Hormones, mammary growth, and lactation: a 41-year perspective

Post-lactation mass recovery and metabolic hormone dynamics in adult female Weddell seals

Weddell seal (Leptonychotes weddellii) females lose substantial body mass across an intensive, nutritionally restricted lactation period and then must rapidly recover mass during the short Antarctic summer. In this study, we examined endocrine dynamics associated with mass loss across lactation and subsequent realimentation in Weddell seals, comparing patterns between seals that recently gave birth and demographically similar non-reproductive females (skip females) in McMurdo Sound, Antarctica. Postpartum seals near weaning (∼35 days postpartum, n = 64) and skip females (n = 32) were handled during early austral summer (November/December) and rehandled in late summer (January/February). Body mass, body composition (% lipid), and a suite of metabolic hormones (growth hormone (GH), insulin-like growth factor (IGF)-I, cortisol, total thyroxine (tT4), free thyroxine (fT4), and total triiodothyronine (tT3) and IGF binding protein (IGFBP)-2 and -3) were measured. Postpartum seals gained mass after weaning (0.98 ± 0.56 kg·day-1 (mean ± SD)), primarily as lean tissue rather than lipid, while their serum concentrations of tT4 and fT4, IGF-I, and cortisol increased. Their circulating GH and IGFBP-2 concentrations decreased and correlated negatively with mass. Skip females had greater body masses and lipid stores than postpartum seals at the end of the lactation period in early summer, but they lost mass (-1.03 ± 0.35 kg·day-1) and lipid stores over summer while their serum cortisol concentrations increased. Overall, body mass and composition of postpartum and skip females converged across summer. This convergence, likely driven in large part by contrasting endocrine profiles between the groups, may allow female Weddell seals to reach an advantageous seasonal body mass "set point" by onset of winter.

The effects of anti-galactagogue (sage, parsley extract) and anti-inflammatory (echinacea extract) feed supplements on prolactin levels and fertility in the re-pregnancy of lactating Merino ewes

The purpose of this study was to examine the effects of anti-galactagogue (sage, parsley extract) and anti-inflammatory (echinacea extract) feed supplements on prolactin levels and fertility in the re-pregnancy of lactating Merino ewes. Eighty ewes were randomly assigned to one of two groups: control and treatment. In treatment group (Stop Lactin) group (n = 40) ewes were treated with Stop Lactin® 60 ml on day 0 orally by syringe. The control group (Control) (n = 40), ewes were not treated with any anti-galactagogue feed supplements. On day 0, a vaginal sponge containing 60 mg of medroxyprogesterone acetate was inserted for seven days. On day 7, all ewes received an intramuscular injection of 500 IU PMSG. The study results indicated no statistically significant differences between the Control group and Stop Lactin group in terms of conception rates (87.2% and 78.1%), late embryonic-early fetal mortality rate (20.6% and 8.0%), lambing rate (79.4% and 92%), twin rate (29.6% and 13.0%) and litter size (1.30 and 1.13). Estrus rates (97.5% and 82.1%, p = 0.050) tended to be higher and pregnancy rates (85.0% and 64.1%, p = 0.037) was found to be significant in the control group compared to the Stop Lactin group. The effect of treatment (P = 0.209) on serum prolactin levels and the interaction between treatment × day (P = 0.874) were both found to be insignificant. It is concluded that anti-galactagogue and anti-inflammatory feed supplements did not reduce prolactin concentration and did not improve fertility in lactating Merino ewes.

The role of hormones in the regulation of lactogenic immunity in porcine and bovine species

Colostrum and milk offer a complete diet and vital immune protection for newborn mammals with developing immune systems. High immunoglobulin levels in colostrum serve as the primary antibody source for newborn piglets and calves. Subsequent milk feeding support continued local antibody protection against enteric pathogens, as well as maturation of the developing immune system and provide nutrients for newborn growth. Mammals have evolved hormonal strategies that modulate the levels of immunoglobulins in colostrum and milk to facilitate effective lactational immunity. In addition, hormones regulate the gut-mammary gland-secretory immunoglobulin A (sIgA) axis in pregnant mammals, controlling the levels of sIgA in milk, which serves as the primary source of IgA for piglets and helps them resist pathogens such as PEDV and TGEV. In the present study, we review the existing studies on the interactions between hormones and the gut-mammary-sIgA axis/lactogenic immunity in mammals and explore the potential mechanisms of hormonal regulation that have not been studied in detail, to draw attention to the role of hormones in influencing the immune response of pregnant and lactating mammals and their offspring, and highlight the effect of hormones in regulating sIgA-mediated anti-infection processes in colostrum and milk. Discussion of the relationship between hormones and lactogenic immunity may lead to a better way of improving lactogenic immunity by determining a better injection time and developing new vaccines.

Chronic Stress Decreases Lactation Performance

The ability to provision offspring with milk is a significant adaptive feature of mammals that allows for considerable maternal regulation of offspring beyond gestation, as milk provides complete nutrition for developing neonates. For mothers, lactation is a period of marked increases in energetic and nutritive demands to support milk synthesis; because of this considerable increase in demand imposed on multiple physiological systems, lactation is particularly susceptible to the effects of chronic stress. Here, we present work that explores the impact of chronic stress during lactation on maternal lactation performance (i.e., milk quality and quantity) and the expression of key milk synthesis genes in mammary tissue using a Sprague-Dawley rat model. We induced chronic stress using a well-established, ethologically relevant novel male intruder paradigm for 10 consecutive days during the postpartum period. We hypothesized that the increased energetic burden of mounting a chronic stress response during lactation would decrease lactation performance. Specifically, we predicted that chronic exposure to this social stressor would decrease either milk quality (i.e., composition of proximate components and energy density) or quantity. We also predicted that changes in proximate composition (i.e., lipid, lactose, and protein concentrations) would be associated with changes in gene expression levels of milk synthesis genes. Our results supported our hypothesis that chronic stress impairs lactation performance. Relative to the controls, chronically stressed rats had lower milk yields. We also found that milk quality was decreased; milk from chronically stressed mothers had lower lipid concentration and lower energy density, though protein and lactose concentrations were not different between treatment groups. Although there was a change in proximate composition, chronic stress did not impact mammary gland expression of key milk synthesis genes. Together, this work demonstrates that exposure to a chronic stressor impacts lactation performance, which in turn has the potential to impact offspring development via maternal effects.

Oestrogens and progesterone in human milk and their effects on infant health outcomes: A narrative review

Human milk (HM) is a complex biological system that contains a wide range of bioactive components including oestrogens and progesterone. Whilst maternal oestrogens and progesterone concentrations drop rapidly after birth, they remain detectable in HM across lactation. Phytoestrogens and mycoestrogens, which are produced by plants and fungi, are also present in HM and can interact with oestrogen receptors to interfere with normal hormone functions. Despite the potential impact of HM oestrogens and progesterone on the infant, limited research has addressed their impact on the growth and health of breastfed infants. Furthermore, it is important to comprehensively understand the factors that contribute to these hormone levels in HM, in order to establish effective intervention strategies. In this review, we have summarized the concentrations of naturally occurring oestrogens and progesterone in HM from both endogenous and exogenous sources and discussed both maternal factors impacting HM levels and relationships with infant growth.

Symposium review: The impact of absorbed nutrients on energy partitioning throughout lactation

Most nutrition models and some nutritionists view ration formulation as accounting transactions to match nutrient supplies with nutrient requirements. However, diet and stage of lactation interact to alter the partitioning of nutrients toward milk and body reserves, which, in turn, alters requirements. Fermentation and digestion of diet components determine feeding behavior and the temporal pattern and profile of absorbed nutrients. The pattern and profile, in turn, alter hormonal signals, tissue responsiveness to hormones, and mammary metabolism to affect milk synthesis and energy partitioning differently depending on the physiological state of the cow. In the fresh period (first 2 to 3 wk postpartum), plasma insulin concentration and insulin sensitivity of tissues are low, so absorbed nutrients and body reserves are partitioned toward milk synthesis. As lactation progresses, insulin secretion and sensitivity increase, favoring deposition instead of mobilization of body reserves. High-starch diets increase ruminal propionate production, the flow of gluconeogenic precursors to the liver, and blood insulin concentrations. During early lactation, the glucose produced will preferentially be used by the mammary gland for milk production. As lactation progresses and milk yield decreases, glucose will increasingly stimulate repletion of body reserves. Diets with less starch and more digestible fiber increase ruminal production of acetate relative to propionate and, because acetate is less insulinogenic than propionate, these diets can minimize body weight gain. High dietary starch concentration and fermentability can also induce milk fat depression by increasing the production of biohydrogenation intermediates that inhibit milk fat synthesis and thus favor energy partitioning away from the mammary gland. Supplemental fatty acids also impact energy partitioning by affecting insulin concentration and insulin sensitivity of tissues. Depending on profile, physiological state, and interactions with other nutrients, supplemental fatty acids might increase milk yield at the expense of body reserves or partition energy to body reserves at the expense of milk yield. Supplemental protein or AA also can increase milk production but there is little evidence that dietary protein directly alters whole-body partitioning. Understanding the biology of these interactions can help nutritionists better formulate diets for cows at various stages of lactation.

