Calcium and vitamin D metabolism during lactation

A review of calcium and phosphorus requirement estimates for gestating and lactating sows

Calcium (Ca) and phosphorus (P) are minerals involved in biological functions and essential structural components of the skeleton. The body tightly regulates Ca and P to maintain homeostasis. Maternal needs for Ca and P increase during gestation and lactation to support conceptus growth and milk synthesis. Litter size and litter average daily gain (ADG) have a large effect on Ca and P requirements for sows because as they increase, the requirements increase due to a greater need from the sow. The objective of this review was to summarize published literature on Ca and P requirements in gestating and lactating sows derived from empirical data and factorial models. A total of nine empirical studies and seven factorial models were reviewed for determining the Ca and P requirements in gestation. For lactation, there were six empirical studies and seven factorial models reviewed. Empirical studies determined requirements based on the observed effect of Ca and P on bone mineralization, sow and litter performance, and milk characteristics. Factorial models generated equations to estimate Ca and P requirements using the main components of maintenance, fetal and placental growth, and maternal retention in gestation. The main components for factorial equations in lactation include maintenance and milk production. In gestation, the standardized total tract digestible phosphorus (STTD P) requirement estimates from empirical studies range from 5.4 to 9.5 g/d with total Ca ranging from 12.9 to 18.6 g/d to maximize bone measurements or performance criteria. According to the factorial models, the requirements increase throughout gestation to meet the needs of the growing fetuses and range from 7.6 to 10.6 g/d and 18.4 to 38.2 g/d of STTD P and total Ca, respectively, on day 114 of gestation for parity 1 sows. During lactation, STTD P requirement estimates from empirical studies ranged from 8.5 to 22.1 g/d and total Ca ranged from 21.2 to 50.4 g/d. For the lactation factorial models, STTD P requirements ranged from 14.2 to 25.1 g/d for STTD P and 28.4 to 55.6 g/d for total Ca for parity 1 sows with a litter size of 15 pigs. The large variation in requirement estimates makes it difficult to define Ca and P requirements; however, a minimum level of 6.0 and 22.1 g/d of STTD P during gestation and lactation, respectively, appears to be adequate to meet basal requirements. The limited data and high variation indicate a need for future research evaluating Ca and P requirements for gestating and lactating sows.

Calcium dynamics and associated temporal patterns of milk constituents in early-lactation multiparous Holsteins

At the onset of lactation, calcium (Ca) homeostasis is challenged. For the transitioning dairy cow, inadequate responses to this challenge may result in subclinical hypocalcemia at some point in the postpartum period. It has been proposed that dynamics of blood Ca and the timing of subclinical hypocalcemia allow cows to be classified into 4 Ca dynamic groups by assessing serum total Ca concentrations (tCa) at 1 and 4 days in milk (DIM). These differing dynamics are associated with different risks of adverse health events and suboptimal production. Our prospective cohort study aimed to characterize the temporal patterns of milk constituents in cows with differing Ca dynamics to investigate the potential of Fourier-transform infrared spectroscopic (FTIR) analysis of milk as a diagnostic tool for identifying cows with unfavorable Ca dynamics. We sampled the blood of 343 multiparous Holsteins on a single dairy in Cayuga County, New York, at 1 and 4 DIM and classified these cows into Ca dynamic groups using threshold concentrations of tCa (1 DIM: tCa <1.98 mmol/L; 4 DIM: tCa <2.22 mmol/L) derived from receiver operating characteristic curve analysis based on epidemiologically relevant health and production outcomes. We also collected proportional milk samples from each of these cows from 3 to 10 DIM for FTIR analysis of milk constituents. Through this analysis we estimated the milk constituent levels of anhydrous lactose (g/100 g of milk and g/milking), true protein (g/100 g of milk and g/milking), fat (g/100 g of milk and g/milking), milk urea nitrogen (mg/100 g of milk), fatty acid (FA) groups including de novo, mixed origin, and preformed FA measured in grams/100 g of milk, by relative percentage, and grams/milking, as well as energy-related metabolites including ketone bodies and milk-predicted blood nonesterified FA. Individual milk constituents were compared among groups at each time point and over the entire sample period using linear regression models. Overall, we found differences among the constituent profiles of Ca dynamic groups at approximately every time point and over the entire sample period. The 2 at-risk groups of cows did not differ from each other at more than one time point for any constituent, however prominent differences existed between the milk of normocalcemic cows and the milk of the other Ca dynamic groups with respect to FA. Over the entire sample period, lactose and protein yield (g/milking) were lower in the milk of at-risk cows than in the milk of the other Ca dynamic groups. In addition, milk yield per milking followed patterns consistent with previous Ca dynamic group research. Though our use of a single farm does limit the general applicability of these findings, our conclusions provide evidence that FTIR may be a useful method for discriminating between cows with different Ca dynamics at time points that may be relevant in the optimization of management or development of clinical intervention strategies.

