Periparturient Mineral Metabolism: Implications to Health and Productivity

Mineral metabolism, in particular Ca, and to a lesser extent phosphorus (P) and magnesium (Mg), is altered with the onset of lactation because of extensive irreversible loss to synthesize colostrum and milk. The transient reduction in the concentration of Ca in blood, particularly when it lasts days, increases the risk of mineral-related disorders such as hypocalcemia and, to a lesser extent, hypophosphatemia. Although the incidence of clinical hypocalcemia can be reduced by prepartum dietary interventions, subclinical hypocalcemia remains prevalent, affecting up to 60% of the dairy cows in the first 3 d postpartum. More importantly, strong associations exist between hypocalcemia and increased susceptibility to other peripartum diseases and impaired reproductive performance. Mechanistic experiments have demonstrated the role of Ca on innate immune response in dairy cows, which presumably predisposes them to other diseases. Hypocalcemia is not related to inadequate Ca intake as prepartum diets marginal to deficient in Ca reduce the risk of the disease. Therefore, the understanding of how Ca homeostasis is regulated, in particular how calciotropic hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D3, affect blood Ca concentrations, gastrointestinal Ca absorption, bone remodeling, and renal excretion of Ca become critical to develop novel strategies to prevent mineral imbalances either by nutritional or pharmacological interventions. A common method to reduce the risk of hypocalcemia is the manipulation of the prepartum dietary cation-anion difference. Feeding acidogenic diets not only improves Ca homeostasis and reduces hypocalcemia, but also reduces the risk of uterine diseases and improves productive performance. Feeding diets that induce a negative Ca balance in the last weeks of gestation also reduce the risk of clinical hypocalcemia, and recent work shows that the incorporation of mineral sequestering agents, presumably by reducing the absorption of P and Ca prepartum, increases blood Ca at calving, although benefits to production and health remain to be shown. Alternative strategies to minimize subclinical hypocalcemia with the use of vitamin D metabolites either fed prepartum or as a pharmacological agent administered immediately after calving have shown promising results in reducing hypocalcemia and altering immune cell function, which might prove efficacious to prevent diseases in early lactation. This review summarizes the current understanding of Ca homeostasis around parturition, the limited knowledge of the exact mechanisms for gastrointestinal Ca absorption in bovine, the implications of hypocalcemia on the health of dairy cows, and discusses the methods to minimize the risk of hypocalcemia and their impacts on productive performance and health in dairy cows.

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.

Genetic Link Determining the Maternal-Fetal Circulation of Vitamin D

Vitamin D is an essential micronutrient whose demand is heightened during pregnancy to support the growth of the fetus. Furthermore, the fetus does not produce vitamin D and hence relies exclusively on the supply of maternal vitamin D through the placenta. Vitamin D inadequacy is linked with pregnancy complications and adverse infant outcomes. Hence, early predictive markers of vitamin D inadequacy such as genetic vulnerability are important to both mother and offspring. In this multi-ethnic Asian birth cohort study, we report the first genome-wide association analysis (GWAS) of maternal and fetal vitamin D in circulation. For this, 25-hydroxyvitamin D (25OHD) was measured in the antenatal blood of mothers during mid gestation (n=942), and the cord blood of their offspring at birth (n=812). Around ~7 million single nucleotide polymorphisms (SNPs) were regressed against 25OHD concentrations to identify genetic risk variants. About 41% of mothers had inadequate 25OHD (≤75nmol/L) during pregnancy. Antenatal 25OHD was associated with ethnicity [Malay (Β=−22.32nmol/L, p=2.3×10⁻²⁶); Indian (Β=−21.85, p=3.1×10⁻²¹); reference Chinese], age (Β=0.47/year, p=0.0058), and supplement intake (Β=16.47, p=2.4×10⁻¹³). Cord blood 25OHD highly correlated with antenatal vitamin D (r=0.75) and was associated with ethnicity [Malay (Β=−4.44, p=2.2×10⁻⁷); Indian (Β=−1.99, p=0.038); reference Chinese]. GWAS analysis identified rs4588, a missense variant in the group-specific component (GC) gene encoding vitamin D binding protein (VDBP), and its defining haplotype, as a risk factor for low antenatal (Β=−8.56/T-allele, p=1.0×10⁻⁹) and cord blood vitamin D (Β=−3.22/T-allele, p=1.0×10⁻⁸) in all three ethnicities. We also discovered a novel association in a SNP downstream of CYP2J2 (rs10789082), a gene involved in 25-hydroxylation of vitamin D, with vitamin D in pregnant women (Β=−7.68/G-allele, p=1.5×10⁻⁸), but not their offspring. As the prevention and early detection of suboptimal vitamin D levels are of profound importance to both mother and offspring’s health, the genetic risk variants identified in this study allow risk assessment and precision in early intervention of vitamin D deficiency.

