Alterations in cortisol concentrations and expression of certain genes associated with neutrophil functions in cows developing retention of fetal membranes

Selenium suppressed the LPS-induced oxidative stress of bovine endometrial stromal cells through Nrf2 pathway with high cortisol background

Stress and infection seriously threaten the reproductive performance and health of dairy cows. Various perinatal stresses increase plasma cortisol concentrations in cows, and chronically high cortisol levels may increase the incidence and severity of the uterine diseases. Selenium (Se) enhances antioxidant capacity of cows. The aim of this study was to explore how Se affects the oxidative stress of primary bovine endometrial stromal cells (BESC) with high cortisol background. The levels of reactive oxygen species (ROS) and other biomarkers of oxidative stress were measured using flow cytometry and assay kits. The changes in nuclear NF-E2-related factor 2 (Nrf2) pathway were detected by Western blot, qPCR, and immunofluorescence. The result showed that lipopolysaccharide (LPS) increased (P < 0.01) ROS and malondialdehyde (MDA) content and reduced (P < 0.01) superoxide dismutase (SOD) concentration, provoking BESC oxidative stress. The elevated levels of cortisol resulted in the accumulation (P < 0.05) of ROS and MDA and inhibition (P < 0.05) of SOD in unstimulated BESC but demonstrated an antioxidative effect in LPS-stimulated cells. Pretreatment with Se reduced (P < 0.01) the levels of ROS and MDA, while increasing (P < 0.05) the antioxidant capacities and the relative abundance of gene transcripts and proteins related to the Nrf2 pathway in BESC. This antioxidant effect was more pronounced in the presence of high cortisol level. In conclusion, cortisol alone induced the oxidative damage but provided an antioxidant protection in the presence of LPS. Se alleviated the LPS-induced cellular oxidative stress, which is probably achieved through activating Nrf2 pathway. At high cortisol levels, Se supplement has a more significant protective effect on BESC oxidative stress. This study provided evidence for the protective role of Se in bovine endometrial oxidative damage of stressed animals and suggested the potential regulatory mechanism in vitro.

Selenium suppressed the LPS-induced inflammation of bovine endometrial epithelial cells through NF-κB and MAPK pathways under high cortisol background

The bovine uterus is susceptible to infection, and the elevated cortisol level due to stress are common in cows after delivery. The essential trace element selenium plays a pivotal role in the antioxidant and anti-inflammatory defence system of body. This study investigated whether selenium supplementation protected endometrial cells from inflammation in the presence of high-level cortisol. The primary bovine endometrial epithelial cells were subjected to Escherichia coli lipopolysaccharide to establish cellular inflammation model. The gene expression of inflammatory mediators and proinflammatory cytokines was measured by quantitative PCR. The key proteins of NF-κB and MAPK signalling pathways were detected by Western blot and immunofluorescence. The result showed that pre-treatment of Na2 SeO3 (1, 2 and 4 μΜ) decreased the mRNA expression of proinflammatory genes, inhibited the activation of NF-κB and suppressed the phosphorylation of extracellular signal-regulated kinase, P38MAPK and c-Jun N-terminal kinase. This inhibition of inflammation was more apparent in the presence of high-level cortisol (30 ng/mL). These results indicated that selenium has an anti-inflammatory effect, which is mediated via NF-κB and MAPK signalling pathways and is augmented by cortisol in bovine endometrial epithelial cells.

Repeated injection of multivitamins and multiminerals during the transition period enhances immune response by suppressing inflammation and oxidative stress in cows and their calves

