Immune status during postpartum, peri-implantation and early pregnancy in cattle: An updated view

Vaginitis with purulent vaginal discharge caused by artificial insemination using frozen Histophilus somni-contaminated semen

In April 2020, two cows in Japan, developed reproductive disorders accompanied by vaginitis with purulent discharge within 3 days of artificial insemination (AI) with the same lot of frozen semen. Histophilus somni was isolated from the vaginal swabs of both cows as well as from the same lot of frozen semen used for the AI. This incident marks the first reported case of H. somni infection in cattle through AI. The major outer membrane protein gene sequences and pulsed-field gel electrophoresis profiles of the isolates were identical. Moreover, we investigated the antimicrobial activity of 12 frozen semen straws against an H. somni isolate using a disk diffusion test. These straws were sourced from five AI centers and included the same lot of semen used for the AI. Although the composition of semen diluents from individual AI centers is not publicly available, both the same lot of frozen semen used in the AI and other lots produced by the same manufacturer showed lower antimicrobial activity than semen from other manufacturers. These results strongly suggest that the two vaginitis were caused by AI using H. somni-contaminated frozen semen because of insufficient antimicrobial activity to inhibit bacterial growth. The minimum inhibitory concentrations of the six antimicrobials recommended for addition to frozen semen in isolates were below the recommended concentrations, suggesting that proper addition could have prevented this incident. This highlights the importance of conducting periodical checks on the antibacterial activity of frozen semen to prevent the transmission of pathogens via AI.

β-Hydroxybutyrate affects cell physiological parameters, inflammatory markers and hormone receptor expression in bovine endometrial gland cells in vitro

INTRODUCTION

After calving, dairy cows are commonly affected by negative energy balance (NEB), indicated by high β-Hydroxybutyrate (BHBA) blood levels. These are associated with subfertility frequently related to uterine inflammation. Since this could compromise functionality of endometrial glands that are essential for proper embryo implantation in sheep, we investigated effects of BHBA on bovine endometrial gland cells (BEGC) in vitro.

MATERIAL AND METHODS

BEGC were stimulated with different concentrations of BHBA over different periods. Cell metabolism and motility were examined by MTT-assay and Live-cell-imaging. The mRNA expression of the receptors for estrogen (ESR1, ESR2), progesterone (PR) and IFNτ (IFNAR1, IFNAR2), and the inflammatory cytokines TNFα and IL-6 was determined by RT-qPCR. Protein expression for PR and ESR1 was analyzed by semiquantitative Western Blot.

RESULTS

BEGC metabolism was significantly decreased after stimulation with 1.2, 1.8 and 2.4 mM BHBA over 24 and 36 h. Cell motility was significantly reduced by 1.8 and 2.4 mM BHBA already after 11 h. After 24 h stimulation, the ESR1 mRNA expression was significantly increased in BEGC stimulated with 0.6 mM BHBA. PR and TNFα mRNA expressions were increased in cells stimulated with 2.4 mM BHBA. Protein expression of ESR1 and PR was not altered.

DISCUSSION

Treatment with BHBA leads to restriction of BEGC metabolism and motility, and increased expression of TNFα, ESR1 and PR in vitro. This could explain how increased BHBA blood levels might compromise functionality of uterine glands in vivo and thus could contribute to compromised reproductive success of cows suffering from NEB.

Examination of the haematological profile of pregnant Polish Holstein-Friesian black-and-white cattle in the early stage

Introduction

Cattle health and welfare are monitored via the analysis of the haematological profile, and it shows cattle's ability to adapt to changing environmental conditions, pregnancy and lactation; profile changes also indicate reproductive disorders. The literature lacks reports of the examination of the haematological profile in cows up to the 50th day of pregnancy (dop). Therefore, this research examined that in cows up to this pregnancy stage.

Material and Methods

A total of 101 Polish Holstein-Friesian black-and-white cows were divided into groups. The control groups consisted of non-pregnant heifers (group C00) and non-pregnant cows (group C0), and the experimental groups were pregnant heifers (group T1 at dop ≤ 28 and group T2 at dop ≥ 29-dop < 45) and pregnant cows (group T3 at dop ≥ 29-dop ≤ 50). In addition, the T3 group was divided into cows pregnant for up 45 dop and cows between 45 and 50 dop. Blood samples were collected in March and April 2021 from each animal and analysed. A transrectal ultrasound examination was performed to detect and confirm pregnancy.

