Major advances associated with hormone and growth factor regulation of mammary growth and lactation in dairy cows

Transcriptome difference and potential crosstalk between liver and mammary tissue in mid-lactation primiparous dairy cows

Liver and mammary gland are among the most important organs during lactation in dairy cows. With the purpose of understanding both the different and the complementary roles and the crosstalk of those two organs during lactation, a transcriptome analysis was performed on liver and mammary tissues of 10 primiparous dairy cows in mid-lactation. The analysis was performed using a 4×44K Bovine Agilent microarray chip. The transcriptome difference between the two tissues was analyzed using SAS JMP Genomics using ANOVA with a false discovery rate correction (FDR). The analysis uncovered >9,000 genes differentially expressed (DEG) between the two tissues with a FDR<0.001. The functional analysis of the DEG uncovered a larger metabolic (especially related to lipid) and inflammatory response capacity in liver compared with mammary tissue while the mammary tissue had a larger protein synthesis and secretion, proliferation/differentiation, signaling, and innate immune system capacity compared with the liver. A plethora of endogenous compounds, cytokines, and transcription factors were estimated to control the DEG between the two tissues. Compared with mammary tissue, the liver transcriptome appeared to be under control of a large array of ligand-dependent nuclear receptors and, among endogenous chemical, fatty acids and bacteria-derived compounds. Compared with liver, the transcriptome of the mammary tissue was potentially under control of a large number of growth factors and miRNA. The in silico crosstalk analysis between the two tissues revealed an overall large communication with a reciprocal control of lipid metabolism, innate immune system adaptation, and proliferation/differentiation. In summary the transcriptome analysis confirmed prior known differences between liver and mammary tissue, especially considering the indication of a larger metabolic activity in liver compared with the mammary tissue and the larger protein synthesis, communication, and proliferative capacity in mammary tissue compared with the liver. Relatively novel is the indication by the data that the transcriptome of the liver is highly regulated by dietary and bacteria-related compounds while the mammary transcriptome is more under control of hormones, growth factors, and miRNA. A large crosstalk between the two tissues with a reciprocal control of metabolism and innate immune-adaptation was indicated by the network analysis that allowed uncovering previously unknown crosstalk between liver and mammary tissue for several signaling molecules.

Identification of novel candidate genes for the inverted teat defect in sows using a genome-wide marker panel

The number of functional teats is an important selection criterion in pig breeding. Inherited defects of the udder, such as the inverted teat, do have a considerable negative impact on the nursing ability of the sow. To investigate the genetic background of this defect and the number of functional teats in Swedish maternal lines, samples from 230 Yorkshire pigs were selected for genotyping using the PorcineSNP60K BeadChip (Illumina Inc.), each pig with at least one inverted teat was matched with one non-affected pig (fullsib or pairs with matching herd and gender). A genome-wide association study on these 230 pigs was performed using the two-step approach implemented in GenABEL using 46,652 single nucleotide polymorphisms across all autosomes and the X chromosome. A number of significant regions were identified for the inverted teat defect on chromosomes 2, 10, and 18. Many of the regions associated with the number of functional teats were located in the same or close regions, except two associated markers on the X chromosome and one on chromosome 3. We identified some of the regions on chromosomes previously reported in one linkage and one gene expression study. We conclude, despite being able to suggest new candidate genes, that further studies are needed to better understand the biologic background of the teat development. Despite the in-depth comparison of identified regions for the inverted teat defect done here, more studies are required to allow a clear identification of genetic regions relevant for this defect across many pig populations.

Effects of Feeding Milk Replacer Ad Libitum or in Restricted Amounts for the First Five Weeks of Life on the Growth, Metabolic Adaptation, and Immune Status of Newborn Calves

The pre-weaning period is critical for calf health and growth, and intensive milk feeding programs may assist postnatal development by improving body growth and organ maturation. The aim of the present work was to study the effects of ad libitum milk replacer (MR) feeding on the growth, metabolic adaptation, health, and immune status of newborn calves. Twenty-eight newborn Holstein and Holstein x Charolais crossbred calves were fed ad libitum (ADLIB) or in restricted amounts (6 liters per day; RES) during the first five weeks of life. The MR intake in the ADLIB treatment was gradually reduced at weeks 6 and 7, and all calves then received 6 liters of MR per day until day 60. Blood samples were collected to measure the plasma concentrations of metabolites, insulin, insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP), immunoglobulins, and acute phase proteins. The expression of mRNA associated with both the somatotropic axis and gluconeogenic enzymes was measured in the liver on day 60. Intensive feeding improved MR intake and growth in ADLIB without influencing concentrate intake. Carcass weight, perirenal fat, and muscle mass were greater in ADLIB. Plasma concentrations of glucose, triglycerides, insulin, and IGF-I were greater, whereas plasma concentrations of β-hydroxybutyrate, total protein, albumin, urea, IGFBP-2 and -4, and fibrinogen were lower at distinct time points in ADLIB. The hepatic mRNA expression of cytosolic phosphoenolpyruvate carboxykinase was greater in ADLIB. Most metabolic and endocrine differences occurred during the MR feeding period, but a slightly greater concentrate intake was associated with increased plasma IGF-I and insulin at the end of the study. The immune and health status of the calves were not affected by MR feeding. However, increased plasma fibrinogen in the RES group suggested differences in the acute phase response.