Periparturient dairy cows undergo major physiological and metabolic changes as well as immunosuppression, associated with decrease in plasma concentrations of various minerals and vitamins. The present study was conducted to investigate effects of repeated injections of vitamins and minerals on oxidative stress, innate and adaptive immune response in periparturient dairy cows and their offspring. Experiment was carried out on 24 peripartum Karan-Fries cows, randomly divided into four groups (n=6): control, Multi-mineral (MM), Multi-vitamin (MV) and Multi-minerals and Multi-vitamin (MMMV). Five ml of MM (Zinc 40 mg/ml, Manganese 10 mg/ml, Copper 15 mg/ml, Selenium 5 mg/ml) and five ml of MV (Vitamin E 5 mg/ml, Vitamin A 1000 IU/ml, B-Complex 5 mg/ml, and Vitamin D₃ 500 IU/ml) were injected intramuscularly (IM) to the MM and MV groups. MMMV group cows were injected with both. In all treatment groups, injections and blood sampling were carried out on 30^th, 15^th, 7^th days before and after expected date of parturition and at calving. In calves, blood was collected at calving and on 1, 2, 3, 4, 7, 8, 15, 30 and 45 days post-calving. Colostrum/milk were collected at calving and at days 2, 4, and 8 post-calving. A lower percentage of total neutrophils and immature neutrophils, higher percentage of lymphocytes together with increased phagocytic activity of neutrophils and proliferative capacity of lymphocytes found in blood of MMMV cows/calves. Lower relative mRNA expression of TLRs and CXCRs and higher mRNA expression of GR-α, CD62L, CD11b, CD25 and CD44 found in blood neutrophils of MMMV groups. Total antioxidant capacity was higher, activity of antioxidant enzymes (SOD and CAT), TBARS levels were lower in the blood plasma of treated cows/calves. In both cows/calves, plasma pro-inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-8, IL-17A, IFN-γ and TNF-α) increased, whereas anti-inflammatory cytokines (IL-4 and IL-10) decreased in MMMV groups. Total immunoglobulins increased in colostrum/milk of MMMV injected cows and plasma of their calves. Results indicate that repeated injections of multivitamins and multiminerals to peripartum dairy cows could be a major strategy to improve immune response and decrease in inflammation and oxidative stress in transition dairy cows and their calves.

Effect of 6‐n‐propyl‐2‐thiouracil or dexamethasone administration on the responses of antimicrobial components in goat milk to intramammary lipopolysaccharide infusion

Heat stress impacts the immune system of dairy animals by altering the hypothalamic-pituitary-adrenal axis and thyroid function, leading to conditions such as hypothyroidism and hypercortisolism. This study aimed to elucidate the effect of hypothyroidism and hypercortisolism on the response of mammary innate immune function to inflammation caused by Escherichia coli in dairy goats. To induce hypothyroidism and hypercortisolism, we administered 6-n-propyl-2-thiouracil (PTU; for 21 days) and dexamethasone (DEX; for 5 days), respectively, to six goats each; six goats without treatment were used as the control group. After treatment, lipopolysaccharide (LPS) from E. coli O111 was infused into the mammary gland. Somatic cell counts (SCC) and levels of lactoferrin (LF), S100A7, immunoglobulin A (IgA), and interleukin-8 (IL-8) in milk until 7 days after LPS infusion were measured. An increase in SCC after LPS infusion was inhibited in both PTU and DEX groups, and an increase in LF after LPS infusion was inhibited in PTU group, compared with that in the control group. The results of the present study suggest that the recruitment of neutrophils and LF production decreased under hypothyroidism or hypercortisolism, which may be one of the causes underlying increased incidence of mastitis in dairy animals under heat stress conditions.

Supplementation of a combination of herbs improves immunity, uterine cleansing and facilitate early resumption of ovarian cyclicity: A study on post-partum dairy buffaloes

ETHNOPHARMACOLOGICAL RELEVANCE

A combination of Trachyspermum ammi L., Curcuma longa L., Cuminum cyminum L., Trigonella foenum-graecum L., Foeniculum vulgare Mill., Anethum graveolens L and Zingiber officinale Roscoe is used as immunity booster and reproductive efficiency enhancing agents in folklore medicine.

AIM OF THE STUDY

The present study aimed to assess the immunomodulatory, uterine cleansing and reproduction enhancing effects of polyherbal mixture in post-partum buffaloes.

MATERIALS AND METHODS

Enzyme linked immunosorbent assay (ELISA) was used to investigate the effects of polyherbal mixture feeding on for quantification of neutrophil functions and blood progesterone hormone estimation. Ultrasonography was used to assess the status of uterine involution, fluid in uterus and ovarian follicular status. Quantitative real time PCR (qRT-PCR) was used to measure the expression of chemokine genes CXCR1, CXCR2 AND IL-8. Artificial insemination with cryopreserved semen was used to breed the animals. Reproductive efficiency parameters were assessed using standard calculation methods.

RESULTS

Neutrophil functions and transcriptional abundance of chemokine genes were significantly (P < 0.05) higher in buffaloes supplemented with polyherbal mixture compared to buffaloes in control group. The rate of cervical and uterine involution was significantly (P < 0.05) higher in treatment group compared to control group. The service period was shorter, days to first insemination was earlier and the number of services per conception was lower in buffaloes supplemented with polyherbal mixture compared to the buffaloes in control group. The proportion of buffaloes with large ovarian follicles within 28 days of post-partum was also significantly (P < 0.05) higher in treatment group compared to the control group.