Results

Statistically significant differences (P ≤ 0.01) between the group of cows at dop < 45 dop and those at dop ≥ 45-dop ≤ 50 dop were noted in granulocyte percentage (GRA%), white and red blood cell counts (WBC/RBC), platelets (PLT), platelet distribution width (PDW), haematocrit (HCT) and lymphocyte percentage (LYM%). No statistically significant differences were found in the mean corpuscular haemoglobin, monocytes (MON), monocyte percentage (MON%), mean platelet volume (MPV), thrombocrit or red blood cell distribution width (RDW). Similar statistically significant differences (P ≤ 0.01) emerged between the groups of heifers in PLT, GRA, RBC, lymphocytes, LYM% and HCT, and no significant differences were found between MPV, MON, MON% or RDW.

Conclusion

Examining the haematological profile in high-yielding cattle is vital in maintaining herd profitability and high reproduction, which depend on the quick diagnosis of disorders facilitated by haematology. This study analysed the haematology profile of dairy cattle at dop ≤ 50 for the first time, indicating changes in lymphocyte levels, which suggests that the animals experienced direct stress during the study.

Changes in expression of nuclear factor kappa B subunits in the ovine thymus during early pregnancy

There is a pregnant maternal immunological tolerance that protects the fetus and promotes its growth, and nuclear factor kappa B (NF-κB) family participates in the regulation of innate immune and adaptive immune responses. The thymus is related to establishing central tolerance, and early pregnancy has effects on expression of a good number of genes and proteins in the maternal thymus in sheep. However, it is unclear whether early pregnancy changes expression of NF-κB subunits in the ovine thymus. In this study, the thymic samples were collected from day 16 of non-pregnant ewes, and days 13, 16 and 25 of pregnant ewes, and the expression of NF-κB members (NF-κB1, NF-κB2, RelA, RelB and c-Rel) was analyzed through real-time quantitative PCR, Western blot and immunohistochemical analysis. The results showed that c-Rel mRNA and protein upregulated at day 25 of pregnancy, and NF-κB1 mRNA and proteins increased at days 16 and 25 of pregnancy, and RelB mRNA and proteins enhanced during early pregnancy. However, expression levels of NF-κB2 and RelA were decreased during early pregnancy, but upregulated from day 13 to 25 of pregnancy. In addition, the RelA protein was located in the epithelial reticular cells, capillaries and thymic corpuscles. This paper reported for the first time that early pregnancy induced expression of NF-κB1, RelB and c-Rel, but inhibited expression of NF-κB2 and RelA in the maternal thymus during early pregnancy, which is involved in the central immune tolerance, and helpful for successful pregnancy in sheep.

Staphylococcus aureus-Induced Necroptosis Promotes Mitochondrial Damage in Goat Endometrial Epithelial Cells

Simple Summary

The death of endometrial cells induced by bacterial infections can result in damage to the endometrial function. In this study, we investigated the potential role of necroptosis in Staphylococcus aureus-induced goat endometrial epithelial cell (gEEC) death. We found that S. aureus induced gEECs RIPK1/RIPK3/MLKL-mediated necroptosis, triggered mainly by membrane disruption and ion imbalance. Moreover, gEEC necroptosis contributed to the regulation of reactive oxygen species generation and mitochondrial damage. These provide evidence of the involvement of necroptosis in the S. aureus-induced gEEC death.

Abstract

Endometrial cell death is induced by bacterial infection, resulting in damage to the physical barriers and immune function. An in-depth understanding of the mechanisms of endometrial epithelial cell necroptosis might provide new insights into the treatment of uterine diseases. In the present study, we investigated the effect of Staphylococcus aureus on goat endometrial epithelial cell (gEEC) necroptosis, and the underlying molecular mechanism. We found that S. aureus induced significant necroptosis in gEECs by increasing the expression of key proteins of the RIPK1/RIPK3/MLKL axis; importantly, this effect was alleviated by inhibitors of RIPK1, RIPK3, and MLKL. Moreover, we found that the main triggers of gEEC necroptosis induced by S. aureus were not the toll-like receptors (TLRs) and tumor necrosis factor receptor (TNFR), but membrane disruption and ion imbalance. Moreover, we observed a significant decrease in the mitochondrial membrane potential, indicating mitochondrial damage, in addition to increased cytochrome c levels and reactive oxygen species (ROS) generation in S. aureus-infected gEECs; these, effects were also suppressed by the inhibitors of RIPK1, RIPK3, and MLKL. Taken together, these data revealed the molecular mechanism of S. aureus-induced gEEC necroptosis and provided potential new targeted therapies for clinical intervention in bacterial infections.