The role of rumen-protected choline in hepatic function and performance of transition dairy cows

High-producing dairy cows enter a period of negative energy balance during the first weeks of lactation. Energy intake is usually sufficient to cover the increase in energy requirements for fetal growth during the period before calving, but meeting the demand for energy is often difficult during the early stages of lactation. A catabolic state predominates during the transition period, leading to the mobilisation of energy reserves (NEFA and amino acids) that are utilised mainly by the liver and muscle. Increased uptake of mobilised NEFA by the liver, combined with the limited capacity of hepatocytes to either oxidise fatty acids for energy or to incorporate esterified fatty acids into VLDL results in fatty liver syndrome and ketosis. This metabolic disturbance can affect the general health, and it causes economic losses. Different nutritional strategies have been used to restrict negative effects associated with the energy challenge in transition cows. The provision of choline in the form of rumen-protected choline (RPC) can potentially improve liver function by increasing VLDL exportation from the liver. RPC increases gene expression of microsomal TAG transfer protein and APOB100 that are required for VLDL synthesis and secretion. Studies with RPC have looked at gene expression, metabolic hormones, metabolite profiles, milk production and postpartum reproduction. A reduction in liver fat and enhanced milk production has been observed with RPC supplementation. However, the effects of RPC on health and reproduction are equivocal, which could reflect the lack of sufficient dose–response studies.

Anti-Inflammatory and Antimicrobial Effects of Estradiol in Bovine Mammary Epithelial Cells during Staphylococcus aureus Internalization

17β-Estradiol (E2), the predominant sexual hormone in females, is associated with the modulation of the innate immune response (IIR), and changes in its levels at parturition are related to intramammary infections, such as mastitis. In bovine mammary epithelial cells (bMECs), E2 regulates differentiation and proliferation, but its immunomodulatory functions have not been explored. Staphylococcus aureus is the predominant pathogen causing mastitis, which can persist intracellularly in bMECs. The aim of this work was to analyze whether E2 modulates the IIR of bMECs during S. aureus internalization. bMECs treated with E2 (50 pg/mL, 24 h) reduced bacteria internalization (~50%). The host receptors α5β1 and TLR2 do not participate in this reduction. However, E2 activates ERα and modulates the IIR reducing the S. aureus induced-mRNA expression of TNF-α (~50%) and IL-1β (90%). E2 also decreased the secretion of these cytokines as well as IL-6 production; however, in infected bMECs, E2 induced the secretion of IL-1β. Furthermore, E2 upregulates the expression of the antimicrobial peptides DEFB1, BNBD5, and psoriasin S100A7 (~5-, 3-, and 6-fold, resp.). In addition, E2 induced the production of antimicrobial compounds in bMEC culture medium, which, together with the modulation of the IIR, could be related to the reduction of S. aureus internalization.

Bovine lactotroph cultures for the study of prolactin synthesis functions

The aim of this study was to establish a bovine anterior pituitary-derived lactotroph (BAPDL) line that expresses prolactin (PRL) in vitro to study the mechanisms of bovine PRL synthesis and secretion. Immunohistochemistry assay of PRL in the newborn calves' anterior pituitary glands showed that most lactotrophs were located within the superior border of the lateral wings of the anterior pituitary. Tissues of the superior border of the lateral wings of the anterior pituitary were dispersed and cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FBS). The limiting dilution method was used to establish BAPDL from single cell clone. BAPDL cells constantly expressed mRNAs for PRL and pituitary-specific transcription factor 1 (Pit-1) gene and grew steadily and rapidly in the DMEM supplemented with 10% FBS. PRL immunoreactivity was present in BAPDL at passage 20. The concentration of bovine PRL in BAPDL at passage 20 culture supernatant was decreased to below 35% compared with that in BAPDL at passage 1. The effects of human epidermal growth factor (hEGF) and dopamine (DA) on the expression and secretion of PRL in BAPDL at passage 4 were also investigated. The results are consistent with those of previous studies. Thus, it can be used successfully for studying the mechanisms of stimuli regulating PRL synthesis and release.

Lactogenic hormones regulate mammary protein synthesis in bovine mammary epithelial cells via the mTOR and JAK–STAT signal pathways

The expression of CSN3, hormone receptor, the expression of genes regulating the mTOR, JAK–STAT signal pathways, and the relative content of к-casein as well as total casein were determined in the present study to explore the mechanism of the effect of lactogenic hormones on milk-protein synthesis in bovine mammary epithelial cells. The results showed that apoptosis of the cells was increased by inhibitor LY294002, while the expressions of genes encoding PKB, Rheb, PRAS40 and S6K1 in the mTOR signal pathway, JAK2, STAT5A in the JAK–STAT signal pathway, and genes encoding INSR, PRLR, NR3C1 and CSN3 were all downregulated, and the relative contents of κ-casein and total casein were decreased in the mammary epithelial cells compared with those in the control group. Comparatively, the inhibitory effects of AG-490 were more profound than those of LY294002, and the double block using both inhibitors had a greater effect than the single block. The CSN3 gene expression was downregulated and the content of milk casein was decreased by the inhibitors. In addition, the expression of the hormone receptor genes was downregulated. Our results suggest that lactogenic hormones, via their receptors in the membrane, regulated the JAK–STAT and m-TOR signal pathways, and affected cell proliferation and apoptosis, leading to changes in milk-protein synthesis.

The relationship of GH and LEP gene polymorphisms with fat-tail measurements (fat-tail dimensions) in fat-tailed Makooei breed of Iranian sheep

Background:

The present study was designed to investigate the association of GH and LEP genes’ single-nucleotide polymorphisms with fat-tail measurements (fat-tail dimensions) in Makooei sheep.