Relationship between calcium dynamics and inflammatory status in the transition period of dairy cows

Improvements in nutrition, management, and genetics of dairy cows over the last several decades have shifted research focus from clinical diseases to subclinical disorders, to which transition cows are particularly vulnerable. Recent studies on the characterization of subclinical hypocalcemia (SCH) indicate that the combined analysis of the degree, timing of suboptimal blood Ca concentration, and duration are most reflective of the disorder. Therefore, the understanding of blood Ca dynamics in early postpartum cows has emerged as an avenue to investigate the paths leading to a successful metabolic adaptation to lactation or not. The conundrum has been in defining whether SCH is the cause or a reflection of a greater underlying disorder. Immune activation and systemic inflammation have been proposed to be the root cause of SCH. However, there is a paucity of data investigating the mechanisms of how systemic inflammation can lead to reduced blood Ca concentration in dairy cows. The objective of this review is to discuss the links between systemic inflammation and reduced blood Ca concentration, and studies needed to advance knowledge on the interface between systemic inflammation and Ca metabolism for the transition dairy cow.

Mortality and morbidity in ageing men: Biology, Lifestyle and Environment

Males live shorter lives than women in all countries. The universality of shorter male life expectancy is a 21st Century phenomena. It occurs with the decline in infectious diseases and the rise in cardiovascular diseases accounting for mortality. Male/female differences in morbidity are not as succinctly characterized. Men have a higher prevalence of lethal diseases, which is linked to their lower life expectancy. Women have more non-lethal conditions such as depression and arthritis; which may also be linked in part to longer survival. Men have better physical functioning and less disability which is partly explained by gender differences in diseases and also by their greater strength, size, and stamina. Gender differences in risk factors for disease have changed over time with the prevalence and treatment of risk as well as differential behavior by gender. Examination of what are seen as basic molecular and cellular measures related to aging indicates men age faster than women; however, even these basic biological measures result from a combination of biology, behavior, and social factors.

Changes of Plasma Analytes Reflecting Metabolic Adaptation to the Different Stages of the Lactation Cycle in Healthy Multiparous Holstein Dairy Cows Raised in High-Welfare Conditions

Simple Summary

This study investigates the changes occurring in plasma analytes of healthy multiparous Holstein dairy cows during the dry, the postpartum, the early and the late lactation phases. A welfare assessment at the herd level and a retrospective subclinical diseases screening were used as blocking factors for the selection of reference individuals. Thus, this study provides measurements of the physiological variations affecting plasma analytes concentrations during the pivotal stages of the lactation cycle in a healthy, high welfare-raised subset of reference individuals and suggest an explanation for the underlying processes involved. Finally, we propose reference intervals for plasma analytes in the stages investigated.

Abstract

Here, we tested the changes occurring in several plasma analytes during different stages of the lactation cycle of high welfare raised multiparous Holstein cows, and provided reference intervals (RI) for plasma analytes concentrations. Eleven high-welfare farms (HWF) located in Northern Italy were selected and their herds used to recruit 361 clinically healthy cows undergoing the dry (from −30 to −10 days from real calving; DFC), the postpartum (from 3 to 7 DFC), the early lactation (from 28 to 45 DFC) and the late lactation phases (from 160 to 305 DFC). Cows affected by subclinical diseases (SCD) were retrospectively excluded, and a subset of 285 cows was selected. Data of plasma analytes underwent ANOVA testing using physiological phases as predictors. The individual effect of each phase was assessed using a pairwise t-test assuming p ≤ 0.05 as a significance limit. A bootstrap approach was used to define the reference interval (RI) for each blood analyte within physiological phases having a pairwise t-test p ≤ 0.05. The concentration of nonesterified fatty acids, albumin, cholesterol, retinol, paraoxonase and tocopherol changed throughout all the physiological phases, whereas the concentration of K, alkaline phosphatase and thiol groups remained stable. Triglycerides, Zn, and ferric ion reducing antioxidant power in the dry phase and BHB, Ca, myeloperoxidase, haptoglobin, reactive oxygen metabolites and advanced oxidation of protein product in postpartum differed compared with other physiological phases. During the dry phase, Packed cell volume, Cl, and urea concentrations were similar to during the postpartum phase. Similarly, Na, γ-glutamyl transferase and β-carotene concentrations were similar to during the early lactation phase; fructosamine and bilirubin concentrations were similar to during the late lactation phase. During the postpartum phase, fructosamine and P concentrations were similar to during the early lactation phase, and the aspartate transaminase concentration was similar to during the late lactation phase. During the early lactation phase, Mg, creatinine, total protein, globulin and ceruloplasmin concentrations were similar to during the postpartum phase, while the urea concentration was similar to during the late lactation phase. All these plasma analytes differed among the other phases. This study identifies physiological trends affecting plasma analytes concentrations during the different stages of the lactation cycle and provides a guideline for the duration and magnitude of their changes when animals are healthy and raised in optimal welfare conditions.