Staphylococcus aureus Induces Goat Endometrial Epithelial Cells Apoptosis via the Autophagy and Endoplasmic Reticulum Stress Pathway

Simple Summary

The toxicity mechanism of Staphylococcus aureus on goat endometrial epithelial cells (gEECs) is still unelucidated. The purpose of this experiment was to investigate the molecular mechanism of gEECs death caused by S. aureus in terms of autophagy and endoplasmic reticulum (ER) stress. We found that the accumulation of autophagosomes exacerbated S. aureus-induced gEECs apoptosis, and that ER stress was involved in the regulation of the autophagy. These findings may provide new insight into the therapeutic target of endometrial cell injury.

Abstract

Increasing evidence indicates that autophagy and endoplasmic reticulum (ER) stress are involved in the regulation of cell death; however, the role of autophagy and ER stress in Staphylococcus aureus-induced endometrial epithelial cell damage is still unelucidated. In the present study, our results showed that infection with S. aureus increased the cytotoxicity and the protein expression of Bax, caspase-3, and cleaved-PARP-1 in goat endometrial epithelial cells (gEECs). Moreover, after infection, the expression of LC3II and autophagosomes were markedly increased. The autophagosome inhibitor 3-methyladenine (3-MA) significantly decreased the cytotoxicity and the expression of caspase-3, and cleaved-PARP-1; however, the autophagosome–lysosome fusion inhibitor chloroquine (CQ) increased their expression. Additionally, the protein expression of GRP78, EIF2α, and ATF4 were also markedly increased after infection. The ER stress inhibitor 4-PBA decreased the cytotoxicity and the expression of LC3II and apoptosis-related proteins in S. aureus-infected gEECs. Collectively, our findings prove that the accumulation of autophagosomes exacerbated S. aureus-induced gEECs apoptosis, and that ER stress was involved in the regulation of the autophagy and apoptosis.

Major Nutritional Metabolic Alterations Influencing the Reproductive System of Postpartum Dairy Cows

Early successful conception of postpartum dairy cows is crucial in determining the optimum reproductive efficiency and profitability in modern dairy farming. Due to the inherent high production potential of modern dairy cows, the extra stress burden of peri-parturient events, and associated endocrine and metabolic changes causes negative energy balance (NEBAL) in postpartum cows. The occurrence of NEBAL is associated with excessive fat mobilization in the form of non-esterified fatty acids (NEFAs). The phenomenon of NEFA mobilization furthers with occurrence of ketosis and fatty liver in postpartum dairy cows. High NEFAs and ketones are negatively associated with health and reproductive processes. An additional burden of hypocalcemia, ruminal acidosis, and high protein metabolism in postpartum cows presents further consequences for health and reproductive performance of postpartum dairy cows. This review intends to comprehend these major nutritional metabolic alterations, their mechanisms of influence on the reproduction process, and relevant mitigation strategies.

Association between phagocytic activity of monocytes and days to conception after parturition in dairy cows when considering the hormonal and metabolic milieu

The nutritional conditions and immune status of dairy cows affect reproductive performance. This study was conducted with the aim to analyze the phagocytic activity (PA) and phagocytic capacity (PC) of circulating monocytes after the period of transition from pregnancy to lactation, to evaluate possible associations with duration of time period to conception following parturition. Results indicated PA was not associated with duration of time period to conception following parturition. In contrast, cows with a lesser PC conceived earlier (98 ± 9 days in milk, DIM) than those with a greater PC (168 ± 15 DIM). Based on these results, to analyze the association of the hormonal and metabolic milieu with the PA and PC, the animals were grouped considering the days to conception following parturition. In the group with the greater number of days to conception (>168 DIM), the PA was associated with concentrations of progesterone and beta-hydroxybutyrate (BHB) at 90 DIM and glucose at 120 DIM, whereas PC was associated with the concentrations of progesterone, cortisol and glucose at 90 DIM, non-esterified fatty acids (NEFA) at 120 DIM, 17β-estradiol at 150 DIM, and 17β-estradiol and BHB at 180 DIM. Overall, these results represent a new perspective related to the reproductive performance of dairy cows. The modifications of cellular functions may be useful for predicting the onset of health complications in dairy cows and to manage cows in ways that result in an enhanced fertility during the subsequent lactational period.