Materials and Methods:

DNA was extracted from whole blood samples collected from 100 sheep. Polymerase chain reaction (PCR) products were subjected to single-strand conformation polymorphism (SSCP) denaturation and polyacrylamide gel electrophoresis. Data were collected at the Makooei Sheep Breeding Station in Makoo (36°, 35′S and 48°, 22′E) of West Azerbaijan province. Climatically, this location has temperate summers and cold winters and receives a mean annual rainfall of about 400 mm. Ewes are raised in an annual breeding cycle starting in September. In general, the flock is managed under a semi-migratory system.

Results:

In the tested Makooei sheep population, significant statistical results were found in all traits of fat-tail measurements for GH and LEP genes. Individuals with the G4, L4 genotype of GH and LEP genes had lower tail length (rump length), fat thickness (the thick rump), and tail width (rump width) when compared to those of individuals with other genotypes (P < 0.05). In addition, the results demonstrated that individuals with the G5, L5 genotype of GH and LEP genes had superiority of tail length (rump length) and fat thickness (the thick rump) compared to those individuals with other genotypes (P < 0.05). Individuals with the G2, L2 genotype of GH and LEP genes had superiority of tail width (rump width) compared individuals with other genotypes (P < 0.05).

Conclusion:

These results confirmed potential usefulness of GH and LEP genes in marker-assisted selection programs of sheep breeding.

Differences of hormones involved in adipose metabolism and lactation between high and low producing Holstein cows during heat stress

The experiment was conducted to evaluate hormonal involvement in the adipose metabolism and lactation between high and low producing dairy cows in a hot environment. Forty Holstein healthy cows with a similar parity were used and assigned into high producing group (average production 41.44 ± 2.25 kg/d) and low producing group (average production 29.92 ± 1.02 kg/d) with 20 cows in each group. Blood samples were collected from caudal vein to determine the difference of hormones related to adipose metabolism and lactation. The highest, lowest, and average temperature humidity index (THI), recorded as 84.02, 79.35 and 81.89, respectively, indicated that cows were at the state of high heat stress. No significant differences between high and low producing groups were observed in the levels of nonestesterified fatty acid (NEFA), β-hydroxybutyrate (β-OHB), total cholesterol (TCHO), and insulin (INS) (P > 0.05). However, the very low density lipoprotein (VLDL), apolipoprotein B100 (apoB-100), high-density lipoprotein (HDL-C) and estrogen (E₂) concentrations in high producing group were significantly higher than those of low producing group (P < 0.05). No significant differences between high and low producing groups were observed in the levels of prolactin (PRL) and progesterone (PROG) (P > 0.05), whereas high producing group had a rise in the insulin-like growth factor-1 (IGF-1) level compared with low producing group (P < 0.05). These results indicated that, during summer, high and low producing dairy cows have similar levels of lipid catabolism, but high producing dairy cows have advantages in outputting hepatic triglyceride (TG).

Alterations in Hepatic FGF21, Co-Regulated Genes, and Upstream Metabolic Genes in Response to Nutrition, Ketosis and Inflammation in Peripartal Holstein Cows

In rodents, fibroblast growth factor 21 (FGF21) has emerged as a key metabolic regulator produced by liver. To gather preliminary data on the potential importance of FGF1, co-regulated genes, and upstream metabolic genes, we examined the hepatic mRNA expression in response to nutrition and inflammation in dairy cows. In experiment 1, induction of ketosis through feed restriction on d 5 postpartum upregulated FGF21, its co-receptor KLB, and PPARA but only elicited a numerical increase in serum FGF21 concentration. In experiment 2, cows in control (CON) or receiving 50 g/d of L-carnitine (C50) from -14 through 21 d had increased FGF21, PPARA, and NFIL3 on d 10 compared with d 2 postpartum. In contrast, compared with CON and C50, 100 g/d L-carnitine (C100) resulted in lower FGF21, KLB, ANGPTL4, and ARNTL expression on d 10. In experiment 3, cows were fed during the dry period either a higher-energy (OVE; 1.62 Mcal/kg DM) or lower-energy (CON; 1.34 Mcal/kg DM) diet and received 0 (OVE:N, CON:N) or 200 μg of LPS (OVE:Y, CON:Y) into the mammary gland at d 7 postpartum. For FGF21 mRNA expression in CON, the LPS challenge (CON:Y) prevented a decrease in expression between d 7 and 14 postpartum such that cows in CON:N had a 4-fold lower expression on d 14 compared with d 7. The inflammatory stimulus induced by LPS in CON:Y resulted in upregulation of PPARA on d 14 to a similar level as cows in OVE:N. In OVE:Y, expression of PPARA was lower than CON:N on d 7 and remained unchanged on d 14. On d 7, LPS led to a 4-fold greater serum FGF21 only in OVE but not in CON cows. In fact, OVE:Y reached the same serum FGF21 concentration as CON:N, suggesting a carryover effect of dietary energy level on signaling mechanisms within liver. Overall, results indicate that nutrition, ketosis, and inflammation during the peripartal period can alter hepatic FGF21, co-regulated genes, and upstream metabolic genes to various extents. The functional outcome of these changes merits further study, and in particular the mechanisms regulating transcription in response to changes in energy balance and feed intake.

Functional development of the adult ovine mammary gland--insights from gene expression profiling

Background

The mammary gland is a dynamic organ that undergoes dramatic physiological adaptations during the transition from late pregnancy to lactation. Investigation of the molecular basis of mammary development and function will provide fundamental insights into tissue remodelling as well as a better understanding of milk production and mammary disease. This is important to livestock production systems and human health.

Here we use RNA-seq to identify differences in gene expression in the ovine mammary gland between late pregnancy and lactation.