Biochemical Bone Markers During the Transition Period Are Not Influenced by Parenteral Treatment With a High Dose of Cholecalciferol but Can Predict Milk Fever in Dairy Cows

Despite being studied extensively, there are still many knowledge gaps in milk fever prevention and it is still a prevalent disease. Various interventions have been used in its prevention; however, none has proven to be entirely effective. The study aimed to assess the effectiveness of high dose vitamin D₃ parenteral (intramuscularly) administration and the mechanism of its action by studying blood minerals and biochemical bone markers. Further, we assessed the potential of biochemical bone markers, measured in the close-up dry period, as predictors of clinical milk fever after calving. The study was conducted on 56 high yielding, clinically healthy dairy cows, before their 4th or higher lactation. They were divided into three groups based on season (summer and winter) and administration (vitamin D). The winter group was considered as the control group. Cows (n = 13) were parenterally administered a single dose of 10 million IU of vitamin D₃ (DUPHAFRAL® D3) ranging between 10 and 2 days before calving (median = 3 days). Each cow was blood sampled once during four sampling period ranges: ~1 month before calving, 10 to 2 days before calving, 12–48 h after calving and 10–20 days after calving. The samples were analyzed for blood minerals, bone specific alkaline phosphatase (bALP) and C-terminal telopeptide of type I collagen (CTx), alkaline phosphatase, and estradiol. Values were compared between samplings and groups. A receiver operating characteristic (ROC) analysis and logistic regression were used to assess the diagnostic accuracy of biochemical bone markers in predicting milk fever. In this study high dose vitamin D₃ supplementation did not statistically reduced the incidence of milk fever (milk fever incidences were 15.4, 39.1, and 25% in the vitamin D, winter and summer groups, respectively). A significant effect of vitamin D₃ administration on blood minerals or biochemical bone markers was not found at any sampling. We found that the use of biochemical bone markers in the close-up dry period to predict clinical milk fever was applicable only in the winter (housed) group. The area under the curve (AUC) for bALP was 0.804 and 0.846 for CTx using ROC analysis. The bALP curve had the best ratio at the cut-off point 13.85 U/L with 90% sensitivity and 64.3% specificity. While CTx had the ratio of 90% sensitivity and 78.6% specificity at the cut-off point 0.149 ng/mL. Close-up dry dairy cows with CTx ≥0.121 ng/mL had a 3.8 times higher chance of succumbing to milk fever. We were unable to prove that high dose vitamin D₃ parenteral administration is a viable technique for milk fever prevention. Biochemical bone markers are a promising tool for predicting milk fever; however, further studies are needed to confirm their clinical use.

Analyzing the genomic and transcriptomic architecture of milk traits in Murciano-Granadina goats

Background

In this study, we aimed to investigate the molecular basis of lactation as well as to identify the genetic factors that influence milk yield and composition in goats. To achieve these two goals, we have analyzed how the mRNA profile of the mammary gland changes in seven Murciano-Granadina goats at each of three different time points, i.e. 78 d (T1, early lactation), 216 d (T2, late lactation) and 285 d (T3, dry period) after parturition. Moreover, we have performed a genome-wide association study (GWAS) for seven dairy traits recorded in the 1st lactation of 822 Murciano-Granadina goats.

Results

The expression profiles of the mammary gland in the early (T1) and late (T2) lactation were quite similar (42 differentially expressed genes), while strong transcriptomic differences (more than one thousand differentially expressed genes) were observed between the lactating (T1/T2) and non-lactating (T3) mammary glands. A large number of differentially expressed genes were involved in pathways related with the biosynthesis of amino acids, cholesterol, triglycerides and steroids as well as with glycerophospholipid metabolism, adipocytokine signaling, lipid binding, regulation of ion transmembrane transport, calcium ion binding, metalloendopeptidase activity and complement and coagulation cascades. With regard to the second goal of the study, the performance of the GWAS allowed us to detect 24 quantitative trait loci (QTLs), including three genome-wide significant associations: QTL1 (chromosome 2, 130.72-131.01 Mb) for lactose percentage, QTL6 (chromosome 6, 78.90-93.48 Mb) for protein percentage and QTL17 (chromosome 17, 11.20 Mb) for both protein and dry matter percentages. Interestingly, QTL6 shows positional coincidence with the casein genes, which encode 80% of milk proteins.

Conclusions

The abrogation of lactation involves dramatic changes in the expression of genes participating in a broad array of physiological processes such as protein, lipid and carbohydrate metabolism, calcium homeostasis, cell death and tissue remodeling, as well as immunity. We also conclude that genetic variation at the casein genes has a major impact on the milk protein content of Murciano-Granadina goats.

Effect of calcium intake and the dietary cation-anion difference during early lactation on the bone mobilization dynamics throughout lactation in dairy cows