Hormonal and immunological responses of Holstein dairy cows from late lactation to the dry period and from the dry period to early lactation

Parturition and dry-off are challenging events for dairy cows partially due to changes in endocrine responses. The aim of this experiment was to evaluate blood concentrations of cortisol and prolactin and their effects on proliferation of peripheral blood mononuclear cells (PBMC) with or without stimulation by common immune cell mitogens (lipopolysaccharide [LPS], and concanavalin A [ConA]) of multiparous dairy cows from late lactation to the dry period and from the dry period to early lactation. Two groups of cows were enrolled: cows from late lactation to the dry period enrolled at 8 d before dry-off (LTD, n = 6, days in milk at dry-off = 332 ± 41 d) and cows from the dry period to early lactation enrolled at 7 d before expected calving date (DTL, n = 7). Blood was collected on d -8, 3, 7, and 15 relatives to dry-off for LTD cows, and on d -7, 3, 7, and 21 relatives to calving for DTL cows to analyze circulating stress hormones and to isolate PBMC. The PBMC were stimulated in vitro with prolactin (PRL), hydrocortisone (HDC), LPS, ConA, PRL + LPS, PRL + ConA, HDC+LPS, and HDC + ConA to assess proliferative responses. Plasma cortisol and PRL concentrations of LTD and DTL cows were not affected by time. Regardless of time, addition of HDC reduced PBMC proliferation stimulated by LPS, but PRL had no effect. No time effect was observed for proliferation of PBMC collected from LTD cows, but PBMC collected at 21 d after calving had higher proliferative responses to LPS and ConA than those from late dry period or early lactation. In conclusion, results from this experiment confirmed the lower PBMC proliferation during the transition period from the final week of gestation to early lactation and suggested that cows transitioning from late lactation to dry period maintained unchanged cell-mediated immune function.

Histological tissue structure alterations resulting from Staphylococcus aureus intramammary infection in heifer mammary glands hormonally induced to rapidly grow and develop

Intramammary infections (IMI) are common in nonlactating dairy cattle and are expected to impair mammary growth and development and reduce future milk production. The objective of this study was to histologically evaluate how IMI alter tissue structure in growing and developing heifer mammary glands. A total of 18 nonpregnant, nonlactating heifers between 11 and 14 mo of age were used in the present study. Heifers received daily supraphysiological injections of estradiol and progesterone for 14 d to stimulate rapid mammary growth and development. One-quarter of each heifer was subsequently infused with Staphylococcus aureus (CHALL) while a second quarter served as an uninfected control (UNINF). Heifers were randomly selected and euthanized either the last day of hormonal injections to observe IMI effects on mammary gland growth (GRO), or 13 d post-injections, to observe IMI effects on mammary development (DEV). Mammary tissues were collected from the center and edge parenchymal regions of each mammary gland for morphometric tissue area evaluation. For GRO tissues, CHALL quarters had less epithelial tissue area and marginally more intralobular stroma tissue area than UNINF quarters. Tissue areas occupied by luminal space, extralobular stroma, adipose, and lobular tissue were similar. For DEV tissues, area occupied by epithelium, luminal space, intralobular stroma, and extralobular stroma did not differ between quarter treatments, but UNINF quarters had more adipose tissue area and marginally less lobular area than CHALL quarters. Results indicate that IMI in growing and developing mammary glands reduces mammary epithelial growth and alters mammary gland development by impairing epithelial branching into the mammary fat pad. Taken together, these tissue changes before calving may have adverse effects on milk production. Therefore, an important focus should be placed on improving udder health in replacement heifers through management strategies that mitigate the deleterious effects of IMI and promote the positive development of the mammary gland.

Endocrine changes during the peripartal period related to colostrogenesis in mammalian species

This review discusses endocrine and functional changes during the transition from late gestation to lactation that are related to the production of colostrum in different mammalian species. Species covered in this article include ungulate species (cattle, sheep, goats, pigs, horses), rodents (rat, mouse), rabbits, and carnivores (cats, dogs), as well as humans. An immediate availability of high quality colostrum for the newborn after birth is crucial in species where a transfer of immunoglobulins (Ig) does not or only partially occur via the placenta during pregnancy. Declining activity of gestagens, in most species progesterone (P4), is crucial at the end of pregnancy to allow for the characteristic endocrine changes to initiate parturition and lactation, but the endocrine regulation of colostrogenesis is negligible. Both, the functional pathways and the timing of gestagen withdrawal differ considerably among mammalian species. In species with a sustaining corpus luteum throughout the entire pregnancy (cattle, goat, pig, cat, dog, rabbit, mouse, and rat), a prostaglandin F2α (PGF2α)-induced luteolysis shortly before parturition is assumed to be the key event to initiate parturition as well as lactogenesis. In species where the gestagen production is taken over by the placenta during the course of gestation (e.g., sheep, horse, and human), the reduction of gestagen activity is more complex, as PGF2α does not affect placental gestagen production. In sheep the steroid hormone synthesis is directed away from P4 towards estradiol-17β (E2) to achieve a low gestagen activity at high E2 concentrations. In humans the uterus becomes insensitive to P4, as parturition occurs despite still high P4 concentrations. However, lactogenesis is not completed as long as P4 concentration is high. Early colostrum and thus Ig intake for immune protection is not needed for the human newborn which allows a delayed onset of copious milk secretion for days until the placenta expulsion causes the P4 drop. Like humans, horses do not need low gestagen concentrations for successful parturition. However, newborn foals need immediate immune protection through Ig intake with colostrum. This requires the start of lactogenesis before parturition which is not fully clarified. The knowledge of the endocrine changes and related pathways to control the key events integrating the processes of colostrogenesis, parturition, and start of lactation are incomplete in many species.

Glucocorticoids in preterm human milk

Background

Glucocorticoids (GCs), cortisol and cortisone, are essential regulators of many physiological responses, including immunity, stress and mammary gland function. GCs are present in human milk (HM), but whether maternal and infant factors are associated with HM GC concentration following preterm birth is unclear.

Materials and methods

HM samples were collected on postnatal day 5 and 10 and at 4 months’ corrected age (4m CA) in a cohort of moderate- and late-preterm infants. GCs in HM were measured by liquid chromatography-tandem mass spectrometry. Relationships between GCs in HM and both maternal and infant characteristics were investigated using Spearman’s correlations and linear mixed models.

Results

170 mothers of 191 infants provided 354 HM samples. Cortisol concentrations in HM increased from postnatal day 5–4m CA (mean difference [MD] 0.6 ± 0.1 ng/ml, p < 0.001). Cortisone concentration did not change across lactation but was higher than cortisol throughout. Compared to no antenatal corticosteroid (ANS), a complete course of ANS was associated with lower GC concentrations in HM through to 4m CA (cortisol: MD –0.3 ± 0.1 ng/ml, p < 0.01; cortisone MD –1.8 ± 0.4 ng/ml, p < 0.001). At 4m CA, higher maternal perceived stress was negatively associated with GC concentrations in HM (cortisol adjusted beta-coefficient [aβ] –0.01 ± 0.01 ng/ml, p = 0.05; and cortisone aβ –0.1 ± 0.03 ng/ml, p = 0.01), whereas higher postpartum depression and maternal obesity were associated with lower cortisone concentrations (aβ –0.1 ± 0.04 ng/ml p < 0.05; MD [healthy versus obese] –0.1 ± 0.04 ng/ml p < 0.05, respectively). There was a weak positive correlation between GC concentrations in HM and gestational age at birth (r = 0.1, p < 0.05). Infant birth head circumference z-score was negatively associated with cortisol concentrations (aβ –0.01 ± 0.04 ng/ml, p < 0.05). At hospital discharge, fat-free mass showed a weak positive correlation with cortisol concentrations (r = 0.2, p = 0.03), while fat mass showed a weak negative correlation with cortisone concentrations (r = –0.25, p < 0.001).