Invited review: Cytochrome P450 enzyme involvement in health and inflammatory-based diseases of dairy cattle

Dairy cattle are at the greatest risk of developing diseases around the time of calving because of compromised immune responses and the occurrence of oxidative stress. Both the development of compromised immunity and oxidative stress are influenced directly or indirectly by the metabolism of polyunsaturated fatty acids (PUFA) and fat-soluble vitamins. The cytochrome P450 (CYP450) family of enzymes is central to the metabolism of both classes of these compounds, but to date, the importance of CYP450 in the health of dairy cattle is underappreciated. As certain CYP450 isoforms metabolize both PUFA and fat-soluble vitamins, potential interactions may occur between PUFA and fat-soluble vitamins that are largely unexplored. For example, one CYP450 that generates anti-inflammatory oxylipids from arachidonic acid additionally contributes to the activation of vitamin D. Other potential substrate interactions between PUFA and vitamins A and E may exist as well. The intersection of PUFA and fat-soluble vitamin metabolism by CYP450 suggest that this enzyme system could provide an understanding of how immune function and oxidant status interconnect, resulting in increased postpartum disease occurrence. This review will detail the known contributions of bovine CYP450 to the regulation of oxylipids with a focus on enzymes that may also be involved in the metabolism of fat-soluble vitamins A, D, and E that contribute to antioxidant defenses. Although the activity of specific CYP450 is generally conserved among mammals, important differences exist in cattle, such as the isoforms primarily responsible for activation of vitamin D that makes their specific study in cattle of great importance. Additionally, a CYP450-driven inflammatory positive feedback loop is proposed, which may contribute to the dysfunctional inflammatory responses commonly found during the transition period. Establishing the individual enzyme isoform contributions to oxylipid biosynthesis and the regulation of vitamins A, D, and E may reveal how the CYP450 family of enzymes can affect inflammatory responses during times of increased susceptibility to disease. Determining the potential effect of each CYP450 on disease susceptibility or pathogenesis may allow for the targeted manipulation of the CYP450 pathways to influence specific immune responses and antioxidant defenses during times of increased risk for health disorders.

Serum vitamin D concentrations at dry-off and close-up predict increased postpartum urine ketone concentrations in dairy cattle

Vitamin D is commonly supplemented to dairy cows as vitamin D₃ to support calcium homeostasis and in times of low sunlight exposure. Vitamin D has beneficial immunomodulatory and anti-inflammatory properties. Serum 25-hydroxyvitamin D [25(OH)D] concentrations fluctuated during lactation, with the lowest concentrations measured in healthy cows within 7 d of calving. However, it is unknown if serum 25(OH)D concentrations measured during the previous lactation are associated with transition diseases or health risk factors in dairy cattle. We collected serum samples from 279 dairy cattle from 5 commercial dairy herds in Michigan at dry-off, close-up, and 2-10 d in milk (DIM). Vitamin D concentrations were determined by measuring serum 25(OH)D by radioimmunoassay. Total serum calcium was measured by colorimetric methods. Body condition scores (BCS) were assigned at the time of blood collection. Clinical disease incidence was monitored until 30 d postparturition. Separate bivariable logistic regression analyses were used to determine if serum 25(OH)D at dry-off, close-up, and 2-10 DIM was associated with various clinical diseases including mastitis, lameness, and uterine disorders (classified as metritis, retained placenta, or both) and increased urine ketone concentrations at P < 0.05. Among all significant bivariable analyses, multivariable logistic regression analyses were built to adjust for potential confounding variables including parity, BCS, season, and calcium. Receiver operator characteristic (ROC) curve analyses were used to determine optimal concentrations of serum 25(OH)D. We found that higher serum 25(OH)D concentrations at dry-off and close-up predicted increased urine ketone concentrations in early lactation, even after adjustment for confounders. Alternatively, we found that lower serum 25(OH)D at 2-10 DIM was associated with uterine diseases. Optimal concentrations for serum 25(OH)D at dry-off and close-up for lower risk of increased urine ketone concentrations were below 103.4 and 91.1 ng/mL, respectively. The optimal concentration for serum 25(OH)D at 2-10 DIM for uterine diseases was above 71.4 ng/mL. These results indicate that serum 25(OH)D at dry-off and close-up may be a novel predictive biomarker for increased urine ketone concentrations during early lactation. Increased urine ketone concentrations are not necessarily harmful or diagnostic for ketosis but do indicate development of negative energy balance, metabolic stress, and increased risk of early lactation diseases. Predicting that dairy cattle are at increased risk of disease facilitates implementation of intervention strategies that may lower disease incidence. Future studies should confirm these findings and determine the utility of serum 25(OH)D concentrations as a predictive biomarker for clinical and subclinical ketosis.