Results

Between late pregnancy (135 days of gestation ± 2.4 SD) and lactation (15 days post partum ± 1.27 SD) 13 % of genes in the sheep genome were differentially expressed in the ovine mammary gland. In late pregnancy, cell proliferation, beta-oxidation of fatty acids and translation were identified as key biological processes. During lactation, high levels of milk fat synthesis were mirrored by enrichment of genes associated with fatty acid biosynthesis, transport and lipogenesis. Protein processing in the endoplasmic reticulum was enriched during lactation, likely in support of active milk protein synthesis. Hormone and growth factor signalling and activation of signal transduction pathways, including the JAK-STAT and PPAR pathways, were also differently regulated, indicating key roles for these pathways in functional development of the ovine mammary gland. Changes in the expression of epigenetic regulators, particularly chromatin remodellers, indicate a possible role in coordinating the large-scale transcriptional changes that appear to be required to switch mammary processes from growth and development during late pregnancy to synthesis and secretion of milk during lactation.

Conclusions

Coordinated transcriptional regulation of large numbers of genes is required to switch between mammary tissue establishment during late pregnancy, and activation and maintenance of milk production during lactation. Our findings indicate the remarkable plasticity of the mammary gland, and the coordinated regulation of multiple genes and pathways to begin milk production. Genes and pathways identified by the present study may be important for managing milk production and mammary development, and may inform studies of diseases affecting the mammary gland.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1947-9) contains supplementary material, which is available to authorized users.

Genomic imprinting effects on complex traits in domesticated animal species

Monoallelically expressed genes that exert their phenotypic effect in a parent-of-origin specific manner are considered to be subject to genomic imprinting, the most well understood form of epigenetic regulation of gene expression in mammals. The observed differences in allele specific gene expression for imprinted genes are not attributable to differences in DNA sequence information, but to specific chemical modifications of DNA and chromatin proteins. Since the discovery of genomic imprinting some three decades ago, over 100 imprinted mammalian genes have been identified and considerable advances have been made in uncovering the molecular mechanisms regulating imprinted gene expression. While most genomic imprinting studies have focused on mouse models and human biomedical disorders, recent work has highlighted the contributions of imprinted genes to complex trait variation in domestic livestock species. Consequently, greater understanding of genomic imprinting and its effect on agriculturally important traits is predicted to have major implications for the future of animal breeding and husbandry. In this review, we discuss genomic imprinting in mammals with particular emphasis on domestic livestock species and consider how this information can be used in animal breeding research and genetic improvement programs.

Ovariectomy in young prepubertal dairy heifers causes complete suppression of mammary progesterone receptors

Mammary growth and development depends on ovarian steroids and particularly interaction of estrogen and progesterone with their intracellular receptors. The objectives of this study were to determine the effect of ovariectomy on the expression of protein and messenger RNA for estrogen receptor-alpha (ESR1) and progesterone receptor (PGR) and their relation to mammary ductal development and cell proliferation. Prepubertal Holstein heifers 2, 3, or 4 mo of age were randomly assigned to one of 2 treatments, ovariectomized (OVX; n = 8) or sham operated (INT; n = 12). Mammary parenchymal (PAR) tissue samples were harvested 30 d after surgery. Localization and quantitation of ESR1 and PGR in PAR were determined by immunohistochemistry and quantitative multispectral imaging. Relative messenger RNA expression of ESR1 and PGR in PAR was measured by quantitative real time polymerase chain reaction. We observed the complete absence of PGR-positive epithelial cell nuclei and reduced PGR transcript abundance in mammary parenchyma of OVX heifers. The percent of epithelial cells expressing ESR1 did not differ by treatment but was decreased with age. However, average intensity of ESR1 expression per cell was reduced in OVX heifers. The abundance of Ki67 labeled epithelial cells and stromal cells was reduced after ovariectomy. These data suggest that reduced mammary development after ovariectomy may be mediated by loss of PGR expression and reduced ESR1 expression in positive cells. A presumptive relationship with ovarian-derived circulating estradiol remains unresolved, but data suggest other ovarian-derived agents may play a role. Use of specific antagonists to manipulate expression or action of PGR and ESR1 receptors should provide direct evidence for roles of these receptors in prepubertal bovine mammary development.

The association between polymorphism of the GH1 gene and changes in protein structure and carcass traits in Mehraban sheep (Ovis aries)

The present study indicates an association between carcass traits and genetic polymorphism and changes in the protein structure of the growth hormone 1 (GH1) gene in Mehraban sheep. Polymorphism of the GH1 gene was detected by polymerase chain reaction–single strand conformation polymorphism (PCR–SSCP) and DNA sequencing methods in 463 individuals. Two different structures in the GH1 protein and six single nucleotide polymorphisms were identified. The association of these SSCP patterns and protein structures with carcass traits was analysed. The SSCP patterns were shown to be associated with carcass traits. Individuals with AB SSCP pattern and Type B protein structure had significantly higher fat-tail weight and volume (P < 0.05) than did those individuals with CC SSCP pattern and Type A protein structure. Moreover, CC SSCP pattern and Type A protein structure contributed to low concentration of blood triglycerides (P = 0.004). The results confirmed the importance of GH1 as a candidate gene for marker-assisted selection for carcass-trait variations in sheep.