CONCLUSIONS

The polyherbal mixture used in the study improved the immunity of the buffaloes, facilitated early involution of cervix and uterus, efficient cleansing of lochia and improved subsequent fertility. It has the potential to be used in dairy animals for improving post-partum reproductive efficiency.

Supplementation of antioxidant micronutrients reduces stress and improves immune function/response in periparturient dairy cows and their calves

BACKGROUND

Periparturient period induces stress in cows which fluctuates hormonal and metabolic function and causes immune suppression. Apart from impairing the health, production, and reproduction of cows, it also influences the well-being of newborn calves by decreasing the colostrum quality. Micronutrients are known for optimal health and production and their effects on parturition stress, immune response in both cow and its calf need to be explored.

AIM

The aim of this study was to see the effect of oral supplementation of micronutrients during the prepartum period on the health status of crossbred dairy cows and subsequently on their newborn calves.

METHODS

A total of 42 healthy multiparous cows were selected and randomly divided into five groups with seven cows in each group, i.e. control (Basal Diet, BD), VA group (BD + vitamin A, 10⁵ IU), Zn group (BD + zinc sulphate, 60 ppm), VE group (BD + vitamin E, 2500 IU), and combined supplementation (CS) group (BD + combination of VA, Zn, and VE). The supplements were offered in compounded concentrate DM (100 g) to individual cows once daily before the morning feeding and the remaining portion was incorporated in the TMR. Feeding was started one month before the expected days of calving till calving. Blood samples were collected from cows at days -15, -7, -3, 0, +3, +7, and +15 relative to the day of calving. Blood samples from newborn calves and milk samples of cows were collected at days 0, +3, +7, and +15. Milk somatic cell counts (SCC) were estimated using a cell counter. Cortisol was estimated by ELISA kit in blood and milk plasma of cows and in the blood plasma of their calves. Total immunoglobulins (Ig) were estimated in milk of cows and serum of calves using zinc sulphate turbidity method. Blood neutrophils from cows and calves were studied for phagocytic activity (PA) using nitro blue tetrazolium (NBT) assay.Data were analysed by repeated-measures two-way ANOVA using the mixed procedure of SAS, and the pairwise comparison was performed using a multiple comparison test (Tukey).

RESULTS

Combined supplementation of micronutrients decreased (P < 0.05) maternal blood plasma (control vs. CS group, 5.98 ± 0.20 vs. 3.86 ± 0.23 ng/mL) and milk plasma (3.96 ± 0.13 vs. 2.71 ± 0.10 ng/mL) cortisol, milk SCC (3.05 ± 0.11 vs. 2.12 ± 0.10 × 10⁵ cells/mL) and increased (P < 0.05) total milk Ig concentration (18.80 ± 0.11 vs. 23.04 ± 0.57 mg/mL) and the PA of blood neutrophils (0.84 ± 0.03 vs. 1.07 ± 0.03). Similarly, lower blood cortisol concentration (9.69 ± 0.35 vs. 6.02 ± 0.18 ng/mL) and higher (P < 0.05) total Ig (23.26 ± 0.11 vs. 30.34 ± 0.70 mg/mL) and PA of blood neutrophils (0.37 ± 0.02 vs. 0.52 ± 0.02) were observed in the calves born to CS group of cows as compared to the control. Highest (P < 0.05) positive effects (lower stress levels and higher immune response) of treatment were noticed in CS group followed by VE group and then Zn group. However, VA group didn't differ from the control group.

CONCLUSION

Our results indicate that micronutrient interventions during the prepartum period can improve the health status of dairy calves and subsequently the well-being of their calves.