Conclusion

The mammary gland appears to protect the infant from cortisol through inactivation into cortisone. Maternal and infant characteristics were associated with concentration of GCs in HM, including ANS, stress and depression scores, obesity, gestational age and infant size. The effects of HM glucocorticoids on long-term health outcomes requires further research.

The role of the IGF system in mammary physiology of ruminants

The IGF system plays a central role in all stages of mammary development, lactation and involution. IGFs exert their effects on the mammary gland through both endocrine and paracrine/autocrine mechanisms and the importance of circulating versus local IGF action remains an open question, especially in ruminants. At the whole organ level, a critical role for IGFs in ductal morphogenesis and lobuloalveolar development has been established, while at the cellular level the ability of IGFs to stimulate cell proliferation and control cell survival contributes to the number of milk-secreting cells in the gland. Much of this work has been conducted in rodents which provide an affordable research model and allow for genetic manipulation of specific components of the IGF system. Research into the role of the IGF system in dairy cows has generally supported information obtained with rodents though large gaps in our knowledge remain and species differences are not well defined. Examples include whether exogenous somatotropin exerts its effects on the mammary gland through local IGF-1 synthesis which is accepted dogma in rodents, what the role of IGF-1 versus IGF-2 is in the mammary gland, and how the IGFBPs regulate IGF bioactivity. This last area is particularly under-investigated in ruminants both at the whole animal and the cellular and molecular levels. Given that the IGF system may underlie many management practices that could contribute to enhancing productive efficiency of lactation, more research into the basic biology of this important system is warranted.

Lactational Amenorrhea: Neuroendocrine Pathways Controlling Fertility and Bone Turnover

Lactation is a physiological state of hyperprolactinemia and associated amenorrhea. Despite the fact that exact mechanisms standing behind the hypothalamus-pituitary-ovarian axis during lactation are still not clear, a general overview of events leading to amenorrhea may be suggested. Suckling remains the most important stimulus maintaining suppressive effect on ovaries after pregnancy. Breastfeeding is accompanied by high levels of prolactin, which remain higher than normal until the frequency and duration of daily suckling decreases and allows normal menstrual function resumption. Hyperprolactinemia induces the suppression of hypothalamic Kiss1 neurons that directly control the pulsatile release of GnRH. Disruption in the pulsatile manner of GnRH secretion results in a strongly decreased frequency of corresponding LH pulses. Inadequate LH secretion and lack of pre-ovulatory surge inhibit the progression of the follicular phase of a menstrual cycle and result in anovulation and amenorrhea. The main consequences of lactational amenorrhea are connected with fertility issues and increased bone turnover. Provided the fulfillment of all the established conditions of its use, the lactational amenorrhea method (LAM) efficiently protects against pregnancy. Because of its accessibility and lack of additional associated costs, LAM might be especially beneficial in low-income, developing countries, where modern contraception is hard to obtain. Breastfeeding alone is not equal to the LAM method, and therefore, it is not enough to successfully protect against conception. That is why LAM promotion should primarily focus on conditions under which its use is safe and effective. More studies on larger study groups should be conducted to determine and confirm the impact of behavioral factors, like suckling parameters, on the LAM efficacy. Lactational bone loss is a physiologic mechanism that enables providing a sufficient amount of calcium to the newborn. Despite the decline in bone mass during breastfeeding, it rebuilds after weaning and is not associated with a postmenopausal decrease in BMD and osteoporosis risk. Therefore, it should be a matter of concern only for lactating women with additional risk factors or with low BMD before pregnancy. The review summarizes the effect that breastfeeding exerts on the hypothalamus-pituitary axis as well as fertility and bone turnover aspects of lactational amenorrhea. We discuss the possibility of the use of lactation as contraception, along with this method's prevalence, efficacy, and influencing factors. We also review the literature on the topic of lactational bone loss: its mechanism, severity, and persistence throughout life.

Late gestation hyperthermia: epigenetic programming of daughter's mammary development and function

Exposure to stressors during early developmental windows, such as prenatally (i.e., in utero), can have life-long implications for an animal's health and productivity. The mammary gland starts developing in utero and, like other developing tissues and organs, may undergo fetal programming. Previous research has implicated factors, such as prenatal exposure to endocrine disruptors or alterations in maternal diet (e.g., maternal over or undernutrition), that can influence the developmental trajectory of the offspring mammary gland in postnatal life. However, the direct links between prenatal insults and future productive outcomes are less documented in livestock species. Research on in utero hyperthermia effects on early-life mammary development is scarce. This review will provide an overview of key developmental milestones taking place in the bovine mammary gland during the pre- and postnatal stages. We will showcase how intrauterine hyperthermia, experienced by the developing fetus during the last trimester of gestation, derails postnatal mammary gland development and impairs its synthetic capacity later in life. We will provide insights into the underlying histological, cellular, and molecular mechanisms taking place at key postnatal developmental life stages, including birth, weaning and the first lactation, that might explain permanent detriments in productivity long after the initial exposure to hyperthermia. Collectively, our studies indicate that prenatal hyperthermia jeopardizes the normal developmental trajectory of the mammary gland from fetal development to lactation. Further, in utero hyperthermia epigenetically programs the udder, and possibly other organs critical to lactation, yielding a less resilient and less productive cow for multiple lactations.

Colostrogenesis: Role and Mechanism of the Bovine Fc Receptor of the Neonate (FcRn)

Colostrogenesis is a separate and unique phase of mammary epithelial cell activity occurring in the weeks before parturition and rather abruptly ending after birth in the bovine. It has been the focus of research to define what controls this process and how it produces high concentrations of specific biologically active components important for the neonate. In this review we consider colostrum composition and focus upon components that appear in first milked colostrum in concentrations exceeding that in blood serum. The Fc Receptor of the Neonate (FcRn) is recognized as the major immunoglobulin G (IgG) and albumin binding protein that accounts for the proteins' long half-lives. We integrate the action of the pinocytotic (fluid phase) uptake of extracellular components and merge them with FcRn in sorting endosomes. We define and explore the means of binding, sorting, and the transcytotic delivery of IgG1 while recycling IgG2 and albumin. We consider the means of releasing the ligands from the receptor within the endosome and describe a new secretion mechanism of cargo release into colostrum without the appearance of FcRn itself in colostrum. We integrate the insulin-like growth factor family, some of which are highly concentrated bioactive components of colostrum, with the mechanisms related to FcRn endosome action. In addition to secretion, we highlight the recent findings of a role of the FcRn in phagocytosis and antigen presentation and relate its significant and abrupt change in cellular location after parturition to a role in the prevention and resistance to mastitis infections.

Progress on the Regulation of Ruminant Milk Fat by Noncoding RNAs and ceRNAs

Milk fat is not only a key factor affecting the quality of fresh milk but also a major target trait forbreeding. The regulation of milk fat involves multiple genes, network regulation and signal transduction. To explore recent discoveries of pathway regulation, we reviewed the published literature with a focus on functional noncoding RNAs and epigenetic regulation in ruminants. Results indicate that miRNAs play key roles in the regulation of milk fat synthesis and catabolism in ruminants. Although few data are available, merging evidence indicates that lncRNAs and circRNAs act on milk fat related genes through indirect action with microRNAs or RNAs in the ceRNA network to elicit positive effects on transcription. Although precise regulatory mechanisms remain unclear, most studies have focused on the regulation of the function of target genes through functional noncoding RNAs. Data to help identify factors that can regulate their own expression and function or to determine whether self-regulation involves positive and/or negative feedback are needed. Despite the growing body of research on the role of functional noncoding RNA in the control of ruminant milk fat, most data are still not translatable for field applications. Overall, the understanding of mechanisms whereby miRNA, lncRNA, circRNA, and ceRNA regulate ruminant milk fat remains an exciting area of research.

Sodium salicylate reduced mRNA abundance of hypoxia-associated genes in MAC-T cells

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Sodium salicylate decreased abundance of transcripts involved in mammary development.

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Knockdown of HIF-1α did not prevent hypoxia-induced glucose transporter 1 expression.

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Few interactions between hypoxia and sodium salicylate were observed.