Conceptus-modulated innate immune function during early pregnancy in ruminants: a review

This review focuses on the innate immune events modulated by conceptus signaling during early pregnancy in ruminants. Interferon-tau (IFN-τ) plays a role in the recognition of pregnancy in ruminants, which involves more than the inhibition of luteolytic pulses of PGF2α to maintain corpus luteum function. For successful pregnancy establishment, the allogenic conceptus needs to prevent rejection by the female. Therefore, IFN-τ exerts paracrine and endocrine actions to regulate the innate immune system and prevent conceptus rejection. Additionally, other immune regulators work in parallel with IFN-τ, such as the pattern recognition receptors (PRR). These receptors are activated during viral and bacterial infections and in early pregnancy, but it remains unknown whether PPR expression and function are controlled by IFN-τ. Therefore, this review focuses on the main components of the innate immune response that are involved with early pregnancy and their importance to avoid conceptus rejection.

Decidual factors and vasoactive intestinal peptide guide monocytes to higher migration, efferocytosis and wound healing in term human pregnancy

AIM

To explore the functional profile of circulating monocytes and decidual macrophages at term human pregnancy and their contribution to tissue repair upon stimulation ex vivo with decidual factors and the vasoactive intestinal peptide (VIP).

METHODS

Peripheral blood monocytes were isolated from pregnant and non-pregnant volunteers and tested in vitro with decidual explants from term placenta and VIP. The effect of VIP on decidual explants and the effect of its conditioned media on monocytes or decidual macrophages isolated by magnetic beads was carried out by RT-qPCR and ELISA for cytokines expression and release. Migration assays were performed in transwell systems. Efferocytosis was assessed in monocytes or decidual macrophages with CFSE-labelled autologous apoptotic neutrophils and quantified by flow cytometry. Monocyte and decidual macrophages wound healing capacity was evaluated using human endometrial stromal cell monolayers. Immunohistochemistry was performed in serial tissue sections of different placentas.

RESULTS

VIP is expressed in the villi as well as in trophoblast giant cells distributed within the decidua of term placenta. VIP induced the expression of antiinflmammatory markers and monocyte chemoattractant CCL2 and CCL3 in decidual tissues. Monocytes presented higher migration towards decidual explants than CD4 and CD8 cells. VIP-conditioned monocytes displayed an enhanced efferocytosis and wound healing capacity comparable to that of decidual macrophages. Moreover limited efferocytosis of pregnant women monocytes was restored by VIP-induced decidual factors.

CONCLUSION

Results show the conditioning of monocytes by decidual factors and VIP to sustain processes required for tissue repair and homeostasis maintenance in term placenta.

Progress and challenges in developing organoids in farm animal species for the study of reproduction and their applications to reproductive biotechnologies

Within the past decades, major progress has been accomplished in isolating germ/stem/pluripotent cells, in refining culture medium and conditions and in establishing 3-dimensional culture systems, towards developing organoids for organs involved in reproduction in mice and to some extent in humans. Haploid male germ cells were generated in vitro from primordial germ cells. So were oocytes, with additional support from ovarian cells and subsequent follicle culture. Going on with the female reproductive tract, spherical oviduct organoids were obtained from adult stem/progenitor cells. Multicellular endometrial structures mimicking functional uterine glands were derived from endometrial cells. Trophoblastic stem cells were induced to form 3-dimensional syncytial-like structures and exhibited invasive properties, a crucial point for placentation. Finally, considering the embryo itself, pluripotent embryonic cells together with additional extra-embryonic cells, could self-organize into a blastoid, and eventually into a post-implantation-like embryo. Most of these accomplishments have yet to be reached in farm animals, but much effort is devoted towards this goal. Here, we review the progress and discuss the specific challenges of developing organoids for the study of reproductive biology in these species. We consider the use of such organoids in basic research to delineate the physiological mechanisms involved at each step of the reproductive process, or to understand how they are altered by environmental factors relevant to animal breeding. We evaluate their potential in reproduction of animals with a high genetic value, from a breeding point of view or in the context of preserving local breeds with limited headcounts.