NETosis of Peripheral Neutrophils Isolated From Dairy Cows Fed Olive Pomace

Neutrophils represent primary mobile phagocytes recruited to the site of infection, and their functions are essential to enhance animals' health performance. Neutrophils have an essential role in innate immunity and are able to kill the pathogens via the synthesis of neutrophil extracellular traps (NETs). The objective of the present work was the study of the in vitro NETosis of peripheral neutrophils isolated from dairy cows supplemented with olive pomace. Dairy cows (n = 16) balanced for parity (3.67 ± 1.5 for CON, 3.67 ± 1.9 for OP), milk yield (24.3 ± 4.5 kg d⁻¹for CON and 24.9 ± 1.7 kg d⁻¹ for OP), the number of days in milk (109 ± 83.5 for CON and 196 ± 51 for OP), and body weight (647 ± 44.3 kg for CON and 675 ± 70.7 kg for OP) were divided into two experimental groups fed with a control diet (CON) and supplemented with 6% of olive pomace (OP). Peripheral blood neutrophils were isolated and stimulated in vitro with phorbol-myristate-acetate (PMA) as a marker for activation and reactivity of the neutrophils. After isolation, both the viability and CD11b expression were analyzed by flow cytometry. Both NETosis by neutrophil elastase-DNA complex system and myeloperoxidase (MPO) activity were evaluated by ELISA. The specific antibodies against MPO and citrullination of Histone-H1 were used for investigating NETosis by immunofluorescence microscopy. The neutrophil elastase-DNA complexes produced during NETosis and MPO activity of neutrophil extracts were affected by OP supplementation. Furthermore, results from immunofluorescence analysis of NETosis depicted a similar result found by ELISA showing a higher expression of MPO and citrullination of Histone-H1 in OP than the CON neutrophils. In addition, all data showed that the OP diet resulted in a better response of neutrophils to PMA stimulation than the CON diet, which did not support the neutrophils' responses to PMA stimulation. Our results demonstrated that OP supplementation can enhance the neutrophil function in dairy cows leading to udder defense and inflammation response especially when an immunosuppression state can occur.

Peripartum changes in the activity and expression of neutrophils may predispose to the postpartum occurrence of metritis in dairy cows

Metritis is a postpartum uterine pathology that causes a huge economic loss due to increased culling risk and impaired milk yield and reproduction in cows. The present study was carried out to study the changes in the activity and expression of blood neutrophils in crossbred dairy cows with and without metritis. Collection of blood samples was done at -3, -2 and - 1 weeks before calving, at calving and during the first day of metritis diagnosis in metritis group (n = 8) or at day 8-10 post calving in healthy group (n = 8). Neutrophils were studied for its percentage (microscopically), respiratory burst (nitro blue tetrazolium assay), myeloperoxidase (MPO) concentrations (sandwich ELISA) and expression of CXCR1, CXCR2, TLR2, TLR4, GRα, CD11b, CD14, CD25, CD44, CD47 and CD62L (RT-PCR). Immunocytochemistry was used to investigate MPO concentration and CD14 activity, and western blotting was used for estimating MPO. Although most of these parameters changed in the cows that developed metritis one week before calving, MPO and CD14 got altered much earlier. Myeloperoxidase concentrations and expression of CD14 were considerably lower starting from -2 weeks before calving in cows that developed metritis compared to healthy cows. Further studies are warranted to study the possible use of MPO and CD14 to identify transition cows more vulnerable to develop metritis several weeks before disease occurrence.

Association of peripartum progesterone, estradiol, cortisol, PGFM and relaxin concentrations with retention of fetal membranes in crossbred dairy cows

Retention of fetal membranes (RFM) in bovines not only lowers fertility and productivity but also leads to significant economic loss to the dairy farms. The present study compared peripartum progesterone, estradiol, cortisol, Prostaglandin F2 metabolite (PGFM) and relaxin concentrations in crossbred cows with normal parturition (NP) and with RFM. Blood samples were collected from 33 dairy cows at weekly interval from 30 days prepartum till 7th day before calving, followed by every alternate days till calving and 1st and 2nd day postpartum. Significantly higher plasma cortisol concentrations was observed between day 3 prepartum and day 2 postpartum in RFM cows (n=6) compared to NP cows (n=6). Plasma estradiol level was significantly lower in RFM group than in NP group on the day of calving while progesterone concentrations did not differ between the groups. In RFM cows, PGFM level was significantly lower on day 1 and day 2 postpartum compared to NP cows. On the day of calving and on day 1 postpartum, relaxin concentration was significantly (P<0.05) higher in NP cows compared to RFM cows. The ROC analysis, commonly used for development of diagnostic threshold value, revealed that cows with cortisol concentration above 7.35 ng/ml and PGFM concentration below 1,072 pg/ml on day-1 were associated with 5.99 times higher risk of RFM. It may be inferred that peripartum plasma cortisol and PGFM concentrations may be useful for identification of crossbred cows at the risk of developing RFM.