Unmasking Upstream Gene Expression Regulators with miRNA-corrected mRNA Data

Expressed micro-RNA (miRNA) affects messenger RNA (mRNA) abundance, hindering the accuracy of upstream regulator analysis. Our objective was to provide an algorithm to correct such bias. Large mRNA and miRNA analyses were performed on RNA extracted from bovine liver and mammary tissue. Using four levels of target scores from TargetScan (all miRNA:mRNA target gene pairs or only the top 25%, 50%, or 75%). Using four levels of target scores from TargetScan (all miRNA:mRNA target gene pairs or only the top 25%, 50%, or 75%) and four levels of the magnitude of miRNA effect (ME) on mRNA expression (30%, 50%, 75%, and 83% mRNA reduction), we generated 17 different datasets (including the original dataset). For each dataset, we performed upstream regulator analysis using two bioinformatics tools. We detected an increased effect on the upstream regulator analysis with larger miRNA:mRNA pair bins and higher ME. The miRNA correction allowed identification of several upstream regulators not present in the analysis of the original dataset. Thus, the proposed algorithm improved the prediction of upstream regulators.

Establishment of mammary gland model in vitro: culture and evaluation of a yak mammary epithelial cell line

This study aimed to establish yak mammary epithelial cells (YMECs) for an in vitro model of yak mammary gland biology. The primary culture of YMECs was obtained from mammary gland tissues of lactating yak and then characterized using immunocytochemistry, RT-PCR, and western blot analysis. Whether foreign genes could be transfected into the YMECs were examined by transfecting the EGFP gene into the cells. Finally, the effect of Staphylococcus aureus infection on YMECs was determined. The established YMECs retained the mammary epithelial cell characteristics. A spontaneously immortalized yak mammary epithelial cell line was established and could be continuously subcultured for more than 60 passages without senescence. The EGFP gene was successfully transferred into the YMECs, and the transfected cells could be maintained for a long duration in the culture by continuous subculturing. The cells expressed more antimicrobial peptides upon S.aureus invasion. Therefore, the established cell line could be considered a model system to understand yak mammary gland biology.

Pharmacological overview of galactogogues

Galactogogues are substances used to induce, maintain, and increase milk production, both in human clinical conditions (like noninfectious agalactias and hypogalactias) and in massification of production in the animal dairy industry. This paper aims to report the state of the art on the possible mechanisms of action, effectiveness, and side effects of galactogogues, including potential uses in veterinary and human medicine. The knowledge gaps in veterinary clinical practice use of galactogogues, especially in the standardization of the lactogenic dose in some pure drugs and herbal preparations, are reviewed.

Imprinted loci in domestic livestock species as epigenomic targets for artificial selection of complex traits

The phenomenon of genomic imprinting, whereby a subset of mammalian genes display parent-of-origin-specific monoallelic expression, is one of the most active areas of epigenetics research. Over the past two decades, more than 100 imprinted mammalian genes have been identified, while considerable advances have been made in elucidating the molecular mechanisms governing imprinting. These studies have helped to unravel the epigenome--a separate layer of regulatory information contained in eukaryotic chromosomes that influences gene expression and phenotypes without involving changes to the underlying DNA sequence. Although most studies of genomic imprinting in mammals have focussed on mouse models or human biomedical disorders, there is burgeoning interest in the phenotypic effects of imprinted genes in domestic livestock species. In particular, research has focused on imprinted genes influencing foetal growth and development, which are associated with economically important production traits in cattle, sheep and pigs. These findings, when coupled with the data emerging from the various different livestock genome projects, have major implications for the future of animal breeding, health and management. Here, we review current scientific knowledge regarding genomic imprinting in livestock species and evaluate how this information can be used in modern livestock improvement programmes.

Short communication: Expression of T-box 2 and 3 in the bovine mammary gland

To increase our understanding of the mechanisms by which growth hormone (GH) and insulin-like growth factor (IGF)-I influence bovine mammary gland development, the potential roles of T-box2 (TBX2) and T-box3 (TBX3) were investigated. Although no information regarding expression of either transcription factor in the bovine mammary gland exists, it is known that TBX3 and its closely related family member, TBX2, are required for mammary gland development in humans and mice. Additionally, TBX3 mutations in humans and mice lead to ulnar mammary syndrome. Evidence is present in bone that TBX3 is required for proliferation and its expression is regulated by GH, an important regulator of mammary gland development and milk production. We hypothesized that TBX2 and TBX3 are expressed in the bovine mammary gland and that GH, IGF-I, or both increase TBX2 and TBX3 expression in bovine mammary epithelial cells (MEC). Bovine mammary gland tissue, MAC-T cells, primary MEC, and fibroblasts were obtained and TBX2 and TBX3 expression was determined by real-time reverse transcription PCR. In addition, TBX2 and TBX3 expression was examined in cells treated with 100 or 500 ng/mL of GH or 100 or 200 ng/mL of IGF-I for 24 or 48 h. Both TBX2 and TBX3 were expressed in bovine mammary tissue. Surprisingly, expression of TBX2 was only detected in mammary fibroblast cells, whereas TBX3 was expressed in all 3 cell types. Growth hormone did not alter TBX3 expression in MAC-T cells or MEC. However, IGF-I increased TBX3 expression in MAC-T, but not in primary MEC. We did not observe a change in TBX2 or TBX3 expression in fibroblasts treated with GH and IGF. Therefore, we concluded that (1) TBX2 and TBX3 are expressed in bovine mammary gland, (2) their expression is cell-type specific, and (3) IGF-I stimulates TBX3 expression in MAC-T cells.