This study investigated the consequences of a low supply of dietary Ca with or without a low dietary cation-anion difference (DCAD) during early lactation on bone mobilization and reconstitution during lactation and on the dynamics of milk Ca content. Fifteen multiparous Holstein cows were distributed among 3 treatments 5 weeks before their expected calving date. These treatments differed based on the provision of diets through the first 10 weeks of lactation. During this period, the control treatment (NCa) consisted of a diet providing 100% of the Ca requirement, with a DCAD of 200 mEq/kg dry matter (DM). The LCa (low Ca) and LCaLD (low Ca, low DCAD) treatments consisted of diets providing 70% of the Ca requirement, with a DCAD of 200 and 0 mEq/kg DM, respectively. After 10 weeks, all cows received the same total mixed ration, which was formulated to meet 100% of the Ca requirement. LCa and LCaLD tended to decrease the body retention of Ca at 3 weeks of lactation compared with NCa but affected neither the dynamics of the blood biomarkers of bone formation and resorption during lactation nor the body retention of Ca at 17 weeks of lactation. Cows almost entirely compensated for the decrease in Ca supply caused by LCa and LCaLD by increasing their apparent digestive absorption of Ca at 3 weeks of lactation, whereas their apparent digestive absorption was unaffected by the treatments at 17 weeks of lactation. Milk production tended to be lower throughout lactation with LCa and LCaLD compared with NCa, with a mean difference of 2 kg/d. The results of this study also indicated that measuring the dynamics of milk Ca content during lactation cannot be considered effective for indirectly estimating the dynamics of bone mobilization in cows. The results also suggested that limited Ca intake at the beginning of lactation may have deleterious effects on milk production.

Calcitriol increases nitric oxide production and modulates microbicidal capacity against Mycobacterium bovis in bovine macrophages

Bovine tuberculosis, a re-emerging infectious disease caused by Mycobacterium bovis, can be transmitted to humans. Global prevalence of M. bovis in humans is underestimated and represents a serious public health risk in developing countries. In light of this situation, it is important to note that our understanding of the immunopathogenesis of human tuberculosis can be improved by studying this disease in the bovine model. Stimulation of the bovine innate immune system with calcitriol (1,25(OH)2D3) leads to an increase in bactericidal molecules involved in macrophage antimicrobial activity. It is unknown, however, if calcitriol´s effect on bovine macrophages impacts intracellular bacterial replication. With these considerations in mind, this study sought to investigate the specific role of calcitriol in tuberculosis control in bovine macrophages, in the hopes of uncovering information applicable to human tuberculosis. As such, infection with M. bovis was shown to induce expression of CYP27B1 and VDR genes in macrophages. Moreover, addition of 1,25(OH)2D3 to cultures of macrophages previously infected with mycobacteria and/or activated by LPS triggered cellular expression of nitric oxide synthase (NOS2) and increased nitrite concentrations, both indicators of nitric oxide (NO) production. By means of a microbicidal assay, addition of 1,25(OH)2D3 was seen to increase macrophage phagocytosis and to decrease mycobacterial intracellular replication. Thus, taken together, our results show that calcitriol can help stimulate the innate immune system of bovines by increasing phagocytosis and decreasing intracellular replication of microorganisms, such as M. bovis, in macrophages, through the VDR pathway.

Lactational challenges in transition dairy cows

Lactation evolved to be the core functional system of providing maternal care in mammalian species. The mammary gland provides an ideally composed nutrient source for the newborn. In addition, colostrum provides passive immunisation after birth, and each suckling process supports the establishment and maintenance of a close mother–offspring bonding. The importance of lactation for the survival of the offspring is represented by a high metabolic priority of the mammary gland within the organism of the lactating animal. Therefore, animal breeding for high milk production has been quite successful, and modern breeding methods have allowed an enormous increase in the performance within only few generations of cows. Mainly in early lactation, most of the available nutrients are directed to the mammary gland, both those from feed, and those mobilised from body tissue. Therefore, milk production can be maintained at a high level despite a negative energy balance. However, the high metabolic load and mobilisation of body tissue requires adequate endocrine and metabolic regulation, which can be successful or less successful in individual animals, i.e. the dairy cow population consists of both metabolically robust and metabolically vulnerable dairy cows. While robust animals adapt adequately, vulnerable cows show often high plasma concentrations of non-esterified fatty acids and β-hydroxybutyrate, and are prone to various production-related diseases. In pasture- or forage-based feeding systems, an additional challenge is a limited availability of nutrients for milk production. Forage feeding without complementary concentrate leads to enormous metabolic disorders in high-yielding cows, but is tolerated in dairy cows with a moderate genetic-performance level.

Fine mapping of a QTL on bovine chromosome 6 using imputed full sequence data suggests a key role for the group-specific component (GC) gene in clinical mastitis and milk production

BACKGROUND

Clinical mastitis is an inflammation of the mammary gland and causes significant costs to dairy production. It is unfavourably genetically correlated to milk production, and, thus, knowledge of the mechanisms that underlie these traits would be valuable to improve both of them simultaneously through breeding. A quantitative trait locus (QTL) that affects both clinical mastitis and milk production has recently been fine-mapped to around 89 Mb on bovine chromosome 6 (BTA6), but identification of the gene that underlies this QTL was not possible due to the strong linkage disequilibrium between single nucleotide polymorphisms (SNPs) within this region. Our aim was to identify the gene and, if possible, the causal polymorphism(s) responsible for this QTL through association analysis of high-density SNPs and imputed full sequence data in combination with analyses of transcript and protein levels of the identified candidate gene.