Hypoxia is an oxygen deficiency commonly found in growing tissues and is speculated to occur in the rapidly developing mammary gland in peripartum dairy cattle. Low oxygen concentrations can activate hypoxia-inducible factor-1 (HIF-1), which increases transcription of genes involved in angiogenesis (VEGFA) and glucose transport (GLUT1), among other processes. The mRNA stability of these genes is positively regulated by heterogeneous nuclear ribonucleoprotein D (HNRNPD; also known as AUF1). In our previous research, postpartum administration of sodium salicylate (SS) increased whole-lactation milk yield in multiparous cows but tended to reduce milk yield in primiparous cows. Because rapid mammary tissue development likely occurs in cows approaching first lactation, we hypothesized that SS inhibited the activation of HIF-1α and decreased transcription of downstream targets. MAC-T cells were treated with SS (100 μM) or control medium before incubation under either hypoxic (1% O₂) or normoxic conditions for 12 h. Additionally, cells were transfected with either HIF1A small interfering RNA (siRNA) or a scrambled siRNA negative control 48 h before hypoxia treatments. HIF1A, GLUT1, VEGFA, and HNRNPD were quantified relative to the internal control gene NENF. Transcript abundance was assessed using a linear mixed model with the fixed effects of SS, hypoxia, siRNA, and all 2- and 3-way interaction terms and the random effect of plate nested within hypoxia. Treatment with SS interacted with hypoxia for GLUT1, as SS reduced GLUT1 when MAC-T cells were cultured in normoxic conditions; however, no effect of SS was found in hypoxia-treated cells. Regardless of oxygen status, SS reduced HNRNPD and tended to decrease VEGFA mRNA relative to untreated cells. Hypoxia increased GLUT1, yet no effect was observed on VEGFA or HNRNPD. Small interfering RNA knocked down HIF1A, but no effect was found on GLUT1, VEGFA, or HNRNPD. In conclusion, SS reduced transcript abundance of genes involved with mammary gland development but generally did not interact with oxygen status.

Impact of heat stress and a feed supplement on hormonal and inflammatory responses of dairy cows

The aim of this trial was to evaluate the effects of an immunomodulatory supplement (OmniGen AF, OG; Phibro Animal Health Corp.) and heat stress on hormonal, inflammatory, and immunological responses of lactating dairy cows. Sixty multiparous Holstein cows were randomly assigned to 4 treatments in a 2 × 2 factorial arrangement using 2 environments: cooled using fans and misters, or noncooled, and 2 top-dressed feed supplements (56 g/d): OG or a placebo (CTL). Temperature-humidity index averaged 78 during the 8-wk trial. Blood was drawn to analyze cortisol, prolactin, and circulating tumor necrosis factor (TNF)-α and IL-10. Peripheral blood mononuclear cells (PBMC) were isolated and stimulated with hydrocortisone, prolactin, or lipopolysaccharide (LPS), individually or in several combinations, to assess induced proliferation and cytokine production. At d 52, 6 cows per treatment were injected i.v. with an LPS bolus (ivLPS) to assess hormone and cytokine responses. For cooled cows, feeding OG increased plasma cortisol concentration relative to CTL. Noncooled cows fed CTL had lower circulating TNF-α concentrations than noncooled-OG and cooled-CTL cows, with cooled-OG intermediate. Hydrocortisone+LPS-stimulated PBMC from OG cows tended to proliferate more than CTL. Relative to cooled cows, PBMC from noncooled cows produced more TNF-α and IL-10 when stimulated with LPS. Following ivLPS, cooled-OG cows had a greater cortisol response than the other treatments. In conclusion, OG supplementation enhanced cortisol release under basal condition and induced inflammation with cooling compared with CTL. This suggests that heat stress inhibits OG-mediated cortisol release. Heat stress seemed to enhance the inflammatory responses of PBMC from lactating cows. However, OG supplementation promoted PBMC proliferation under stress, or in the presence of hydrocortisone.

Energy metabolism of pregnant zebu and crossbred zebu dairy cattle

The purpose of this study was to determine the energy partition of pregnant F1 Holstein x Gyr with average initial body weight (BW) of 515.6 kg and Gyr cows with average initial BW of 435.1 kg at 180, 210 and 240 days of gestation, obtained using respirometry. Twelve animals in two groups (six per genetic group) received a restricted diet equivalent to 1.3 times the net energy for maintenance (NEm). The proportion of gross energy intake (GEI) lost as feces did not differ between the evaluated breeds and corresponded to 28.65% on average. The daily methane production (L/d) was greater for (P<0.05) F1 HxG compared to Gyr animals. However, when expressed as L/kg dry matter (DM) or as percentage of GEI there were no differences between the groups (P>0.05). The daily loss of energy as urine (mean of 1.42 Mcal/d) did not differ (P>0.05) between groups and ranged from 3.87 to 5.35% of the GEI. The metabolizable energy intake (MEI) of F1 HxG animals was greater (P < 0.05) at all gestational stages compared to Gyr cows when expressed in Mcal/d. However, when expressed in kcal/kg of metabolic BW (BW0,75), the F1 HxG cows had MEI 11% greater (P<0.05) at 240 days of gestation and averaged 194.39 kcal/kg of BW0,75. Gyr cows showed no change in MEI over time (P>0.05), with a mean of 146.66 kcal/kg BW0. 75. The ME used by the conceptus was calculated by deducting the metabolizable energy for maintenance (MEm) from the MEI, which was obtained in a previous study using the same cows prior to becoming pregnant. The values of NEm obtained in the previous study with similar non-pregnant cows were 92.02 kcal/kg BW0.75 for F1 HxG, and 76.83 kcal/kg BW0.75 for Gyr (P = 0.06). The average ME for pregnancy (MEp) was 5.33 Mcal/d for F1 HxG and 4.46 Mcal/d for Gyr. The metabolizability ratio, averaging 0.60, was similar among the evaluated groups (P>0.05). The ME / Digestible Energy (DE) ratio differed between groups and periods evaluated (P<0.05) with a mean of 0.84. The heat increment (HI) accounted for 22.74% and 24.38% of the GEI for F1 HxG and Gyr cows, respectively. The proportion of GEI used in the basal metabolism by pregnant cows in this study represented 29.69%. However, there were no differences between the breeds and the evaluation periods and corresponded to 29.69%. The mean NE for pregnancy (NEp) was 2.76 Mcal/d and did not differ between groups and gestational stages (P>0.05).

Effects of evaporative cooling and dietary zinc source on heat shock responses and mammary gland development in lactating dairy cows during summer

The objective of this study was to examine the effects of evaporative cooling and dietary supplemental Zn source on heat shock responses and mammary gland development of lactating dairy cows during summer. Seventy-two multiparous lactating Holstein cows were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement. Cows were either cooled (CL) or not cooled (NC) and fed diets supplemented with 75 mg of Zn/kg of dry matter (DM) from Zn hydroxychloride (IOZ) or 35 mg of Zn/kg of DM from Zn hydroxychloride plus 40 mg of Zn/kg of DM from Zn-Met complex (ZMC). The 168-d trial included a 12-wk baseline phase when all cows were cooled and fed respective dietary treatments, and a subsequent 12-wk environmental challenge phase when NC cows were deprived of evaporative cooling. Plasma was collected from a subset of cows (n = 24) at 1, 3, 5, 12, 26, 41, 54, 68, 81 d of the environmental challenge to measure heat shock protein (HSP) 70 concentration. Mammary biopsies were collected from another subset of cows (n = 30) at enrollment (baseline samples) and at d 7 and 56 of the environmental challenge to analyze gene expression related to heat shock response, apoptosis and anti-oxidative enzymes, and to examine apoptosis and cell proliferation using immunohistochemistry. Supplemental Zn source did not affect milk yield but NC cows produced less milk than CL cows. Supplemental Zn source had no effect on mammary gene expression of HSP27, 70, and 90 or plasma concentrations of HSP70. The NC cows had greater mammary gene expression of HSP than CL cows. Circulating HSP70 of NC cows gradually increased and was higher at 81 d of environmental challenge compared with CL cows. Relative to IOZ, ZMC cows tended to have lower total mammary cell proliferation but greater mammary apoptosis. There was a tendency of greater TNFRSF1A mRNA expression for ZMC compared with IOZ cows, which may suggest upregulated extrinsic apoptosis. At d 7 of environmental challenge, NC cows had numerically higher mammary apoptosis than CL cows although not statistically significant. The NC cows tended to have greater mRNA expression of CAT and SOD3 regardless of time, and had greater mRNA expression of GPX1 at d 56 and FAS at d 7 of the environmental challenge than CL cows. Relative to CL cows, mammary cell proliferation rate was higher for NC cows at d 56 of the environmental challenge. In conclusion, dietary source of supplemental Zn has substantial effect on mammary cell turnover in lactating dairy cows, and prolonged exposure to heat stress increases mammary cell proliferation.