Local action of cytokines and immune cells in communication between the conceptus and uterus during the critical period of early embryo development, attachment and implantation - Implications for embryo survival in cattle: A review

Early embryo development, implantation and pregnancy involve a complex dialogue between the embryo and mother. In cattle this dialogue starts as early as days 3-4 when the embryo is still in the oviduct, and it continues to implantation. Immunological processes involving cytokines, mast cells and macrophages form an important part of this dialogue. Amongst the cytokines, interleukin-6 (Il-6) and leukemia inhibitory factor (LIF) are secreted by both the embryo and uterine endometrium and form part of an ongoing and reciprocating dialogue. Mast cells and macrophages populate the uterine endometrium during embryo development and are involved in achieving the correct balance between inflammatory and anti-inflammatory reactions at the uterus that are associated with embryo attachment and implantation. Embryo loss is the major cause of reproductive wastage in cattle, and livestock generally. A deeper understanding of immunological processes during early embryo development will help to achieve the next step change in the efficiency of natural and assisted breeding.

Semen extender and seminal plasma alter the extent of neutrophil extracellular traps (NET) formation in cattle

During artificial insemination in bovine, the deposition of semen into the uterus results in an immune reaction which is based on polymorphonuclear neutrophils activity, including the formation of neutrophil extracellular traps. The formation of neutrophil extracellular traps as a reaction of neutrophils to spermatozoa was recently described. However, it is not completely clear which components of the semen are responsible for this reaction. The objective of this study was to quantify and compare the formation of neutrophil extracellular traps following in vitro incubation of bovine polymorphonuclear neutrophils with semen and extenders of different origins and conditions. We investigated the interactions between bovine polymorphonuclear neutrophils and different semen extenders, various seminal plasma concentrations from young and old bulls as well as sexed and non-sexed semen and their corresponding extenders. Three different semen extenders from two companies in fresh and frozen-thawed conditions were compared. Fresh semen extenders showed higher neutrophil extracellular traps induction than did frozen-thawed ones. The formation of neutrophil extracellular traps were also dependent on the presence of seminal plasma. We could show that seminal plasma alone, without any sperm cells, induced the reaction and that the addition of at least 1% seminal plasma already resulted in the formation of neutrophil extracellular traps. Furthermore, seminal plasma from young bulls led to significant higher neutrophil extracellular traps induction. No difference between non-sex-sorted and sex-sorted sperm and its extenders was observed. Taken together, different semen extenders as well as the amount and origin of seminal plasma influence neutrophil extracellular traps formation, whereas sex-sorted sperm did not affect the reaction.

[Bovine uterine diseases: Aspects of microbiology, molecular biology, and immunology]

Postpartum uterine diseases, such as puerperal metritis and clinical endometritis may affect over 40 % of cows in dairy farms. Regardless of their severity, these diseases are one of the main reasons for impaired fertility, causing declines in dairy cow productivity and hence, resulting in economic losses. Although uterine diseases have been the topic of scientific discussion for many years, until now it was not possible to agree on uniform definitions for the different kinds of manifestation. By including technical innovations and testing procedures, enormous scientific progress and a deeper knowledge of the physiology as well as the pathologic mechanisms have been achieved. Bovine metritis and endometritis may be regarded as multifactorial diseases caused by a combination of microbial infection, the dysregulation of the immune system, and additional risk factors. These interactions have been analyzed on microbial and molecular biological levels as well as by the use of bioinformatics and molecular genetics. As a result, new species of bacteria and inflammatory mediators possibly contributing to the development of uterine diseases have recently been described. Additionally, metabolic and genetic risk factors and their roles in leading to fertility impairment have been evaluated. In conclusion, it was possible to identify new approaches for possible therapeutic and preventive methods, a subset of which may already be implemented into daily practical routine. This article provides an overview of recent scientific results concerning bovine metritis and endometritis with a focus on microbial, microbiological and immunological studies.

Period of excretion of equine herpesvirus 3 (EHV-3) from a stallion before showing clinical signs of equine coital exanthema and the effect of acyclovir treatment on the duration of EHV-3 excretion

In 2017, two Thoroughbred stallions, A and B in Farms A and B, respectively, in Hokkaido in Japan showed clinical signs of equine coital exanthema (ECE). In 2020, stallion C in Farm B showed clinical signs of ECE. Eighteen mares were mated within five days before stallion A developed ECE. Ten mares that mated within 3 days before onset showed clinical signs of ECE on the external genitalia. Equine herpesvirus 3 (EHV-3) was isolated from vaginal swabs from three mares that mated within 2 days before onset. Swabs from 12 mares that mated within 4 days before onset were real-time PCR (rPCR)-positive and nine of those mares had an increased EHV-3 antibody titer. The three stallions were administered valaciclovir orally and topical acyclovir ointment was applied. Treatment started on the next day after onset in stallion A and on the day of onset in stallions B and C. EHV-3 was firstly isolated from penis swabs of stallions A and B before treatment and from penis swabs of stallion C 2 days after treatment. EHV-3 was not isolated after 8, 5 and 8 days from onset in stallions A, B and C, respectively. However, swabs were rPCR-positive for at least 12, 9 and 15 days after onset of stallions A, B and C, respectively. EHV-3 was excreted from the stallions at least within 4 days before the onset of ECE, and acyclovir treatment resulted in the termination of excretion within 8 days after onset.