RESULTS

Associations between SNPs and the studied traits were strongest for SNPs that were located within and immediately upstream of the group-specific component (GC) gene. This gene encodes the vitamin D-binding protein (DBP) and has multiple roles in immune defense and milk production. A 12-kb duplication that was identified downstream of this gene covered its last exon and segregated with the QTL allele that is associated with increased mastitis susceptibility and milk production. However, analyses of GC mRNA levels on the available samples revealed no differences in expression between animals having or lacking this duplication. Moreover, we detected no differences in the concentrations of DBP and its ligand vitamin D between the animals with different GC genotypes that were available for this study.

CONCLUSIONS

Our results suggest GC as the gene that underlies the QTL for clinical mastitis and milk production. However, since only healthy animals were sampled for transcription and expression analyses, we could not draw any final conclusion on the absence of quantitative differences between animals with different genotypes. Future studies should investigate GC RNA expression and protein levels in cows with different genotypes during an infection.

Conflict or congruence? Maternal and infant-centric factors associated with shorter exclusive breastfeeding durations among the Tsimane

Six months of exclusive breastfeeding (EBF) is considered optimal for infant health, though globally most infants begin complementary feeding (CF) earlier-including among populations that practice prolonged breastfeeding. Two frameworks for understanding patterns of early CF emerge in the literature. In the first, maternal and infant needs trade-off, as "maternal-centric" factors-related to time and energy demands, reproductive investment, cultural influences, and structural barriers- favor supplanting breastfeeding with earlier and increased CF. A second framework considers that "infant-centric" factors-related to infant energetic needs-favor CF before six months to supplement breastfeeding. We apply these two frameworks in examining early CF among the Tsimane-a high-fertility, high-mortality, forager-horticulturalist population residing in the Bolivian Amazon. Data were collected from a mixed-longitudinal sample of 161 Tsimane mother-infant pairs from August 2012-April 2013. Tsimane mothers generally reported introducing CF because of perceived infant needs. However, CF is introduced with continued intensive breastfeeding, and generally coupled with premastication. Risks of earlier CF relative to the minimum hazard (estimated at 5 births) were elevated for lower and higher parity mothers, but were significantly greater only after 9 births. Seventeen percent of mothers reported introducing CF because of low milk supply. Introducing CF because of low milk was most common from 0 to 3 months of age and among higher parity mothers, which may reflect physiological constraints. Maternal reproductive trade-offs and perceived infant needs may help explain the low prevalence of EBF to six months among other populations in which breastfeeding is not structurally or culturally constrained.

Vitamin D, phosphate, and vasculotoxicity

Vascular calcification is a complex process that results in the ectopic deposition of calcium-phosphate hydroxyapatite. Medial and intimal vascular calcification is frequently present in patients with diabetes mellitus and chronic kidney disease (CKD), and markedly increases the morbidity and mortality of these patients. Increased serum levels of calcium and phosphate, along with the use of active vitamin D metabolites, are commonly implicated in the evolvement of vascular wall mineralization in CKD patients. Because CKD patients have lower serum levels of vitamin D, they are routinely prescribed vitamin D supplements that exert a dualistic role that is both healthful and harmful in these patients, perhaps protecting bone health, but at the expense of promoting vascular pathology. This review briefly explains how reducing the phosphate burden in CKD patients could minimize vitamin-D-associated vascular wall calcification.

Daughter dearest: Sex-biased calcium in mother's milk among rhesus macaques

Mother's milk provides building blocks necessary for infant development and growth postnatally. Minerals in milk are particularly important for infant skeletal development and may reflect maternal characteristics that are associated with the capacity to synthesize milk and sex-specific developmental priorities of the infant. Using a large sample of mother-infant dyads assigned to the outdoor breeding colony at the California National Primate Research Center (N=104), we investigated the relationship of milk calcium (Ca) and phosphorus (P) concentrations and the ratio of Ca/P to maternal and infant characteristics and to other milk variables. Ca and P are largely associated with casein micelles, and as expected, both Ca and P were positively correlated with protein concentrations in milk. Neither Ca nor P concentrations were associated with maternal parity. Mothers rearing daughters tended to produce higher mean Ca concentration in milk, and consequently a higher Ca/P ratio, than did mothers rearing sons, even though protein concentration was not elevated. These results suggest that the Ca/P ratio in rhesus milk may have been under separate selective pressure from protein content to facilitate the accelerated rate of skeletal calcification that has been observed in female Macaca mulatta infants.

Vitamin D signaling in the bovine immune system: a model for understanding human vitamin D requirements

The endocrine physiology of vitamin D in cattle has been rigorously investigated and has yielded information on vitamin D requirements, endocrine function in health and disease, general metabolism, and maintenance of calcium homeostasis in cattle. These results are relevant to human vitamin D endocrinology. The current debate regarding vitamin D requirements is centered on the requirements for proper intracrine and paracrine vitamin D signaling. Studies in adult and young cattle can provide valuable insight for understanding vitamin D requirements as they relate to innate and adaptive immune responses during infectious disease. In cattle, toll-like receptor recognition activates intracrine and paracrine vitamin D signaling mechanism in the immune system that regulates innate and adaptive immune responses in the presence of adequate 25-hydroxyvitamin D. Furthermore, experiments with mastitis in dairy cattle have provided in vivo evidence for the intracrine vitamin D signaling mechanism in macrophages as well as vitamin D mediated suppression of infection. Epidemiological evidence indicates that circulating concentrations above 32 ng/mL of 25-hydroxyvitamin D are necessary for optimal vitamin D signaling in the immune system, but experimental evidence is lacking for that value. Experiments in cattle can provide that evidence as circulating 25-hydroxyvitamin D concentrations can be experimentally manipulated within ranges that are normal for humans and cattle. Additionally, young and adult cattle can be experimentally infected with bacteria and viruses associated with significant diseases in both cattle and humans. Utilizing the bovine model to further delineate the immunomodulatory role of vitamin D will provide potentially valuable insights into the vitamin D requirements of both humans and cattle, especially as they relate to immune response capacity and infectious disease resistance.