Effects of white, yellow, and blue colored LEDs on milk production, milk composition, and physiological responses in dairy cattle

Light emitting diode (LED) is more energy efficient than incandescent or fluorescent light. This study was to evaluate effects of different colored LEDs on milk production, milk composition, and physiology of Holstein cow. According to milk production and parity, cows (n = 186) were allotted to four treatments: control (natural daylight), white, yellow, and blue LED groups. Of these, 40 cows that had passed 57 day-in-milk were used. Yellow and blue LED groups demonstrated greater rates of decline in milk production than control and white LED groups. At the finish point, milk fat, protein, and lactose contents were the lowest in the blue LED group, whereas milk-urea-nitrogen levels were the highest in the yellow and blue LED groups. Extended exposure to blue LED light lowered antioxidant enzyme activity and insulin-like growth factor-1 levels. Prolactin concentrations were higher in the white and blue LED groups than in the control. Cortisol level was the highest in the blue LED group among the groups. Nonesterified fatty acid levels in the yellow and blue LED groups decreased to the greatest extent compared to the start point. These results suggest that blue LED light can decrease milk production and generate more stress than white and yellow LED lights.

Effect of heat stress during the early and late dry period on mammary gland development of Holstein dairy cattle

Dry period heat stress impairs subsequent milk yield. Our objective was to evaluate the effect of heat stress or cooling during the early and late dry period on mammary gland gene expression and microstructure. Cows were dried off ∼45 d before expected parturition and randomly assigned to 1 of 2 treatments: heat stress (HT, n = 39) or cooling (CL, n = 39) during the first 21 d of the dry period. On d 22, cows were switched or remained on HT and CL and this yielded 4 treatments: heat stress during the entire dry period (HTHT, n = 18); cooling during the entire dry period (CLCL, n = 20); HT for the first 21 d dry, then CL until calving (HTCL, n = 21); or CL for the first 21 d dry, then HT until calving (CLHT, n = 19). Data were analyzed in 2 periods: first 21 d dry (early dry period) and from 22 d until calving (late dry period) and analyzed using PROC MIXED or GLM in SAS (SAS Institute Inc., Cary, NC). Mammary biopsies (5-8 cows/treatment) were collected at -3, 3, 7, 14, and 25 d relative to dry-off to evaluate mammary gland gene expression and histology [i.e., cellular apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling) and proliferation (Ki67)]. Mammary alveoli number and connective tissue were visualized by hematoxylin and eosin and Mason's trichrome staining, respectively. During the early dry period, CL upregulated expression of CASP3, IGF1R, HSP90, HSF1, BECN1, ATG3, ATG5, and PRLR-LF relative to HT. However, in the late dry period, CLHT treatment upregulated expression of CASP3, CASP8, HSP70, HSP90, PRLR-LF, STAT5, CSN2, and ATG3 relative to CLCL. During the early dry period, cows exposed to HT had reduced mammary and stroma cell apoptosis and proliferation relative to CL. In addition to these findings, cows exposed to HT had lower connective tissue 3 d after dry-off relative to CL. However, in the late dry period, HTHT cows had higher connective tissue relative to CLCL. Also, in the early dry period, cows exposed to HT had greater alveoli number relative to CL, and HT decreased expression of genes related to autophagy and apoptosis in the early dry period, consistent with a delay in involution with HT. Thus, cows exposed to HT have extended involution with delayed apoptosis and autophagy signaling. Also, HT compromises mammary gland cell proliferation and leads to higher connective tissue later in the dry period. These results provide evidence that heat stress impairs overall mammary gland turnover during the dry period, which then affects secretory activity and productivity in the next lactation.

The inhibitory effect of melatonin on mammary function of lactating dairy goats†

The direct role of melatonin in mammary glands of dairy goats has remained obscure. This study aimed to evaluate the expression of melatonin membrane receptors (MT1 and MT2) in the pituitary and mammary glands of dairy goats during lactation, and to investigate the role of melatonin in mammary function. Both MT1 and MT2 were consistently expressed in the pituitary and mammary eight glands throughout the lactation period, and their levels were lower in 9 March (group I), June (group III), and September (group V) than in May (group II) and August (group IV). The expression patterns of pituitary and mammary MT1 and MT2 were consistent with those of blood melatonin during lactation. Furthermore, the mammary prolactin (PRL), and pituitary growth hormone (GH) and PRL mRNA expression showed an inverse trend in relation to blood melatonin levels. In mammary tissues, MT1 and MT2 immunoreactivity was predominantly located in the mammary epithelial cells (MECs). In addition, a dose- and time-dependent inhibition on cell viability was observed in cultured MECs. At the dose of 10 and 100 pg/ml, melatonin decreased mammary β-casein and PRL expression. Furthermore, the inhibitory effects of melatonin were blocked by luzindole, a nonselective MT1 and MT2 receptor antagonist. In addition, melatonin promoted MT1 and MT2 expression in cultured MECs. In conclusion, the presence of MT1 and MT2 in the pituitary and mammary glands and the inhibitory effects of melatonin on cell viability, β-casein, and PRL expression in MECs suggest the potential regulation by melatonin in goat mammary function.

Contrasting effects of transforming growth factor β1 on programmed cell death of bovine mammary epithelial cell lines MAC-T and BME-UV1

A previous study in the bovine mammary epithelial cell line BME-UV1 demonstrated that suppression of the phosphatidylinositol-4,5-biphosphate 3 kinase (PI3K)/AKT (somatotropic) signaling pathway was required for transforming growth factor β1 (TGFβ1)-induced programmed cell death (PCD). To investigate whether this is a universal mechanism for TGFβ1 to induce PCD in bovine mammary epithelium, we compared TGFβ1 modulation of PI3K/AKT and its role in PCD in 2 bovine mammary epithelial cell lines: MAC-T and BME-UV1. In MAC-T cells, TGFβ1 promoted cell survival, and this paralleled a reduction in PI3K/AKT activity, rather than an increase. In BME-UV1 cells, TGFβ1 induced PCD, and this was accompanied by a time-dependent effect on PI3K/AKT activity, including an initial significant increase in the phosphorylation of AKT at 3 h, followed by a reduction between 12 and 24 h, and then an increase at 48 h. Inhibition of AKT activity enhanced TGFβ1-induced PCD in BME-UV1 cells but had no effect on MAC-T cells, suggesting that TGFβ1 mediates PCD in BME-UV1 cells through suppression of AKT activity. Inhibition of TGFβ receptor type I (TβRI) kinase activity completely abrogated TGFβ1-induced PCD in BME-UV1 cells but had no effect on TGFβ1-induced suppression of PCD in MAC-T cells, demonstrating that TGFβ1-induced PCD in BME-UV1 cells is dependent on TβRI/SMAD signaling. These and previous observations suggest that the different effects of TGFβ1 on PCD in these cell lines might involve noncanonical signaling pathways other than PI3K/AKT, and may reflect their different lineages. Future studies should address this finding, taking into consideration the effect that different culture conditions might have on cell phenotype.

Late gestation heat stress in dairy cows: Effects on dam and daughter

In dairy cattle, the final weeks before parturition are physiologically challenging and an important determinant of subsequent production performance. External stressors should be carefully managed during this period to avoid adding strain on the animals. Late-gestation heat stress impairs productivity in the dam and exerts transgenerational effects on progeny. Physiological responses are complex and detriments to performance are multifaceted. Late-gestation heat stress blunts mammary gland involution in the first half of the dry period and impairs cell proliferation as calving approaches. Moreover, cows that were exposed to prepartum heat-stress exhibit reduced adipose tissue mobilization and a lower degree of insulin resistance during early lactation. Prepartum heat exposure also depresses immune function and evidence links this decrease to altered prolactin signaling under heat stress. Placental functions are also impaired as reflected in a higher cotyledon mass but lower maternal circulating estrone sulfate concentrations, potentially resulting in lower nutrient supply and reduced calf birth weight. In addition, calves born to heat-stressed dams show impaired immune function and therefore higher disease susceptibly. Novel evidence reported that intrauterine heat stress alters the methylation profile of liver and mammary DNA, which may also contribute to the poorer performance during adulthood of calves exposed to heat stress in utero. Understanding the contribution of all altered biological systems during late-gestation heat stress can be used as a basis for improving cow management during the dry period. This article provides a review of the impacts of late-gestation heat stress and of the emerging understanding of the biological mechanisms that underlie the observed impairments of performance.

