering RNA for down step quantification of major milk lipogenic gene expression. The relative expression of the six major milk lipogenic genes BTN1A1, SCD, LPL, GPAM, ACACA, and LPIN did not show changes in expression patterns in both Surti and Jafarabadi buffaloes, suggesting expression levels of lipogenic genes are maintained almost uniform till peak lactation without any significant difference.

The Use of "Omics" in Lactation Research in Dairy Cows

“Omics” is the application of genomics, transcriptomics, proteomics, and metabolomics in biological research. Over the years, tremendous amounts of biological information has been gathered regarding the changes in gene, mRNA and protein expressions as well as metabolites in different physiological conditions and regulations, which has greatly advanced our understanding of the regulation of many physiological and pathophysiological processes. The aim of this review is to comprehensively describe the advances in our knowledge regarding lactation mainly in dairy cows that were obtained from the “omics” studies. The “omics” technologies have continuously been preferred as the technical tools in lactation research aiming to develop new nutritional, genetic, and management strategies to improve milk production and milk quality in dairy cows.

Combinação de butafosfan e cianocobalamina no metabolismo da glicose em vacas leiteiras após o parto

RESUMO A hipótese deste estudo é de que o uso da combinação de butafosfan e cianocobalamina pode melhorar a resistência periférica à insulina, aumentar a quantidade de glicose disponível para a glândula mamária e a produção de leite. Assim, o objetivo foi investigar os efeitos combinados de butafosfan e cianocobalamina sobre o metabolismo da glicose em vacas leiteiras no período pós-parto. Vinte e uma vacas leiteiras foram divididas em dois grupos: grupo controle (CON, n= 11), que recebeu cinco aplicações de solução salina (20mL / animal 0,9% NaCl), e grupo Catosal(r) (ABC, n= 10), que recebeu cinco aplicações de 20mL de uma solução contendo as substâncias butafosfan e cianocobalamina (B12 Catosal(r), 100mg da substância butafosfan e 50µg de cianocobalamina por mL). As aplicações foram realizadas por via intramuscular, nos dias sete, 12, 17, 22 e 27 pós-parto. As amostras de sangue foram coletadas para a avaliação das concentrações plasmáticas de fósforo, glicose, ácidos graxos não esterificados (AGNE), albumina, aspartato aminotransferase (AST) e creatina quinase (CK). Nos dias oito e 28 pós-parto, os animais foram pesados e submetidos aos testes de tolerância à glicose e à insulina. O tratamento promoveu perda de peso (ABC 40,4kg, CON 10,73kg, P<0,05) e aumento da AST (ABC 62,92 ±3,31U/L, CON 53,11±3,49 U / L, P<0,05) e dos níveis de CK (ABC 134,09± 19,08U / L, CON 79,43 ± 18,27U / L). Os grupos não diferiram quanto ao metabolismo (área sob a curva) da glicose nos dias oito e 28, porém os animais tratados tiveram um aumento na glicemia (P<0,05) no dia 28 pós-parto (97,54 ± 8,54mg / dL), após a administração de insulina, em comparação ao dia oito (83,01 ± 8,54mg / dL). Assim, pode-se concluir que a combinação de butafosfan e cianocobalamina melhora a adaptação do metabolismo da glicose em vacas leiteiras no início da lactação.

The effect of long term under- and overfeeding on the expression of genes related to glucose metabolism in the mammary tissue of goats

The glucose metabolism in the mammary tissue (MT) is controlled by several genes whose nutritional regulation is poorly documented. In this study, the effect of long-term under- and overfeeding on the expression of glucose transporter 1 (GLUT1), glucose transporter 3 (GLUT3), sodium glucose contransporter 1 (SGLT1), two isoforms of β- (1, 4) galactosyltransferase [β- (1, 4) GAT1 and β- (1, 4) GAT3], and α-lactalbumin (LALBA), related to glucose metabolism in goat MT, was examined by using real-time RT-PCR. Twenty- four lactating goats were divided into three homogenous subgroups and fed the same ration in quantities covering 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements, respectively. The results showed that the feeding level did not affect the GLUT1, GLUT3 and SGLT1 genes expression in goats MT. On the contrary, a significant reduction and a trend for reduction on mRNA of β- (1, 4) GAT1 and on β- (1, 4) GAT3, respectively, in the MT of underfed goats, compared with the overfed ones, was observed. Moreover, a significant decrease in the LALBA mRNA accumulation in the MT of underfed goats compared with the overfed was found. In conclusion, the MT of goats, unlike cows, adapt to changes in glucose or energy supply from different levels of feeding by changing the utilisation of glucose for the synthesis of lactose.