Vitamin D and aging: old concepts and new insights

Aging is a complex biological process driven by a selective class of molecules and pathways that affect overall deterioration of physiological functions to increase the risk of age-related diseases. A role of vitamin D in mammalian aging is well documented. Since vitamin D has an essential role in bone formation and mineralization, its deficiency results in impaired bone mineralization, such as rickets in children, osteomalacia in adults and osteoporosis in the aged population. Vitamin D replacement therapy therefore is one of the most commonly prescribed treatments for the elderly. Recent studies using genetically altered mouse models, such as in Fgf-23(-/-) and klotho mutant mice, that exhibit altered mineral ion metabolism due to high vitamin D activities showed features of premature aging that include atherosclerosis, emphysema, osteopenia/osteoporosis, hypogonadism, soft tissue calcifications and generalized atrophy of organs; the pathologic effects of vitamin D in these mouse models are obvious, as diminution or genetic ablation of the vitamin D pathway ameliorated most of the above-mentioned phenotypes, by reversing mineral ion metabolism, and the resultant effect being prolonged survival of the mutant mice. These in vivo mouse studies, although subject to further molecular characterization, add new insights into the role of vitamin D in aging.

The effect of high-dose vitamin D supplementation on serum vitamin D levels and milk calcium concentration in lactating women and their infants

OBJECTIVE

Improve vitamin D status in lactating women and their recipient infants, and measure breast milk calcium concentration [Ca] as a function of vitamin D regimen.

DESIGN/METHODS

Fully breastfeeding mothers were randomized at 1 month postpartum to 2000 (n = 12) or 4000 (n = 13) IU/day vitamin D for 3 months to achieve optimal vitamin D status [serum 25(OH)D > or =32 ng/mL (80 nmol/L)]. Breast milk [Ca], maternal and infant serum 25(OH)D and serum Ca, and maternal urinary Ca/Cr ratio were measured monthly.

RESULTS

Mothers were similar between groups for age, race, gestation, and birth weight. 25(OH)D increased from 1 to 4 months in both groups (mean +/- SD): +11.5 +/- 2.3 ng/mL for group 2000 (p = 0.002) and +14.4 +/- 3.0 ng/mL for group 4000 (p = 0.0008). The 4000 IU/day regimen was more effective in raising both maternal and infant serum levels and breast milk antirachitic activity than the 2000 IU/day regimen. Breast milk [Ca] fell with continued lactation through 4 months in the 2000 and 4000 IU groups. Decline in breast milk [Ca] was not associated with vitamin D dose (p = 0.73) or maternal 25(OH)D (p = 0.94). No mother or infant experienced vitamin D-related adverse events, and all laboratory parameters remained in the normal range.

CONCLUSION

High-dose vitamin D was effective in increasing 25(OH)D levels in fully breastfeeding mothers to optimal levels without evidence of toxicity. Breast milk [Ca] and its decline in both groups during 1 to 4 months were independent of maternal vitamin D status and regimen. Both the mother and her infant attained improved vitamin D status and maintained normal [Ca].

Calcium transport and signaling in the mammary gland: targets for breast cancer

The mammary gland is subjected to extensive calcium loads during lactation to support the requirements of milk calcium enrichment. Despite the indispensable nature of calcium homeostasis and signaling in regulating numerous biological functions, the mechanisms by which systemic calcium is transported into milk by the mammary gland are far from completely understood. Furthermore, the implications of calcium signaling in terms of regulating proliferation, differentiation and apoptosis in the breast are currently uncertain. Deregulation of calcium homeostasis and signaling is associated with mammary gland pathophysiology and as such, calcium transporters, channels and binding proteins represent potential drug targets for the treatment of breast cancer.

Plasma membrane calcium-ATPase 2 and 4 in human breast cancer cell lines

There is evidence to suggest that plasma membrane Ca2+-ATPase (PMCA) isoforms are important mediators of mammary gland physiology. PMCA2 in particular is upregulated extensively during lactation. Expression of other isoforms such as PMCA4 may influence mammary gland epithelial cell proliferation and aberrant regulation of PMCA isoform expression may lead or contribute to mammary gland pathophysiology in the form of breast cancers. To explore whether PMCA2 and PMCA4 expression may be deregulated in breast cancer, we compared mRNA expression of these PMCA isoforms in tumorigenic and non-tumorigenic human breast epithelial cell lines using real time RT-PCR. PMCA2 mRNA has a higher level of expression in some breast cancer cell lines and is overexpressed more than 100-fold in ZR-75-1 cells, compared to non-tumorigenic 184B5 cells. Although differences in PMCA4 mRNA levels were observed between breast cell lines, they were not of the magnitude observed for PMCA2. We conclude that PMCA2 mRNA can be highly overexpressed in some breast cancer cells. The significance of PMCA2 overexpression on tumorigenicity and its possible correlation with other properties such as invasiveness requires further study.