Leucine promotes the growth of squabs by increasing crop milk protein synthesis through the TOR signaling pathway in the domestic pigeon (Columba livia)

Leucine (Leu) plays a critical regulatory role in protein synthesis, however, the effects and molecular mechanisms of Leu on crop milk protein in the domestic pigeons (Columba livia) are still unknown. Therefore, the study aimed to investigate the effects of dietary Leu supplementation on crop milk protein synthesis and the growth performance of squabs and the possible underlying mechanism. A total of 240 pairs of breeding pigeons (1102.3 ± 9.5 g/pair) were randomly assigned to 1 of 5 treatments, including a positive control (PC) diet that had adequate crude protein (crude protein, CP = 18%; Leu = 1.30%), a negative control (NC) diet that was low in CP (CP = 16%, Leu = 1.30%), and NC diets supplemented with Leu at 0.15%, 0.45%, or 1.05%. Compared with the NC diet, 0.15 to 0.45% Leu supplementation decreased BW loss and increased relative crop weight, crop thickness, and protein levels in the crop tissue and milk of breeding pigeons. However, dietary supplementation with 1.05% Leu inhibited ADFI in breeding pigeons. Dietary supplementation with 0.15 to 0.45% Leu decreased the mortality rate and increased the BW, eviscerated yield, and breast muscle yield of young squabs. The protein expression levels of the target of rapamycin (TOR), ribosomal protein S6 kinase 1 (S6K1), ribosomal protein S6 kinase (S6), eukaryotic initiation factor 4E binding protein 1 (4EBP1), and eukaryotic translation initiation factor 4E (eIF4E) were upregulated in the crop tissue of breeding pigeons in PC, 0.15% and 0.45% Leu-supplemented groups. Collectively, these results indicated that 0.15 to 0.45% Leu supplementation could decrease BW loss, increase milk protein synthesis in the crop of breeding pigeons, and enhance the survival rate and growth performance of young squabs through the TOR signaling pathway.

Fecal stress, nutrition and reproductive hormones for monitoring environmental impacts on tigers (Panthera tigris)

Non-invasive stress and nutritional hormone analysis in relation to ecological and other biological indices have tremendous potential to address environmental disturbance impacts on wildlife health. To this end, we examined the relation between glucocorticoid (GC) and thyroid (T3) hormone indices of disturbance and nutritional stress in response to ACTH and TSH challenges in captive tigers, as well as how reproductive hormones vary by sex and reproductive condition. Glucocorticoid, thyroid, progesterone and androgen assays conducted on high-performance liquid chromatography separated fractions of biologically relevant fecal extracts revealed high cross-reactivity of these assays for their respective biologically relevant fecal hormone metabolites. Both adrenal and thyroid hormone metabolites were elevated in response to ACTH and TSH challenges. However, the adrenal and thyroid hormone responses to ACTH challenge were concurrent, whereas the adrenal response to TSH challenge was delayed relative to thyroid hormone elevation in both males and females. The concurrently elevated T3 in response to ACTH may serve to raise metabolic rate to maximize use of GC-mobilized glucose, whereas the relatively delayed GC rise following TSH challenge may be a response to glucose depletion due to increased metabolic rate associated with elevated T3. Progesterone, testosterone and androstenedione hormone metabolites were significantly elevated during gestation compared to lactation in a female monitored from conception through early lactation. Results suggest that the glucocorticoid, thyroid and reproductive hormone assays we tested can accurately measure the stress, nutrition and reproductive response from tiger feces, providing useful non-invasive tools to assess physiological responses to environmental stressors and their reproductive consequences in the wild.

Hyperprolactinaemia

Hyperprolactinaemia is one of the most common problems in clinical endocrinology. It relates with various aetiologies (physiological, pharmacological, pathological), the clarification of which requires careful history taking and clinical assessment. Analytical issues (presence of macroprolactin or of the hook effect) need to be taken into account when interpreting the prolactin values. Medications and sellar/parasellar masses (prolactin secreting or acting through “stalk effect”) are the most common causes of pathological hyperprolactinaemia. Hypogonadism and galactorrhoea are well-recognized manifestations of prolactin excess, although its implications on bone health, metabolism and immune system are also expanding. Treatment mainly aims at restoration and maintenance of normal gonadal function/fertility, and prevention of osteoporosis; further specific management strategies depend on the underlying cause. In this review, we provide an update on the diagnostic and management approaches for the patient with hyperprolactinaemia and on the current data looking at the impact of high prolactin on metabolism, cardiovascular and immune systems.

Long-term effects of prior diets, dietary transition and pregnancy on adipose gene expression in dairy heifers

Adipose tissue is highly involved in whole-body metabolism and is the main site for lipid synthesis, storage and mobilization in ruminants. Therefore, knowledge about adipose tissue responses to different diets is important, especially in growing heifers as the feeding regimes of replacement heifers affect their future success as dairy cows. However, at gene expression level such knowledge is limited. As part of a larger feed trial, adipose tissue biopsies from 24 Norwegian Red heifers were collected at 12 months of age (12MO) and at month seven of gestation (PREG) and analyzed by next-generation mRNA sequencing. Between these two sampling points, all heifers had gone through a successful conception and a feed change from four dietary treatments of high or low energy (HE/LE) and protein (HP/LP) content (treatments LPHE, HPHE, LPLE and HPLE) to a low-energy, low-protein pregnancy feed given to all animals. Gene expression differences between different feed treatments at 12MO are described in an earlier publication from our group. The main objectives of this study were to investigate the long-term effects of diets differing in protein and energy density level on gene expression in adipose tissue of growing replacement dairy heifers. To achieve this, we examined the post-treatment effects between the treatment groups at month seven of gestation; 6 months after the termination of experimental feeding, and the long-term gene expression changes occurring in the adipose tissue between 12MO and PREG. Post-treatment group comparisons showed evidence of long-term effects of dietary treatment on adipose gene expression. Differences between protein treatments were smaller than between energy treatments. Adipose gene expression changes from 12MO to PREG were much larger for the HE than the LE treatments and seemed to mostly be explained by the characteristics of the diet change. 97 genes displayed a unidirectional expression change for all groups from 12MO to PREG, and are considered to be treatment-independent, possibly caused by pregnancy or increased age. This study provides candidate genes and key regulators for further studies on pregnancy preservation (TGFB1, CFD) and metabolic regulation and efficiency (PI3K, RICTOR, MAP4K4,) in dairy cattle.

PHYSIOLOGY SYMPOSIUM: Effects of heat stress during late gestation on the dam and its calf12

Heat stress during late gestation in cattle negatively affects the performance of the dam and its calf. This brief exposure to an adverse environment before parturition affects the physiological responses, tissue development, metabolism, and immune function of the dam and her offspring, thereby limiting their productivity. During the dry period of a dairy cow, heat stress blunts mammary involution by attenuating mammary apoptosis and autophagic activity and reduces subsequent mammary cell proliferation, leading to impaired milk production in the next lactation. Dairy cows in early lactation that experience prepartum heat stress display reduced adipose tissue mobilization and lower degree of insulin resistance in peripheral tissues. Similar to mammary gland development, placental function is impaired by heat stress as evidenced by reduced secretion of placental hormones (e.g., estrone sulfate) in late gestation cows, which partly explains the reduced fetal growth rate and lighter birth weight of the calves. Compared with dairy calves born to dams that are exposed to evaporative cooling during summer, calves born to noncooled dry cows maintain lower BW until 1 yr of age, but display a stronger ability to absorb glucose during metabolic challenges postnatally. Immunity of the calves, both passive and cell-mediated immune function, is also impaired by prenatal heat stress, resulting in increased susceptibility of the calves to diseases in their postnatal life. In fact, dairy heifers born to heat-stressed dry cows without evaporative cooling have a greater chance leaving the herd before puberty compared with heifers born to dry cows provided with evaporative cooling (12.2% vs. 22.7%). Dairy heifers born to late-gestation heat-stressed dry cows have lower milk yield at maturity during their first and second lactations. Emerging evidence suggests that late-gestation heat stress alters the mammary gland microstructure of the heifers during the first lactation and exerts epigenetic alterations that might explain, in part, their impaired productivity.