Advances in research on cis-9, trans-11 conjugated linoleic acid: a major functional conjugated linoleic acid isomer

Conjugated linoleic acid (CLA) consists of a group of positional and geometric conjugated isomers of linoleic acid. Since the identification of CLA as a factor that can inhibit mutagenesis and carcinogenesis, thousands of studies have been conducted in the last several decades. Among the many isomers discovered, cis-9, trans-11 CLA is the most intensively studied because of its multiple, isomer-specific effects in humans and animals. This paper provides an overview of the available data on cis-9, trans-11 CLA, including its isomer-specific effects, biosynthesis, in vivo/in vitro research models, quantification, and the factors influencing its content in ruminant products.

The effect of long-term under- and overfeeding on the expression of six major milk proteins' genes in the mammary tissue of goats

Milk protein synthesis in the mammary gland involves expression of six major milk proteins' genes whose nutritional regulation remains poorly defined. In this study, the effect of long-term under- and overfeeding on the expression of as1-casein: CSN1S1, as2-casein: CSN1S2, β-casein: CSN2, κ-casein: CSN3, α-lactalbumin: LALBA and β-lactoglobulin: BLG gene in goat mammary tissue (MT) was examined. Twenty-four lactating dairy goat, at 90-98 days in milk, were divided into three homogenous subgroups and fed the same ration, for 60 days, in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant decrease in mRNA of CSN1S2, CSN2, CSN3 and LALBA genes in the MT of underfed goats compared with the overfed and on the CSN1S1 and BLG gene expressions in the MT of underfed goats compared with the respective control and overfed. CSN2 was the most abundant transcript in goat MT relative to the other milk proteins' genes. Significantly positive correlations were observed between the mRNA levels of caseins' and BLG genes with the milk yield. Moreover, a significant correlation was found between the mRNA levels of CSN1S2 with the milk protein, lactose content and lactose yield and also between the LALBA gene expression with the lactose content and lactose yield respectively. In conclusion, the feeding level and consequently the nutrients availability affected the milk lactose content, protein and lactose yield as well as the milk volume by altering the CSN1S1, CSN1S2, CSN2, CSN3, LALBA and BLG gene expression involved in their metabolic pathways.

Mammary epithelial cells isolated from milk are a valuable, non-invasive source of mammary transcripts

Milk is produced in the udder by mammary epithelial cells (MEC). Milk contains MEC, which are gradually exfoliated from the epithelium during lactation. Isolation of MEC from milk using immunomagnetic separation may be a useful non-invasive method to investigate transcriptional regulations in ruminants' udder. This review aims to describe the process of isolating MEC from milk, to provide an overview on the studies that use this method to analyze gene expression by qRT PCR and to evaluate the validity of this method by analyzing and comparing the results between studies. In several goat and cow studies, consistent reductions in alpha-lactalbumin mRNA levels during once-daily milking (ODM) and in SLC2A1 mRNA level during feed restriction are observed. The effect of ODM on alpha-lactalbumin mRNA level was similarly observed in milk isolated MEC and mammary biopsy. Moreover, we and others showed decreasing alpha-lactalbumin and increasing BAX mRNA levels with advanced stages of lactation in dairy cows and buffalo. The relevance of using the milk-isolated MEC method to analyze mammary gene expression is proven, as the transcript variations were also consistent with milk yield and composition variations under the effect of different factors such as prolactin inhibition or photoperiod. However, the RNA from milk-isolated MEC is particularly sensitive to degradation. This could explain the differences obtained between milk-isolated MEC and mammary biopsy in two studies where gene expression was compared using qRT-PCR or RNA Sequencing analyses. As a conclusion, when the RNA quality is conserved, MEC isolated from milk are a valuable, non-invasive source of mammary mRNA to study various factors that impact milk yield and composition (ODM, feeding level, endocrine status, photoperiod modulation, and stage of lactation).

Metabolic Disorders in the Transition Period Indicate that the Dairy Cows' Ability to Adapt is Overstressed

Simple Summary

Metabolic disorders are a key problem in the transition period of dairy cows and often appear before the onset of further health problems. Problems derive from difficulties animals have to adapt to large variations and disturbances occurring both outside and inside the organism. A lack of success in solving these issues may be due to predominant approaches in farm management and agricultural science, dealing with such disorders as merely negative side effects. Instead, a successful adaptation of animals to their living conditions should be seen as an important end in itself. Both farm management and agricultural sciences should support animals in their ability to cope with nutritional and metabolic challenges by employing a functional and result-driven approach.