Widespread basal cytochrome P450 expression in extrahepatic bovine tissues and isolated cells

Periparturient cattle face increased risk of both metabolic and infectious diseases. Factors contributing to this predisposition include oxidized polyunsaturated fatty acids, also known as oxylipids, whose production is altered during the periparturient period and in diseased cattle. Alterations in the production of oxylipids derived from cytochrome P450 (CYP450) enzymes are over-represented during times of increased disease risk and clinical disease, such as mastitis. Many of these same CYP450 enzymes additionally regulate metabolism of fat-soluble vitamins, such as A, D, and E. These vitamins are essential to maintaining immune health, yet circulating concentrations are diminished near calving. Despite this, a relatively small amount of research has focused on the roles of CYP450 enzymes outside of the liver. The aim of this paper is to describe the relative gene expression of 11 CYP450 in bovine tissues and common in vitro bovine cell models. Eight tissue samples were collected from 3 healthy dairy cows after euthanasia. In vitro samples included primary bovine aortic and mammary endothelial cells and immortalized bovine kidney and mammary epithelial cells. Quantitative real-time-PCR was carried out to assess basal transcript expression of CYP450 enzymes. Surprisingly, CYP450 mRNA was widely expressed in all tissue samples, with predominance in the liver. In vitro CYP450 expression was less robust, with several cell types lacking expression of specific CYP450 enzymes altogether. Overall, cell culture models did not reflect expression of tissue CYP450. However, when CYP450 were organized by activity, certain cell types consistently expressed specific functional groups. These data reveal the widespread expression of CYP450 in individual organs of healthy dairy cows. Widespread expression helps to explain previous evidence of significant changes in CYP450-mediated oxylipid production and fat-soluble vitamin metabolism in organ microenvironments during periods of oxidative stress or disease. As such, these data provide a foundation for targeted functional experiments aimed at understanding the activities of specific CYP450 and associated therapeutic potential during times of increased disease risk.

Feeding supplemental 25-hydroxyvitamin D3 increases serum mineral concentrations and alters mammary immunity of lactating dairy cows

Objectives were to determine the effects of feeding supplemental 25-hydroxyvitamin D₃ [25(OH)D₃] on concentrations of vitamin D metabolites and minerals in serum, mammary immune status, and responses to intramammary bacterial infection in dairy cows. Sixty multiparous, pregnant lactating Holstein cows with somatic cell count <200,000/mL were blocked by days in milk and milk yield and randomly assigned to receive a daily top-dressed dietary supplement containing 1 or 3 mg of vitamin D₃ (1mgD or 3mgD), or 1 or 3 mg 25(OH)D₃ (1mg25D or 3mg25D) for 28 d (n = 15/treatment). Cows were kept in a freestall barn and fed a total mixed ration in individual feeding gates. Individual dry matter intake (DMI) and milk yield were recorded daily, and milk and blood samples were collected at 0, 7, 14, and 21 d relative to the start of treatment. At 21 d, cows fed 1mgD and 3mg25D received an intramammary challenge with Streptococcus uberis. Cows were observed for severity of mastitis, and blood and milk samples were collected every 12 h to measure inflammation. The 1mg25D and 3mg25D cows had greater serum 25(OH)D₃ concentrations at 21 d compared with 1mgD and 3mgD cows (62 ± 7, 66 ± 8, 135 ± 15, and 232 ± 26 ng/mL for 1mgD, 3mgD, 1mg25D, and 3mg25D, respectively). The 3mg25D cows had greater concentrations of Ca and P in serum at 21 d compared with other treatments (Ca = 2.38, 2.4, 2.37, and 2.48 ± 0.02 mM, 1.87, 1.88, and 2.10 ± 0.08 mM for 1mgD, 3mgD, 1mg25D, and 3mg25D, respectively). Yields of milk and milk components, DMI, body weight, and concentrations of 1,25-dihydroxyvitamin D and Mg in serum did not differ among treatments. Abundance of mRNA transcripts for interleukin-1β (IL1B) and inducible nitric oxide synthase (iNOS) in milk somatic cells before S. uberis challenge were increased in cows fed 25(OH)D₃ compared with cows fed vitamin D₃. Furthermore, IL1B, iNOS, β-defensin 7, and β-defensin 10 in milk somatic cells increased as concentrations of 25(OH)D₃ increased in serum. Cows fed 3mg25D had less severe mastitis at 60 and 72 h after challenge with S. uberis compared with cows fed 1mgD. Concentrations of bacteria, somatic cells, and serum albumin in milk after challenge did not differ between treatments; however, an interaction between treatment and day was detected for lactate dehydrogenase in milk. Expression of adhesion protein CD11b on milk neutrophils after the S. uberis challenge was greater among 3mg25D cows compared with 1mgD cows. Transcripts of CYP24A1 and iNOS in milk somatic cells during mastitis also were greater in 3mg25D cows compared with 1mgD cows. Feeding 25(OH)D₃ increased serum 25(OH)D₃ more effectively than supplemental vitamin D₃, resulting in increased serum mineral concentrations, increased expression of vitamin D-responsive genes, and altered immune responses to intramammary bacterial challenge.