Interaction between stress hormones and phagocytic cells and its effect on the health status of dairy cows: A review

Dairy cows are exposed to various stressors during their production cycle that makes them more susceptible to various diseases. Phagocytes (neutrophils and macrophages) are important soldiers of the innate immune system. Neutrophils are the first responders to an inflammatory response and stress and kill pathogens by generating reactive oxygen species and by the release of various antimicrobial peptides, enzymes, neutrophil extracellular trap formation, etc. Macrophages, the other phagocytes, are also the cleanup crew for the innate immune system that removes debris, pathogens, and dead neutrophils later on after an inflammatory response. The neuroendocrine system along with phagocytes exhibits an immunomodulatory potential during stressful conditions. Neuroendocrine system directly affects the activity of phagocytes by communicating bidirectionally through shared receptors and messenger molecules such as hormones, neurotransmitters, or cytokines. Different immune cells may show variable responses to each hormone. Short time exposure to stress can be beneficial, but repeated or extended exposure to stress may be detrimental to the overall health and well-being of an animal. Although some stresses associated with farming practices in dairy cows are unavoidable, better understanding of the interactions occurring between various stress hormones and phagocytic cells can help to reduce stress, improve productivity and animal welfare. This review highlights the role played by various stress hormones in modulating phagocytic cell performance of dairy cattle under inflammatory conditions.

Potential roles of neutrophils in maintaining the health and productivity of dairy cows during various physiological and physiopathological conditions: a review

Neutrophils represent the first line of innate immunity and are the most prominent line of cellular defence against invading microorganisms. On stimulation, they can quickly move through the walls of veins and into the tissues of the body to immediately attack or monitor the foreign antigens. Neutrophils are highly versatile and sophisticated cells which are endowed with highly sensitive receptor-based perception systems. They were traditionally classified as short-lived phagocytes actively involved during infection and inflammation, but recently, it has been seen that neutrophils are capable of detecting the presence of sperms during insemination as well as an implanting embryo in the female reproductive tract. These specialised phagocytes play a major role in tissue remodelling and wound healing, and maintain homeostasis during parturition, expulsion of placenta, folliculogenesis, corpus luteum formation and luteolysis. Here, we review the role played by neutrophils in maintaining homeostasis during normal and inflammatory conditions of dairy cattle. We have summarised the alteration in the expression of some cell adhesion molecules and cytokines on bovine neutrophils during different physiological and physiopathological conditions. Some emerging issues in the field of neutrophil biology and the possible strategies to strengthen their activity during the period of immunosuppression have also been discussed.

Evaluation of infrared thermography compared to rectal temperature to identify illness in early postpartum dairy cows

This study evaluated and compared infrared thermography (IRT) and rectal temperature (RT) as screening tests to identify sick transition dairy cows. Holstein cows (n = 72; 42 primiparous) had RT and IRT temperatures taken daily from 1 to 12 days in milk (DIM). Health examinations were performed daily to diagnose retained fetal membrane, milk fever and metritis, and blood was analyzed for β-hydroxybutyrate at 6 and 9 DIM to diagnose ketosis. Plasma concentrations of cortisol, interleukin-6, tumor necrosis factor α and serum amyloid A at 3, 6, 9 and 12 DIM were included as additional indicators of illness. Cows were categorized as true sick if clinically diagnosed with an illness, or if at least 2 blood parameters were above the normal range. Diagnostic test performances for RT and IRT variables were determined for each variable at a test referent value that provided the highest Youden's (J) index. The best performing screening test depended on the definition of true sickness. In general, the J index for RT was 0.15-0.17 whereas the highest J index for the IRT variables was 0.22 for the mean eye temperature and 0.19 for the mean cheek temperature. Infrared thermography was at least comparable to RT and some IRT variables performed better as a screening tests than RT. Future studies into the automation of IRT for surveillance of early postpartum diseases is warranted.