The role of tight junctions in mammary gland function

Tight junctions (TJ) are cellular structures that facilitate cell-cell communication and are important in maintaining the three-dimensional structure of epithelia. It is only during the last two decades that the molecular make-up of TJ is becoming unravelled, with two major transmembrane-spanning structural protein families, called occludin and claudins, being the true constituents of the TJ. These TJ proteins are linked via specific scaffolding proteins to the cell's cytoskeleton. In the mammary gland TJ between adjacent secretory epithelial cells are formed during lactogenesis and are instrumental in establishing and maintaining milk synthesis and secretion, whereas TJ integrity is compromised during mammary involution and also as result of mastitis and periods of mammary inflamation (including mastitis). They prevent the paracellular transport of ions and small molecules between the blood and milk compartments. Formation of intact TJ at the start of lactation is important for the establishment of the lactation. Conversely, loss of TJ integrity has been linked to reduced milk secretion and mammary function and increased paracellular transport of blood components into the milk and vice versa. In addition to acting as a paracellular barrier, the TJ is increasingly linked to playing an active role in intracellular signalling. This review focusses on the role of TJ in mammary function of the normal, non-malignant mammary gland, predominantly in ruminants, the major dairy producing species.

Holsteins favor heifers, not bulls: biased milk production programmed during pregnancy as a function of fetal sex

Mammalian females pay high energetic costs for reproduction, the greatest of which is imposed by lactation. The synthesis of milk requires, in part, the mobilization of bodily reserves to nourish developing young. Numerous hypotheses have been advanced to predict how mothers will differentially invest in sons and daughters, however few studies have addressed sex-biased milk synthesis. Here we leverage the dairy cow model to investigate such phenomena. Using 2.39 million lactation records from 1.49 million dairy cows, we demonstrate that the sex of the fetus influences the capacity of the mammary gland to synthesize milk during lactation. Cows favor daughters, producing significantly more milk for daughters than for sons across lactation. Using a sub-sample of this dataset (N = 113,750 subjects) we further demonstrate that the effects of fetal sex interact dynamically across parities, whereby the sex of the fetus being gestated can enhance or diminish the production of milk during an established lactation. Moreover the sex of the fetus gestated on the first parity has persistent consequences for milk synthesis on the subsequent parity. Specifically, gestation of a daughter on the first parity increases milk production by ∼ 445 kg over the first two lactations. Our results identify a dramatic and sustained programming of mammary function by offspring in utero. Nutritional and endocrine conditions in utero are known to have pronounced and long-term effects on progeny, but the ways in which the progeny has sustained physiological effects on the dam have received little attention to date.

Staphylococcus aureus chronic intramammary infection modifies protein expression of transforming growth factor beta (TGF-β) subfamily components during active involution

The objectives of this study were to determine whether Staphylococcus aureus chronic intramammary infection (IMI) influences protein expression of TGF-β subfamily components and collagen I and to examine the histomorphometric changes that occur in mammary stroma and parenchyma during active mammary gland involution. Twenty-one Holstein non-pregnant cows in late lactation either uninfected or with chronic natural S. aureus IMI were included in this study. Cows were slaughtered at 7, 14 and 21d after cessation of milking and samples for immunohistochemical and morphometric analysis were taken. Protein expression of TGF-β1, TGF-β2 and TGF-β3 was significantly higher in chronically infected quarters than in uninfected controls at the three involution stages studied. Immunostaining of TGF-βR1 and TGF-βR3 and collagen I was significantly higher in S. aureus-infected quarters than in uninfected controls at every involution time evaluated. The percentages of tissue area composed of parenchyma and intralobular stroma were significantly higher in S. aureus-infected than in uninfected quarters. Chronic S. aureus mastitis modifies protein expression of the three TGF-β isoforms and type 1 and 3 receptors, which was associated with changes directed to limit the scope of inflammation and injury to the host.

Short-chain fatty acids inhibit growth hormone and prolactin gene transcription via cAMP/PKA/CREB signaling pathway in dairy cow anterior pituitary cells

Short-chain fatty acids (SCFAs) play a key role in altering carbohydrate and lipid metabolism, influence endocrine pancreas activity, and as a precursor of ruminant milk fat. However, the effect and detailed mechanisms by which SCFAs mediate bovine growth hormone (GH) and prolactin (PRL) gene transcription remain unclear. In this study, we detected the effects of SCFAs (acetate, propionate, and butyrate) on the activity of the cAMP/PKA/CREB signaling pathway, GH, PRL, and Pit-1 gene transcription in dairy cow anterior pituitary cells (DCAPCs). The results showed that SCFAs decreased intracellular cAMP levels and a subsequent reduction in PKA activity. Inhibition of PKA activity decreased CREB phosphorylation, thereby inhibiting GH and PRL gene transcription. Furthermore, PTX blocked SCFAs- inhibited cAMP/PKA/CREB signaling pathway. These data showed that the inhibition of GH and PRL gene transcription induced by SCFAs is mediated by Gi activation and that propionate is more potent than acetate and butyrate in inhibiting GH and PRL gene transcription. In conclusion, this study identifies a biochemical mechanism for the regulation of SCFAs on bovine GH and PRL gene transcription in DCAPCs, which may serve as one of the factors that regulate pituitary function in accordance with dietary intake.