TGF-beta signalling in bovine mammary gland involution and a comparative assessment of MAC-T and BME-UV1 cells as in vitro models for its study

The goal of the dairy industry is ultimately to increase lactation persistency, which is the length of time during which peak milk yield is sustained. Lactation persistency is determined by the balance of cell apoptosis and cell proliferation; when the balance is skewed toward the latter, this results in greater persistency. Thus, we can potentially increase milk production in dairy cows through manipulating apoptogenic and antiproliferative cellular signaling that occurs in the bovine mammary gland. Transforming growth factor beta 1 (TGFβ1) is an antiproliferative and apoptogenic cytokine that is upregulated during bovine mammary gland involution. Here, we discuss possible applications of TGFβ1 signaling for the purposes of increasing lactation persistency. We also compare the features of mammary alveolar cells expressing SV-40 large T antigen (MAC-T) and bovine mammary epithelial cells-clone UV1 (BME-UV1) cells, two extensively used bovine mammary epithelial cell lines, to assess their appropriateness for the study of TGFβ1 signaling. TGFβ1 induces apoptosis and arrests cell growth in BME-UV1 cells, and this was reported to involve suppression of the somatotropic axis. Conversely, there is no proof that exogenous TGFβ1 induces apoptosis of MAC-T cells. In addition to TGFβ1's different effects on apoptosis in these cell lines, hormones and growth factors have distinct effects on TGFβ1 secretion and synthesis in MAC-T and BME-UV1 cells as well. MAC-T and BME-UV1 cells may behave differently in response to TGFβ1 due to their contrasting phenotypes; MAC-T cells have a profile indicative of both myoepithelial and luminal populations, while the BME-UV1 cells exclusively contain a luminal-like profile. Depending on the nature of the research question, the use of these cell lines as models to study TGFβ1 signaling should be carefully tailored to the questions asked.

Effects of Staphylococcus aureus intramammary infection on the expression of estrogen receptor α and progesterone receptor in mammary glands of nonlactating cows administered estradiol and progesterone to stimulate mammary growth

Intramammary infections (IMI) are prevalent in nonlactating dairy cattle and are known to alter mammary structure and negatively affect the amount of mammary epithelium in the gland. Mechanisms responsible for the observed changes in mammary growth during an IMI are poorly understood, yet the importance of the key mammogenic hormones driving mammary growth is well recognized. This study's objective was to characterize the expression of estrogen receptor α (ESR1) and progesterone receptor (PGR) in mammary glands stimulated to grow and develop in the presence or absence of an IMI as well as preliminarily characterize myoepithelial cell response to IMI. Mammary growth was stimulated in 18 nonpregnant, nonlactating dairy cows using subcutaneous estradiol and progesterone injections, and 2 culture-negative quarters of each cow were subsequently infused with either saline (n = 18) or Staphylococcus aureus (n = 18). Mammary parenchyma tissues were collected 5 d (n = 9) or 10 d (n = 9) postchallenge and examined using immunofluorescence microscopy to quantify positive nuclei and characterize staining features. There tended to be a greater number of ESR1-positive nuclei observed across 8 random mammary parenchyma fields of view in saline quarters than in Staph. aureus quarters (201 vs. 163 ± 44 nuclei). Saline quarters also contained a greater number of PGR-positive nuclei (520 vs. 440 ± 45 nuclei) and myoepithelial cells (971 vs. 863 ± 48 nuclei) than Staph. aureus-challenged quarters. However, when ESR1, PGR, and myoepithelial nuclei counts were adjusted for Staph. aureus quarters containing less epithelium, differences between quarter treatments abated. The examined ESR1 and PGR staining characteristics were similar between saline and Staph. aureus quarters but were differentially affected by day of tissue collection. Additionally, nuclear staining area of myoepithelial cells was greater in Staph. aureus quarters than in saline quarters. These results indicate that IMI had little effect on the number or staining characteristics of ESR1- or PGR-positive nuclei relative to epithelial area, but myoepithelial cells appear to be affected by IMI and the associated inflammation in nonlactating mammary glands that were stimulated to grow rapidly using mammogenic hormones. Accordingly, reductions in mammary epithelium in affected glands are not suspected to be resultant of alterations in the number or staining characteristics of ESR1- or PGR-positive mammary epithelial cells.

Effect of repeated trace mineral injections on beef heifer development and reproductive performance

To determine the effects of repeated trace mineral injections on heifer development and reproductive performance, commercial Angus heifers (n = 290; 199 ± 34.3 kg; 221 ± 22 d of age) were utilized in a completely randomized design. Heifers were stratified by body weight (BW) and were administered an injectable trace mineral (MM; Multimin 90) or saline (CON) given subcutaneously, post-weaning at 221, 319, 401, and 521 ± 22 d of age. Throughout development, heifers grazed endophyte-infected fescue, red clover pastures and were supplemented with corn distillers grains (2.7 kg per heifer per day) and given access to free choice inorganic minerals. Heifer BW and body condition scores (BCS) were collected at trial initiation and 4- to 7-wk intervals thereafter. Hair coat scores (HCS) and respiration rates (n = 30 heifers per treatment) were collected at 269, 310, and 361 ± 22 d of age. Blood and liver samples were collected at trial initiation and estrous synchronization from 30 heifers per treatment to determine trace mineral status. At 319, 372, and 421 ± 22 d of age, antral follicle count and ovarian size were determined via ultrasonography. Two blood samples from all heifers were collected 10 d apart, concurrent with ultrasound dates, for cyclicity determination. Estrous synchronization was initiated, and reproductive tract scores (RTS) were collected at 421 ± 22 d of age, and heifers were bred via artificial insemination (AI) at 430 ± 22 d of age. Heifer BW, BCS, and HCS did not differ (P ≥ 0.12) throughout development, except at 268 ± 22 d of age when BCS was greater (P = 0.03) for MM than CON heifers. Respiratory rates were greater (P = 0.05) for MM than CON heifers at 269 ± 22 d of age but did not differ (P ≥ 0.66) at 310 and 361 ± 22 d of age. Plasma Mn and Zn concentrations did not differ (P ≥ 0.54). However, MM heifers had greater (P ≤ 0.01) plasma and liver concentrations of Cu and Se compared to CON. Interestingly, MM decreased (P = 0.02) liver Zn concentrations compared to CON, and there was no difference (P = 0.60) in liver Mn. Antral follicle count and ovarian size did not differ (P ≥ 0.51) due to treatment. Throughout development, number of heifers cycling was lesser (P < 0.01) for MM than CON heifers. However, there was no difference (P ≥ 0.19) in RTS, AI pregnancy rates, or overall pregnancy rates. Supplementing an injectable trace mineral increased heifer Cu and Se status; however, no effect was noted on ovarian development or pregnancy rates.

Responses to pup vocalizations in subordinate naked mole-rats are induced by estradiol ingested through coprophagy of queen's feces

Naked mole-rats form eusocial colonies consisting of a single breeding female (the queen), several breeding males, and sexually immature adults (subordinates). Subordinates are cooperative and provide alloparental care by huddling and retrieving pups to the nest. However, the physiological mechanism(s) underlying alloparental behavior of nonbreeders remains undetermined. Here, we examined the response of subordinates to pup voice and the fecal estradiol concentrations of subordinates during the three reproductive periods of the queen, including gestation, postpartum, and nonlactating. Subordinate response to pup voice was observed only during the queen's postpartum and was preceded by an incremental rise in subordinates' fecal estradiol concentrations during the queen's gestation period, which coincided with physiological changes in the queen. We hypothesized that the increased estradiol in the queen's feces was disseminated to subordinates through coprophagy, which stimulated subordinates' responses to pup vocalizations. To test this hypothesis, we fed subordinates either fecal pellets from pregnant queens or pellets from nonpregnant queens amended with estradiol for 9 days and examined their response to recorded pup voice. In both treatments, the subordinates exhibited a constant level of response to pup voice during the feeding period but became more responsive 4 days after the feeding period. Thus, we believe that we have identified a previously unknown system of communication in naked mole-rats, in which a hormone released by one individual controls the behavior of another individual and influences the level of responsiveness among subordinate adults to pup vocal signals, thereby contributing to the alloparental pup care by subordinates.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Plasticity of mammary development in the prepubertal bovine mammary gland

Although peripubertal mammary development represents only a small fraction of the total mass of mammary parenchyma present in the udder at the end of gestation and into lactation, there is increasing evidence that the tissue foundations created in early life can affect future mammary development and function. Studies on expression of estrogen and progesterone receptors seem to confirm the relevance of these steroids in prepubertal mammary development, but connections with other growth factors, hormones, and local tissue factors remain elusive. Enhanced preweaning feeding in the bovine appears to enhance the capacity of mammary tissue to response to mammogenic stimulation. This suggests the possibility that improved early nutrition might allow for creation of stem or progenitor cell populations to better support the massive ductal growth and lobulo-alveolar development during gestation. Increasing evidence that immune cells are involved in mammary development suggests there are unexpected and poorly understood connections between the immune system and mammary development. This is nearly unexplored in ruminants. Development of new tools to identify, isolate, and characterize cell populations within the developing bovine mammary gland offer the possibility of identifying and perhaps altering populations of mammary stem cells or selected progenitor cells to modulate mammary development and, possibly, mammary function.