Abstract

Metabolic disorders are a key problem in the transition period of dairy cows and often appear before the onset of further health problems. They mainly derive from difficulties the animals have in adapting to changes and disturbances occurring both outside and inside the organisms and due to varying gaps between nutrient supply and demand. Adaptation is a functional and target-oriented process involving the whole organism and thus cannot be narrowed down to single factors. Most problems which challenge the organisms can be solved in a number of different ways. To understand the mechanisms of adaptation, the interconnectedness of variables and the nutrient flow within a metabolic network need to be considered. Metabolic disorders indicate an overstressed ability to balance input, partitioning and output variables. Dairy cows will more easily succeed in adapting and in avoiding dysfunctional processes in the transition period when the gap between nutrient and energy demands and their supply is restricted. Dairy farms vary widely in relation to the living conditions of the animals. The complexity of nutritional and metabolic processes and their large variations on various scales contradict any attempts to predict the outcome of animals’ adaptation in a farm specific situation. Any attempts to reduce the prevalence of metabolic disorders and associated production diseases should rely on continuous and comprehensive monitoring with appropriate indicators on the farm level. Furthermore, low levels of disorders and diseases should be seen as a further significant goal which carries weight in addition to productivity goals. In the long run, low disease levels can only be expected when farmers realize that they can gain a competitive advantage over competitors with higher levels of disease.

The effect of long term under- and over-feeding on the expression of six major milk protein genes in the mammary tissue of sheep

Milk protein synthesis in the mammary gland involves expression of six major milk protein genes whose nutritional regulation remains poorly defined. In this study, the effect of long term under- and over-feeding on the expression of αs1-casein: CSN1S1, αs2-casein: CSN1S2, β-casein: CSN2, κ-casein: CSN3, α-lactalbumin: LALBA and β-lactoglobulin: BLG gene in sheep mammary tissue (MT) was examined. Twenty-four lactating dairy sheep, at 90-98 d in milk, were divided into three groups and fed the same ration, for 60 d, in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction on mRNA of CSN1S1, CSN1S2, CSN2 and BLG gene in the MT of underfed sheep compared with the overfed ones and a significant reduction in CSN3 and LALBA gene expression compared with the respective control animals. Significant positive correlations were observed between the mRNA levels of milk proteins' genes with the milk protein yield and milk yield respectively. In conclusion, the feeding level and consequently the nutrients availability, affected the milk protein yield and milk volume by altering the CSN1S1, CSN1S2, CSN2, CSN3, LALBA and BLG gene expression involved in their metabolic pathways.

Proteomic Analysis Reveals PGAM1 Altering cis-9, trans-11 Conjugated Linoleic Acid Synthesis in Bovine Mammary Gland

cis-9, trans-11 Conjugated linoleic acid (CLA) is one of the most extensively studied CLA isomers due to its multiple isomer-specific effects. However, the molecular mechanisms of cis-9,trans-11 CLA synthesis in ruminant mammary gland are still not clearly understood. This process may be mediated, to a certain extent, by trans-11 C18:1 regulated by stearoyl-CoA desaturase-1 (SCD1) and/or its syntrophic proteins. This study aimed to investigate the effects of TVA on SCD1-mediated cis-9,trans-11 CLA synthesis in MAC-T cells and its potential molecular mechanism. Results showed that trans-11 C18:1 was continually taken up and converted into cis-9,trans-11 CLA in MAC-T cells during the 4-h incubation of 50 μM trans-11 C18:1. SCD1 protein expression increased more than twofold at 2 h (P < 0.01) and 2.5 h (P < 0.05) before decreasing to less than half of the normal level at 4 h (P < 0.05). One up-regulated (RAS guanyl releasing protein 4 isoform 1 [RASGRP4]) and six down-regulated proteins (glucosamine-6-phosphate deaminase 1 [GNPDA1], triosephosphate isomerase [TPI1], phosphoglycerate mutase 1 [PGAM1], heat shock protein beta-1 [HSPB1], annexin A3 [ANXA3], thiopurine S-methyltransferase [TPMT]) were found in MAC-T cells treated with trans-11 C18:1. Of these seven identified proteins, the presence of GNPDA1 and PGAM1 was verified in several models. More trans-11 C18:1 was taken up after PGAM1 knockdown by small interfering RNA (siRNA). In conclusion, our data suggested that PGAM1 may have a negative relationship with SCD1 and seemed to be involved in cis-9, trans-11 CLA synthesis by facilitating the absorption of trans-11 C18:1 in the bovine mammary gland.

Maternal perinatal undernutrition modifies lactose and serotranferrin in milk: relevance to the programming of metabolic diseases?