Establishment and characterization of dairy cow growth hormone secreting anterior pituitary cell model

A dairy cow anterior pituitary cell (DCAPC) model was established in vitro for the study of growth hormone (GH) synthesis and secretion in the anterior pituitary gland of the dairy cow. Pituitary glands were obtained from Holstein dairy cows' heads cut by electric saw, and the posterior pituitary glands were removed to obtain integrated anterior pituitary glands. Immunohistochemistry assay of GH in the anterior pituitary glands showed that most somatotrophs were located within the lateral wings of the anterior pituitary. Tissues of the lateral wings of the anterior pituitary were dispersed and cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum. The DCAPCs displayed a monolayer, cobblestone, epithelial-like morphology which are the typical characteristics of the anterior pituitary cells. The DCAPCs were subcultured continuously over ten passages. GH immunoreactivity was present in DCAPCs at passage 10. The transcription of the bovine GH mRNA in DCAPCs at passage 10 was decreased to below 50% compared with the lateral wings of the anterior pituitary tissues. Thus, our DCAPCs model is effective for the in vitro examination of GH synthesis and secretion in the dairy cow anterior pituitary gland. The effects of transforming growth factor beta 1 (TGF-β1) and interferon-γ (IFN-γ) on the expression of GH mRNA in DCAPCs at passage 3 were also investigated. There were no obvious changes in transcription of the GH gene after treatment with TGF-β1 for 24 h, while IFN-γ increased transcription of the GH gene in a dose-dependent manner.

Identification of novel SNPs in the Sarda breed goats POU1F1 gene and their association with milk productive performance

The aim of the study was to detect polymorphism in the POU1F1 gene in Sarda breed goat, as well as to establish if SNPs could be associated with milk productive traits. The research was conducted on 129 Sarda breed goats from 4 to 5 years old, multiparous, lactating and in their third to fifth lactation. We report nine exonic and seven non-coding regions SNPs within the Sarda goat POU1F1 gene, namely, Ex 1 61 G>C; Ex 1 108 G>A; Ex 3 C>T; Ex 3 92 C>T; Ex 4 110 A>G; Ex 5 34 G>A resulting in Arg213Lys change; IVS4 641 G>A, IVS4 643 A>C, IVS4 659 G>A, IVS4 677 A>C, IVS4 G699Del, IVS4 709 C>G, Ex 6 17 G>A resulting in Arg228Ser change, Ex 6 58 G>T, Ex 6 172 T>C, 3'UTR 110 T>C. A statistically significant association was found between genotype TT, in position 17 of the exon 6 (3.1 % of frequency), and increased milk yield (P < 0.01) while genotype GT (25.6 % of frequency) was associated with a higher fat content. Genotype TT in position 58 of the exon 6 (3.9 % of frequency) was found to be associated with a higher fat (P < 0.01) and protein content (P < 0.05). Twenty-eight haplotypes were detected, but no significant association between the haplotypes and the milk production traits have been found. Our data, as well as providing new SNPs extending the POU1F1 gene characterization, evidence a relationship between polymorphism and milk production traits in Sarda goat breed.

MiR-15a decreases bovine mammary epithelial cell viability and lactation and regulates growth hormone receptor expression

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate the expression of target genes at the post-transcriptional level by transcript degradation or translational inhibition. The role of bta-miR-15a in bovine mammary gland hasn’t been reported. Using miRNAs prediction software, GHR gene was predicted to be a potential target of bta-miR-15a. In this study, bovine mammary epithelial cell line was used as an in vitro cell model to address the function of bta-miR-15a on bovine mammary epithelial cells. The expression changes of bta-miR-15a and Ghr after bta-miR-15a transfection were detected by qRT-PCR; the expression of GHR protein and casein was detected by western blotting. To determine whether bta-miR-15a can affect cell viability, cells were examined using an electronic Coulter counter (CASY-TT). In conclusion, bta-miR-15a inhibited the expression of casein of bovine mammary epithelial cells, and cell number and viability were reduced by bta-miR-15a expression. Bta-miR-15a inhibited the viability of mammary epithelial cells as well as the expression of GHR mRNA and protein level, therefore suggesting that bta-miR-15a may play an important role in mammary gland physiology.

Genetic markers of body composition and carcass quality in grazing Brangus steers

The somatotropic axis is a major regulatory pathway of energy metabolism during postnatal growth in mammals. Genes involved in this pathway influence many economically important traits. The association of selected SNPs in these genes with carcass traits was examined in grazing Brangus steers. These traits included final live weight, ultrasound backfat thickness (UBFT), rib-eye area, kidney fat weight, hot carcass weight, and intramuscular fat percentage (%IMF). Genomic DNA (N = 246) was genotyped for a panel of 15 tag SNPs located in the growth hormone receptor (GHR), insulin-like growth factor I, insulin-like growth factor-binding protein 6, pro-melanin-concentrating hormone, suppressor of cytokine signaling 2, and signal transducer and activator of transcription 6 (STAT6) genes. Allelic and haplotype frequencies were compared with those of a sample of European breeds (N = 177 steers). Two tag SNPs in the GHR affected %IMF; one of them (ss86273136) was also strongly associated with UBFT (P < 0.003). The frequency of the most favorable GHR haplotype for %IMF was lower in Brangus steers. Moreover, the haplotype carrying two unfavorable alleles was present at a frequency of 31% in this group. Four tag SNPs on STAT6 had a significant effect on UBFT. One of these, SNP ss115492467, was also associated with %IMF. The STAT6 haplotype, including all the alleles favoring UBFT, was the most abundant variant (34%) in the European cattle, while it had a frequency of 14% in the Brangus steers. The four less favorable variants (absent in the European cattle) were found at a frequency of 38% in the Brangus steers. These results support the association of GHR and STAT6 SNP with carcass traits in composite breeds, such as Brangus, under grazing conditions.