Ghrelin is expressed in the pregnant mammary glands of dairy goats and promotes the cell proliferation of mammary epithelial cells

Little is known about ghrelin's effects on cell proliferation in pregnant mammary epithelial cells (MECs) even though it is known to be a mitogen for a variety of other cell types. The objectives of this study were to evaluate the expression and localization of ghrelin and its functional receptor, GHSR-1a, in the mammary glands of dairy goats during pregnancy and to investigate the direct role of ghrelin in cell proliferation of primary cultured MECs. Compared to the early stage (days 30) of pregnancy, the abundance of transcripts and protein of ghrelin and GHSR-1a were significantly greater in mid- and late-phases (between days 90 and days 120) of pregnancy (p < .05). Immunohistochemistry analysis showed that ghrelin and GHSR-1a were predominantly localized in the alveolar and ductal mammary epithelial cells at various stages of pregnancy. In our in vitro experiments, ghrelin induced a dose- and time-dependent promotory effect on cell proliferation of MECs. At the dose of 10³ pg/mL treatment 24 h, ghrelin augmented the expression of proliferation-related peptides (PCNA and cyclin B1). Furthermore, ghrelin promoted the expression of prolactin (PRL) and GHSR-1a in cultured MECs. Additionally, the stimulatory effects of ghrelin were blocked by d-Lys3-GHRP6, a selective antagonist of GHSR-1a. As the temporal changes in ghrelin and GHSR-1a expression in pregnant goat mammary glands coincided with the mammary growth and development during the pregnancy, activation of GHSR-1a signal transduction pathways by ghrelin may play a direct role in the regulation of mammary growth in dairy goats.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA:Historical perspectives of lactation biology in the late 20th and early 21st centuries

The latter half of the 20th century and the early portion of the 21st century will be recognized as the "Golden Age" of lactation biology. This period corresponded with the rise of systemic, metabolomic, molecular, and genomic biology. It includes the discovery of the structure of DNA and ends with the sequencing of the complete genomes of humans and all major domestic animal species including the dairy cow. This included the ability to identify polymorphisms in the nucleic acid sequence, which can be tied to specific differences in cellular, tissue, and animal performance. Before this period, classical work using endocrine ablation and replacement studies identified the mammary gland as an endocrine-dependent organ. In the early 1960s, the development of RIA and radioreceptor assays permitted the study of the relationship between endocrine patterns and mammary function. The ability to measure nucleic acid content of tissues opened the door to study of the factors regulating mammary growth. The development of high-speed centrifugation in the 1960s allowed separation of specific cell organelles and their membranes. The development of transmission and scanning electron microscopy permitted the study of the relationship between structure and function in the mammary secretory cell. The availability of radiolabeled metabolites provided the opportunity to investigate the metabolic pathways and their regulation. The development of concepts regarding the coordination of metabolism to support lactation integrated our understanding of nutrient partitioning and homeostasis. The ability to produce recombinant molecules and organisms permitted enhancement of lactation in farm animal species and the production of milk containing proteins of value to human medicine. These discoveries and others contributed to vastly increased dairy farm productivity in the United States and worldwide. This review will include the discussion of the centers of excellence and scientists who labored in these fields to produce the harvest of knowledge we enjoy today.

A genomic study on mammary gland acclimatization to tropical environment in the Holstein cattle

This study aims at identifying mammary gland genes expressed in Brazilian Holstein cattle produced under tropical conditions, as compared to the Portuguese Holstein cattle produced in a temperate region. For this purpose, cDNA microarrays and real-time (RT) PCR transcriptomic techniques were utilized in 12 Holstein cows from the same lactating phase and management systems divided into two groups: Holstein Brazil (HB) originated from Brazil and Holstein Portugal (HP) from Portugal. The genomic results show that from a total of 4608 genes available from the microarray slide (Bovine Long Oligo (BLO) library), 65 transcripts were identified as differentially expressed in mammary glands. The genes associated with mammary gland development and heat stress responses showed greater expression in HB animals. In the HP group, upregulated genes related with apoptosis and vascular development and downregulated genes related with resistance to heat stress were observed. Validation of microarray results was done using RT-PCR. HB animals had higher blood levels of growth hormone than HP animals. Blood levels of prolactin and T₃ were similar for both groups and GH levels were increased in the HB group. The results suggest a gene change towards long-term acclimatization of Brazilian Holstein cattle to cope with tropical heat stress conditions.

Establishment of a 3D cell culture model of primary bovine mammary epithelial cells extracted from fresh milk

For the investigation of molecular processes underlying diseases of the bovine mammary gland, primary bovine mammary epithelial cells (pbMEC) are used. They are known to contribute to the innate immune system of the bovine mammary gland. The functionality of pbMEC depends on the maintenance of in vivo characteristics. So far, the optimization of pbMEC culture conditions was intended in a variety of experiments. For this purpose, most of the studies used stable cell lines or primary cells obtained from udder biopsies of slaughtered animals. By contrast, within our study, pbMEC of healthy and first lactating Brown Swiss cows were non-invasively isolated from fresh milk. The non-invasively isolated pbMEC were cultivated on the extracellular matrix-like scaffold Matrigel®_. Further, they were challenged with different compositions of proliferation media, containing lactogenic hormones and/or the essential amino acid L-lysine. Changes in expression levels of genes coding for milk proteins and for components of the janus kinase/signal transducers and activators of transcription (JAK-STAT) and mTOR pathways were analyzed by RT-qPCR. The secreted proteins were analyzed by LC-MS/MS measurements. We showed for the first time the establishment of a physiologically functional 3D cell culture model of pbMEC isolated from fresh milk. This represents a primary cell culture model system, based on non-invasive cell collection, that can be used to unravel physiological processes in an unbiased manner.

MicroRNA roles in signalling during lactation: an insight from differential expression, time course and pathway analyses of deep sequence data

The study examined microRNA (miRNA) expression and regulatory patterns during an entire bovine lactation cycle. Total RNA from milk fat samples collected at the lactogenesis (LAC, day1 [D1] and D7), galactopoiesis (GAL, D30, D70, D130, D170 and D230) and involution (INV, D290 and when milk production dropped to 5 kg/day) stages from 9 cows was used for miRNA sequencing. A total of 475 known and 238 novel miRNAs were identified. Fifteen abundantly expressed miRNAs across lactation stages play regulatory roles in basic metabolic, cellular and immunological functions. About 344, 366 and 209 miRNAs were significantly differentially expressed (DE) between GAL and LAC, INV and GAL, and INV and LAC stages, respectively. MiR-29b/miR-363 and miR-874/miR-6254 are important mediators for transition signals from LAC to GAL and from GAL to INV, respectively. Moreover, 58 miRNAs were dynamically DE in all lactation stages and 19 miRNAs were significantly time-dependently DE throughout lactation. Relevant signalling pathways for transition between lactation stages are involved in apoptosis (PTEN and SAPK/JNK), intracellular signalling (protein kinase A, TGF-β and ERK5), cell cycle regulation (STAT3), cytokines, hormones and growth factors (prolactin, growth hormone and glucocorticoid receptor). Overall, our data suggest diverse, temporal and physiological signal-dependent regulatory and mediator functions for miRNAs during lactation.

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

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

Variation of Human Milk Glucocorticoids over 24 hour Period

Human milk (HM) contains a complex array of hormones, including members of the glucocorticoid family. The predominant glucocorticoids, cortisol and cortisone may influence the growth and behaviour of the breastfed infant. However, little is understood of the factors regulating the levels of these hormones within HM. The aim of the study was to examine HM cortisol and cortisone concentration, measured in samples collected at each feed during a 24 hour period. Twenty three exclusively breastfeeding mothers collected milk, prior to and after each breastfeeding session over 24 hour period at 3.2(1.60) months. HM cortisol and cortisone levels were measured using high pressure liquid chromatography mass spectroscopy. Cortisone was the predominant glucocorticoid (3.40 ng/ml), and cortisol was detected in all samples (1.62 ng/ml). A positive correlation was found between cortisone and cortisol (r = 0.61, y = 1.93 ± 0.24, p < 0.0001). Cortisol and cortisone concentrations were significantly higher in feeds in the morning (2.97 ng/ml and 4.88 ng/ml), compared to afternoon (1.20 ng/ml and 3.54 ng/ml), evening (0.69 ng/ml and 2.13 ng/ml) and night (1.59 and 3.27 ng/ml). No difference was found between glucocorticoids level of the milk expressed for collection either before or immediately after the breastfeed, or between milk collected from the left or right breast. This study shows that HM glucocorticoid concentrations exhibit a 24 hour pattern, with highest peak levels in the early morning, reflecting the circadian pattern as previously reported in plasma. Thus, HM glucocorticoid concentrations are likely to reflect those in the maternal circulation.