A close link between intrauterine growth restriction and development of chronic adult diseases such as obesity, diabetes, and hypertension has been established both in humans and animals. Modification of growth velocity during the early postnatal period (i.e., lactation) may also sensitize to the development of metabolic syndrome in adulthood. This suggests that milk composition may have long-lasting programming/deprogramming metabolic effects in the offspring. We therefore assess the effects of maternal perinatal denutrition on breast milk composition in a food-restricted 50% (FR50) rat model. Monosaccharides and fatty acids were characterized by gas chromatography, and proteins were profiled by surface-enhanced laser desorption/ionization-time-of-flight analysis in milk samples from FR50 and control rat dams. Milk analysis of FR50 rats demonstrated that maternal undernutrition decreases lactose concentration and modulates lipid profile at postnatal day 10 by increasing the unsaturated fatty acids/saturated fatty acids and diminishes serotransferrin levels at postnatal day 21. Our data indicate that maternal perinatal undernutrition modifies milk composition both quantitatively and qualitatively. These modifications by maternal nutrition open new perspectives to identify molecules that could be used in artificial milk to protect from the subsequent development of metabolic diseases.

The effect of long term under- and over-feeding on the expression of genes related to glucose metabolism in mammary tissue of sheep

Glucose utilisation for lactose synthesis in the mammary gland involves expression of a large number of genes whose nutritional regulation remains poorly defined. In this study, the effect of long term under- and over-feeding on the expression of genes [glucose transporter 1: GLUT1, glucose transporter 3: GLUT3, Sodium glucose contransporter 1: SGLT1, two isoforms of β- (1,4) galactosyltransferase: β- (1,4) GAT1, β- (1,4) GAT3 and α-lactalbumin: LALBA] related to glucose metabolism in sheep mammary tissue (MT) was examined. Twenty-four lactating dairy sheep were divided into three homogenous sub-groups and fed the same ration in quantities which met 70% (underfeeding), 100% (control) and 130% (overfeeding) of their energy and crude protein requirements. The results showed a significant reduction on mRNA of GLUT1 and LALBA gene in the MT of underfed sheep, compared with the respective controls and overfed and a significant reduction on mRNA level of SGLT1 and β- (1,4) GAT1 in the MT of underfed sheep, compared with the overfed ones. A significant increase in the GLUT3 mRNA accumulation in the MT of both under- and over- fed sheep was found. Additionally, a trend of reduction on β- (1,4) GAT3 mRNA level in the MT of the underfed sheep, compared with the overfed, was observed. A close positive relationship was obtained between the mRNA transcripts accumulation of GLUT1, SGLT1, β- (1,4) GAT1 and LALBA gene with the milk lactose content and milk lactose yield respectively. In conclusion, feeding level and consequently nutrient availability, may affect glucose uptake and utilisation in sheep MT by altering the GLUT1, GLUT3, SGLT1, β- (1,4) GAT1 and LALBA gene expression involved in their metabolic pathways.

Expression profiling of glucose transporter 1 (GLUT1) and apoptotic genes (BAX and BCL2) in milk enriched mammary epithelial cells (MEC) in riverine buffalo during lactation

Lactation is an important physiological process in dairy animals. During lactation, up to 85% of the body glucose is directed toward the mammary glands for milk synthesis. Studies related to lactation physiology are generally carried out on mammary biopsies, which may adversely affect animal health. In the present study, milk enriched MEC were used to study the expression pattern of GLUT1 and apoptotic genes (BAX and BCL2) across different stages of lactation in riverine buffalo in relation to milk yield. MEC were enriched from milk using cytokeratin-8 antibodies coated magnetic beads. Total RNA isolated from enriched MEC showed significant correlation (r(2) = 0.92 ± 0.02) with the milk yield at different stages of lactation. GLUT1 expression pattern correlated with the milk yield as highest GLUT1 expression (4.68 ± 0.79) was observed during peak-lactation (90 days post-parturition), whereas low GLUT1 expression (1.01 ± 0.1, 15 d; 0.71 ± 0.03, 30 d) was observed during early lactation. The BAX/BCL2 ratio was high (1.02 ± 0.2, 15 d; 0.94 ± 0.06, 30 d) during the early phase of lactation, indicating high rate of apoptosis, whereas low BAX/BCL2 ratio (0.25 ± 0.03, 60 d; 0.42 ± 0.04, 90 d) was observed during mid-lactation coinciding with the increase in RNA concentration and milk yield. Highest BAX/BCL2 ratio (1.41 ± 0.3, 120 d; 4.02 ± 0.6, 240 d) was observed during late lactation i.e., 240 days, which was also reflected as decline in milk yield and RNA concentration. Also, BAX/BCL2 ratio in milk enriched MEC was in accordance with RNA concentration in MEC and milk yield at different phases of lactation. Our study showed that expression pattern of genes under study (GLUT1, BAX, and BCL2) in milk enriched MEC correlated well with important physiological properties such as milk yield in buffalo.