Null Mutation in the Gene Encoding Plasma Membrane Ca2+-ATPase Isoform 2 Impairs Calcium Transport into Milk

The means by which calcium is transported into the milk produced by mammary glands is a poorly understood process. One hypothesis is that it occurs during exocytosis of secretory products via the Golgi pathway, consistent with the observation that the SPCA1 Ca2+-ATPase, which is expressed in the Golgi, is induced in lactating mammary tissue. However, massive up-regulation of the PMCA2bw plasma membrane Ca2+-ATPase also occurs during lactation and is more strongly correlated with increases in milk calcium, suggesting that calcium may be secreted directly via this pump. To examine the physiological role of PMCA2bw in lactation we compared lactating PMCA2-null mice to heterozygous and wild-type mice. Relative expression levels of individual milk proteins were unaffected by genotype. However, milk from PMCA2-null mice had 60% less calcium than milk from heterozygous and wild-type mice, the total milk protein concentration was lower, and an indirect measure of milk production (litter weights) suggested that the PMCA2-null mice produce significantly less milk. In contrast, lactose was higher in milk from PMCA2-null mice during early lactation, but by day 12 of lactation there were no differences in milk lactose between the three genotypes. These data demonstrate that the activity of PMCA2bw is required for secretion of much of the calcium in milk. This major secretory function represents a novel biological role for the plasma membrane Ca2+-ATPases, which are generally regarded as premier regulators of intracellular Ca2+.

The calcium-sensing receptor regulates mammary gland parathyroid hormone-related protein production and calcium transport

The transfer of calcium from mother to milk during lactation is poorly understood. In this report, we demonstrate that parathyroid hormone-related protein (PTHrP) production and calcium transport in mammary epithelial cells are regulated by extracellular calcium acting through the calcium-sensing receptor (CaR). The CaR becomes expressed on mammary epithelial cells at the transition from pregnancy to lactation. Increasing concentrations of calcium, neomycin, and a calcimimetic compound suppress PTHrP secretion by mammary epithelial cells in vitro, whereas in vivo, systemic hypocalcemia increases PTHrP production, an effect that can be prevented by treatment with a calcimimetic. Hypocalcemia also reduces overall milk production and calcium content, while increasing milk osmolality and protein concentrations. The changes in milk calcium content, milk osmolality, and milk protein concentration were mitigated by calcimimetic infusions. Finally, in a three-dimensional culture system that recapitulates the lactating alveolus, activation of the basolateral CaR increases transcellular calcium transport independent of its effect on PTHrP. We conclude that the lactating mammary gland can sense calcium and adjusts its secretion of calcium, PTHrP, and perhaps water in response to changes in extracellular calcium concentration. We believe this defines a homeostatic system that helps to match milk production to the availability of calcium.

Low estrogen and high parathyroid hormone-related peptide levels contribute to accelerated bone resorption and bone loss in lactating mice

Providing enough calcium for milk production stresses calcium homeostasis in lactating mammals. A universal response to these demands for calcium appears to be the mobilization of maternal skeletal reserves, and bone loss during lactation has been well documented. However, the regulation of calcium and skeletal metabolism during lactation remains enigmatic. Our study was designed to examine mineral and bone metabolism in lactating mice. We found that mice lose bone rapidly at all sites during lactation. Bone mineral density as determined by dual-energy x-ray absorptiometry was 20 to 30% lower at the spine, femur, and total body in lactating compared with either age-matched virgin or pregnant mice. The decrease in bone mineral density was accompanied by dramatic reductions in bone volume and changes in trabecular architecture. Bone loss was also accompanied by increases in bone turnover as determined by biochemical markers and histomorphometry. PTHrP levels were elevated during lactation and correlated positively with markers of bone resorption and negatively with bone mass at all sites. Estrogen levels were low during lactation and correlated negatively with bone resorption markers. Finally, estrogen and pamidronate treatment lowered rates of bone resorption to baseline virgin levels and mitigated, but did not prevent, bone loss. These data suggest that the combination of estrogen deficiency and elevations in circulating PTHrP during lactation act to stimulate bone resorption and promote bone loss.