Pathogen-dependent modulation of milk neutrophils competence, plasma inflammatory cytokines and milk quality during intramammary infection of Sahiwal (Bos indicus) cows

The aim of the current study was to investigate the responses of milk neutrophils and plasma inflammatory cytokines to various mastitis pathogens and subsequently on milk composition. Milk was collected from healthy (n = 10) and clinical mastitis indigenous Sahiwal cows naturally infected either with gram-positive bacteria mainly S. aureus (n = 10) and Strep. agalactiae (n = 10) or with gram-negative bacteria, E. coli (n = 10). Phagocytic activity of milk neutrophils decreased in all mastitis cows with the lowest values recorded during gram-positive bacterial infections. Maximum plasma cortisol levels were observed in cows infected with gram-positive bacteria and were positively correlated with the milk neutrophils percentage and negatively correlated with the phagocytic activity of neutrophils and expression of glucocorticoid receptor. The plasma concentrations of IL-2 and IL-8 increased in all mastitis groups with maximum values recorded during E. coli infections. Unlike gram-negative bacterial infections, gram-positive bacterial infections evoked a minimal tumor necrosis factor-α (TNF-α), and IL-6 response. Milk somatic cell counts, fat, protein, pH and electrical conductivity increased in mastitis cows with the highest values exhibited by Strep. agalactiae infection. The expression of chemokine receptors (CXCR1, CXCR2), IL-8 and CD11b was maximum in mastitis neutrophils infected with E. coli. The expression of glucocorticoid receptor (GRα) decreased in all mastitis groups with the lowest values were found in S. aureus infection. Among the various mastitis pathogens, Strep. agalactiae showed maximum adverse effect on milk quality. Attenuated neutrophils, TNF-α and IL-6 response in cows infected by gram-positive bacteria may contribute to the establishment of chronic mastitis.

Cortisol modulates inflammatory responses in LPS-stimulated RAW264.7 cells via the NF-κB and MAPK pathways

Background

The uteruses of most dairy cattle are easily infected by bacteria, especially gram-negative bacteria, following parturition. Macrophages are important cells of the immune system and play a critical role in the inflammatory response. In addition, cortisol levels become significantly increased due to the stress of parturition in dairy cattle, and cortisol is among the most widely used and effective therapies for many inflammatory diseases. In this study, we assessed the anti-inflammatory effects and potential molecular mechanisms of cortisol using a Lipopolysaccharide (LPS)-induced RAW264.7 macrophage cell line.

Results

Cortisol significantly suppressed the production of prostaglandin E₂ (PGE₂) and decreased the gene and protein expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in a dose-dependent manner. Moreover, cortisol inhibited the mRNA expression of pro-inflammatory cytokines including tumor necrosis factor alpha (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6) and decreased IL-1β secretion in an LPS-treated RAW264.7 macrophage cell line. Moreover, we found that cortisol suppressed nuclear factor-kappa B (NF-κB) signaling in RAW264.7 macrophages stimulated with LPS. This suppression was mediated by the inhibition of IκBα degradation and NF-κB p65 phosphorylation. In addition, cortisol also suppressed the phosphorylation of mitogen-activated protein kinases (MAPK) such as extracellular signal-regulated kinase (ERK1/2), p38 MAPK, and c-Jun N-terminal kinase/stress-activated protein kinase (JNK).

Conclusions

These results suggest that high cortisol levels can attenuate LPS-induced inflammatory responses in the RAW264.7 macrophage cell line by regulating the NF-κB and MAPK signaling pathways.

Cellular and molecular mechanisms involved in placental separation in the bovine: A review

Retention of fetal membranes (RFM), where the fetal placenta is not expelled within 8-12 hr after calving, lowers bovine productivity and fertility, resulting in significant economic loss to the dairy industry. Several risk factors that predispose an individual to RFM are known, but a unifying pathogenesis remains elusive due to its multifactorial etiology. Fetal membrane separation and expulsion after parturition involves structural and immunological changes of the bovine placentome that are governed predominantly by steroid hormones and the prostaglandin milieu of late pregnancy and parturition. Maturation of the placentome, a gradual and concerted event of late gestation, is likely initiated by the up-regulation of fetal major histocompatibility complex class I in the interplacentomal region-which increases the apoptosis of binucleate and other trophoblastic cells, the degradation of collagen in the extracellular matrix by matrix metalloproteinases, and an influx of phagocytic leukocytes. Shear force further distorts the crypt architecture of the mature placentomes when they are forced against the fetus during the second stage of labor. Cotyledon dehiscence from the caruncular crypts is completed following fetal expulsion as a result of acute shrinkage of the cotelydonary villi as well as reduced perfusion to the caruncle; the secundinae is expelled by uterine contractions. A better understanding of placentomal maturation, intra-partum, and immediate postpartum changes of the placentome should help develop strategies for the treatment and prevention of RFM. The present review proposes a model of placentome maturation and separation of fetal membranes in the dairy cow.