Mastitis and its impact on structure and function in the ruminant mammary gland

It is a given in biology that structure and function go hand-in-hand. At the level of the mammary alveoli, copious milk production depends on the proliferation of mammary epithelial cells and the biochemical and structural differentiation of these cells after parturition. For example, data from quantitative structural studies demonstrate that differences in milk production between beef and dairy cows correspond with a relative failure of alveolar cell differentiation in cattle not specifically selected for milk yield. It is likely, but not proven, that production differences within or between dairy breeds are also determined by differences in the capacity of alveolar cells to differentiate or to maintain an adequate state of differentiation. These observations strongly support the belief that insults from mastitis that lead to losses in mammary function are directly related to disruption of alveolar cell integrity, sloughing of cells, induced apoptosis, and increased appearance of poorly-differentiated cells. Ironically, reduced milk production in cases of subclinical mastitis, is also associated with increases in milk somatic cell count. Thus the elevated neutrophil migration evoked to fight inflammation can inadvertently rendered alveolar epithelial cells non-secretory. A challenge to future researchers will be to devise mastitis treatments and therapies that prevent and/or repair damage to alveolar structure and maximize subsequent secretory cell differentiation.

Effect of pregnancy on the genetic evaluation of dairy cattle

We investigated the effect of stage of pregnancy on estimates of breeding values for milk yield and milk persistency in Gyr and Holstein dairy cattle in Brazil. Test-day milk yield records were analyzed using random regression models with or without the effect of pregnancy. Models were compared using residual variances, heritabilities, rank correlations of estimated breeding values of bulls and cows, and number of nonpregnant cows in the top 200 for milk yield and milk persistency. The estimates of residual variance and heritabilities obtained with the models with or without the effect of pregnancy were similar for the two breeds. Inclusion of the effect of pregnancy in genetic evaluation models for these populations did not affect the ranking of cows and sires based on their predicted breeding values for 305-day cumulative milk yield. In contrast, when we examined persistency of milk yield, lack of adjustment for the effect of pregnancy overestimated breeding values of nonpregnant cows and cows with a long days open period and underestimated breeding values of cows with a short days open period. We recommend that models include the effect of days of pregnancy for estimation of adjustment factors for the effect of pregnancy in genetic evaluations of Dairy Gyr and Holstein cattle.

Polymorphisms of caprine POU1F1 gene and their association with litter size in Jining Grey goats

Seven pairs of primers were designed to amplify 5' promoter region, six exons and partial introns and to detect the polymorphisms of POU1F1 gene in five goat breeds with different prolificacy. The results showed that six mutations were identified in caprine POU1F1 gene including C256T in exon 3, C53T and T123G in intron 3, and G682T (A228S), T723G and C837T in exon 6. The former four mutations were novel SNPs in goat POU1F1 gene. The 53 and 123 loci were in complete linkage disequilibrium in five caprine breeds. Regarding the 256 locus, the Jining Grey goat does with genotype CT had 0.66 kids more than those with genotype CC (P < 0.05), while does with genotype GT had 0.63 (P < 0.05) kids more than those with genotype GG at the 682 locus. The present study preliminarily showed an association between allele T at the 256 and 682 loci of POU1F1 gene and high litter size in Jining Grey goats. Totally 16 haplotypes and 50 genotypes were identified at the above six loci in POU1F1 gene of five goat breeds. Three common haplotypes (hap2, hap3 and hap4) were identified in five goat breeds joined. Four specific haplotypes (hap7, hap9, hap11 and hap13) were detected in Jining Grey goats. The predominant haplotype was hap1 (35.29% and 48.25%) in both Jining Grey and Guizhou White goats, while hap4 (50%) in Boer goats, and hap2 (42.86% and 38.75%) in both Wendeng Dairy and Liaoning Cashmere goats. The most frequent genotypes at six loci in the above five goat breeds were hap1/hap2 (14.38%) and hap1/hap4 (14.38%), hap1/hap2 (38.60%), hap4/hap4 (40.91%), hap2/hap4 (26.53%), hap2/hap5 (20.00%), respectively. The Jining Grey goat does with nine genotypes analyzed of POU1F1 gene showed no obvious difference in litter size.

Single Nucleotide Polymorphisms in the Insulin-Like Growth Factor 1 (IGF-1) Gene are Associated with Performance in Holstein-Friesian Dairy Cattle

Insulin-like growth factor 1 (IGF-1) has been shown to be associated with fertility, growth, and development in cattle. The aim of this study was to (1) identify novel single nucleotide polymorphisms (SNPs) in the bovine IGF-1 gene and alongside previously identified SNPs (2) determine their association with traits of economic importance in Holstein-Friesian dairy cattle. Nine novel SNPs were identified across a panel of 22 beef and dairy cattle by sequence analysis of the 5′ promoter, intronic, and 3′ regulatory regions, encompassing ~5 kb of IGF-1. Genotyping and associations with daughter performance for milk production, fertility, survival, and measures of body size were undertaken on 848 Holstein-Friesian AI sires. Using multiple regression analysis nominal associations (P < 0.05) were identified between six SNPs (four novel and two previously identified) and milk composition, survival, body condition score, and body size. The C allele of AF017143 a previously published SNP (C-512T) in the promoter region of IGF-1 predicted to introduce binding sites for transcription factors HSF1 and ZNF217 was associated (P < 0.05) with increased cow carcass weight (i.e., an indicator of mature cow size). Novel SNPs were identified in the 3′ region of IGF-1 were associated (P < 0.05) with functional survival and chest width. The remaining four SNPs, all located within introns of IGF-1 were associated (P < 0.05) with milk protein yield, milk fat yield, milk fat concentration, somatic cell score, carcass conformation, and carcass fat. Results of this study further demonstrate the multifaceted influences of IGF-1 on milk production and growth related traits in cattle.