The evolutionary origins of maternal calcium and bone metabolism during lactation

Calcium is required for skeletal growth in all vertebrate offspring. In eutherian mammals, calcium is provided by the mother via the placenta during fetal growth and via milk until weaning. Transferring calcium to offspring during pregnancy and lactation significantly stresses maternal calcium homeostasis. During human pregnancy, the extra calcium requirements are met primarily by an increase in absorption of calcium from the diet and by a modest increase in rates of bone resorption. In nursing mothers, the calcium required for milk production is generated by a dramatic increase in rates of bone resorption and a decrease in the rate of renal calcium excretion. To consider the evolution of these maternal adaptations in bone and calcium metabolism, comparisons are made across different species of mammals, and the fundamental problem of maternal transfer of calcium to young is explored in lower vertebrates. These comparisons suggest that maternal adaptations in calcium and bone metabolism during pregnancy and lactation in mammals originate from adaptations in bone and mineral metabolism that supply calcium for egg production in lower vertebrates.

Ca(2+)-ATPase protein expression in mammary tissue

Protein expression of plasma membrane Ca(2+)-ATPases (PMCAs) and the putative Golgi secretory pathway Ca(2+)-ATPase (SPCA) was examined in rat mammary tissue. As lactation started, PMCA protein expression increased dramatically, and this increased expression paralleled milk production. Mammary PMCA was primarily PMCA2b but was approximately 4,000 daltons larger than expected. RT-PCR showed that the primary mammary PMCA2b transcript was alternatively spliced, at splice site A, to include an additional 135 bp, resulting in the insertion of 45 amino acids. This splice form is designated 2bw. PMCA2bw is secreted into milk, associated with the milk fat globule membrane. Therefore, PMCA2bw is located on the apical membrane of the secretory cell. Smaller amounts of PMCA1b and 4b protein were found in mammary tissue. PMCA4b was the major PMCA expressed in developing tissue, and its level declined as lactation started. PMCA1b expression increased moderately during lactation. SPCA protein expression increased 1 wk before parturition and increased further as lactation proceeded. The abundance and cell location of PMCA2b suggest that it is important for macro-Ca(2+) homeostasis in lactating tissue. The pattern of expression and abundance of SPCA suggest that it is a candidate for the Golgi Ca(2+)-ATPase.

1,25-dihydroxyvitamin D3 enhances milk antibody titers to Escherichia coli J5 vaccine

Recent evidence in cattle and mice has suggested that 1,25-dihydroxyvitamin D3 may stimulate T-lymphocyte differentiation pathways responsible for humoral immunity. The use of 1,25-dihydroxyvitamin D3 as an adjuvant for an Escherichia coli J5 vaccine was tested. Ten midlactation cows received J5 vaccine and were revaccinated 6 wk after the first vaccine administration. Five of these cows were given 200 micrograms of 1,25-dihydroxyvitamin D3, in addition to the primary vaccination, and they received an additional 200 micrograms of 1,25-dihydroxyvitamin D3 1 wk after the primary vaccination. No 1,25-dihydroxyvitamin D3 was administered with the wk 6 J5 vaccine booster. Milk immunoglobin (Ig)M, IgG, and IgA antibodies to E. coli J5 were significantly increased in cows receiving 1,25-dihydroxyvitamin D3 + E. coli J5 vaccine compared with cows that received only E. coli J5 vaccine. Serum IgG and IgG1 antibodies to E. coli J5 were also significantly enhanced by 1,25-dihydroxyvitamin D3 treatment compared with cows receiving vaccine alone. In contrast, serum IgG2 titers tended to decline in cows receiving 1,25-dihydroxyvitamin D3. Taken together, these data suggest that 1,25-dihydroxyvitamin D3 has potential usefulness in boosting humoral responses to vaccines such as J5 and may further enhance the protective qualities of vaccines.

Ca2+-ATPases and their expression in the mammary gland of pregnant and lactating rats

The transcellular Ca2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca2+ concentrations critical to cell function. Ca2+-ATPases play a critical role in the maintenance of this cellular Ca2+ homeostasis. Using RT-PCR and sequencing, we identified six Ca2+ pumps in lactating mammary tissue. Three plasma membrane Ca2+-ATPases (PMCAs) were found (PMCA1b, PMCA2b, and PMCA4b). Two sarco (endo)plasmic reticulum Ca2+-ATPases (SERCAs) were identified (SERCA2 and SERCA3), and the rat homologue to the yeast Golgi Ca2+-ATPase RS-10 was also found. The pattern of mRNA expression of each of these pumps was examined in rat mammary tissue from the 7th day of pregnancy to the 21st day of lactation. Northern blots revealed increased mRNA expression for all Ca2+ pumps by the 14th day of lactation, and transcripts continued to increase through the 18th day of lactation. PMCA1b, PMCA4b, SERCA2, and SERCA3 showed the lowest levels of expression. RS-10 transcripts were more abundant than SERCA2, SERCA3, PMCA1b, and PMCA4b. RS-10 was the only pump to increase in expression before parturition. PMCA2b was the most abundant transcript found in lactating mammary tissue. At peak lactation, expression of PMCA2b approached that of actin. The high expression, high affinity for Ca2+, and high activity at low calmodulin concentrations exhibited by PMCA2b suggest that it is uniquely suited for maintenance of Ca2+ homeostasis in the lactating mammary gland. The pattern of expression and abundance of RS-10 suggest that it is a candidate for the Golgi Ca2+-ATPase shown to be important in maintaining the Golgi Ca2+ concentration required for casein synthesis and micelle formation.