A reduced protein diet modulates enzymes of vitamin D and cholesterol metabolism in young ruminants

Besides other adverse effects, a low protein diet has been shown to modulate cholesterol and vitamin D metabolism in monogastric species like rats and humans. As ruminants can increase the efficiency of the rumino-hepatic circulation of urea, it is assumed that goats should be able to compensate for a low dietary protein intake better. After a dietary protein restriction (9% vs. 20%) for six weeks, plasma concentrations of urea, albumin, 1,25-dihydroxyvitamin D₃ and calcium were decreased, while plasma 25-hydroxyvitamin D₃ (25-OHD₃), and total cholesterol were significantly increased in young goats. Because this was not accompanied by any decrease in expression of CYP24A1 mRNA, we investigated mRNA expression of additional enzymes with known 24- and/or 25-hydroxylase activities (CYP2R1, CYP2J2, CYP3 A24, CYP27A1), receptors involved in their regulation (VDR, PXR, RXRα) and vitamin D binding protein (VDBP). CYP2R1expression was stimulated with the low dietary protein intake, negatively correlated with plasma urea and positively associated with serum 25-OHD₃. The greater plasma concentrations of total cholesterol could be explained with the reduction of CYP2J2 and CYP27A1 expression. None of the receptors investigated were affected by the dietary protein restriction but mRNA expression of VDBP was slightly reduced. Taken together our results show that dietary protein restriction has an impact on vitamin D and cholesterol metabolism in ruminants, too. Therefore, further investigations are needed before dietary interventions aiming at diminishing nitrogen excretion can be implemented.

Gene Mapping and Gene-Set Analysis for Milk Fever Incidence in Holstein Dairy Cattle

Milk fever is an important metabolic disorder that affects dairy cows around parturition. It is associated with a breakdown in the mechanisms of calcium homeostasis, resulting in very low blood calcium levels (hypocalcemia). The main objective of this study was to dissect the genetic basis underlying milk fever incidence in Holstein cattle. Data consisted of 31.6 k producer-recorded lactation incidence records from 15.3 k cows. The analysis included a whole-genome scan and a subsequent gene-set analysis in order to reveal individual genes, genetic mechanisms and biological pathways implicated in the incidence of periparturient hypocalcemia. The association analysis identified at least eight different genomic regions that explain considerable amounts of additive genetic variance for milk fever incidence. Notably, some of these regions harbor genes, such as CYP27A1, CYP2J2, GC, SNAI2, and PIM1, that are directly involved in vitamin D metabolic pathway. Moreover, the gene-set analysis revealed several functional terms, such as calcium ion binding, calcium ion transportation, T cell differentiation, B cell activation, protein phosphorylation, apoptosis, and protein kinase activity, among others, that could be implicated in the development of periparturient hypocalcemia. Overall, this comprehensive study contributes to a better understanding of the genetic control of this complex disease. In addition, these findings may contribute to the development of novel breeding strategies for reducing the incidence of milk fever in dairy cattle.