Immunological detection of pregnancy: Evidence for systemic immune modulation during early pregnancy in ruminants

Mammalian pregnancy creates unique challenges for immune systems highly evolved to detect and eliminate invading pathogens. Recognition of the challenges created by gestating a semi-allogeneic fetus evolved from the discipline of transplantation biology and were informed by studies on the unique natural parabiosis that occurs when female calves are gestated with twin male fetuses. These pregnancies typically result in an intersex female termed a freemartin, which revealed insights into development of the male and female reproductive tracts. However, they also uncovered important clues on immune tolerance with wide-ranging implications to reproductive biology, transplantation biology and autoimmune disease. Many studies focused on identifying mechanisms through which the fetus evades maternal immune detection and elimination. These included studies characterizing immune interactions between the fetus and mother at the nourishing interface of the placenta and uterine endometrium. This immunological forbearance only occurs under high concentrations of circulating progesterone. Beyond the requirement for progesterone, there has been considerable progress towards understanding the effects of conceptus signals on maternal immune function. One common theme is that pregnancy induces a T helper 2 immune bias as shown in several mammalian species, including domestic ruminants. However, a growing body of evidence shows that the fetus not only evades, but also provokes immune responses locally in the uterus and in peripheral tissues. This is perhaps most dramatically illustrated by domestic ruminants where the conceptus secretes a unique interferon in the opening salvo of hormonal communication with the maternal immune system. The role of interferon tau in regulating expression of genes of the innate immune system in the uterus has been extensively studied. More recently, it was determined that these same genes are also induced in peripheral immune cells and other tissues throughout the body. In addition to interferon tau and progesterone, pregnancy associate glycoproteins and chaperonin 10 (aka Early Pregnancy Factor) are implicated in altering immune function both locally and systemically during pregnancy. While it is tempting to speculate that this activation of innate immunity is designed to counteract selective immunosuppression, knowledge of the importance of local and systemic immune activation to the success of pregnancy remains incomplete. This area remains fertile ground for developing better approaches to diagnose and treat infertility in domestic farm species and humans alike.

Revisiting Oxidative Stress and the Use of Organic Selenium in Dairy Cow Nutrition

In commercial animals production, productive stress can negatively impact health status and subsequent productive and reproductive performance. A great body of evidence has demonstrated that as a consequence of productive stress, an overproduction of free radicals, disturbance of redox balance/signaling, and oxidative stress were observed. There is a range of antioxidants that can be supplied with animal feed to help build and maintain the antioxidant defense system of the body responsible for prevention of the damaging effects of free radicals and the toxic products of their metabolism. Among feed-derived antioxidants, selenium (Se) was shown to have a special place as an essential part of 25 selenoproteins identified in animals. There is a comprehensive body of research in monogastric species that clearly shows that Se bioavailability within the diet is very much dependent on the form of the element used. Organic Se, in the form of selenomethionine (SeMet), has been reported to be a much more effective Se source when compared with mineral forms such as sodium selenite or selenate. It has been proposed that one of the main advantages of organic Se in pig and poultry nutrition is the non-specific incorporation of SeMet into general body proteins, thus forming an endogenous Se reserve that can be utilized during periods of stress for additional synthesis of selenoproteins. Responses in ruminant species to supplementary Se tend to be much more variable than those reported in monogastric species, and much of this variability may be a consequence of the different fates of Se forms in the rumen following ingestion. It is likely that the reducing conditions found in the rumen are responsible for the markedly lower assimilation of inorganic forms of Se, thus predisposing selenite-fed animals to potential Se inadequacy that may in turn compromise animal health and production. A growing body of evidence demonstrates that organic Se has a number of benefits, particularly in dairy and beef animals; these include improved Se and antioxidant status and better Se transfer via the placenta, colostrum, and milk to the newborn. However, there is a paucity in the data concerning molecular mechanisms of SeMet assimilation, metabolism and selenoprotein synthesis regulation in ruminant animals, and as such, further investigation is required.