Review: Mammary development in swine: effects of hormonal status, nutrition and management

Effect of two milk supplements and two ways of administration on growth performance, welfare and fecal microbial ecology of suckling piglets

Introduction

The aim of this study was to evaluate the effect of two MS formulas, DanMilk™ (AB Neo, Denmark) (MS1) and Neopigg® RescueMilk (Provimi, Netherlands) (MS2) administered manually and to compare two ways of administration (manual vs automatic) of MS1 on growth performance, health, fecal microbial profile, behavior, and skin lesions of piglets during suckling and post-weaning.

Methods

Forty litters (528 piglets) were divided into 4 groups: 1) Control group receiving no MS (CON); 2) MS1 administered automatically (A-MS1); 3) MS1 administered manually (Ma-MS1) 4) MS2 administered manually (Ma-MS2). All groups had access to sow milk and creep feed. On day 5 after birth (d0), litters were equalized (13.2 piglets/litter ± 0.8 SD), thereafter no cross-fostering was allowed. Piglets were weighed at day 5 after birth (d0), at the end of milk supplementation (d14), at weaning (d21 of the trial, 26 days of age) and ten days post-weaning (d31). Piglet welfare was assessed using behavioral and lesion measures at d4 and d10. Feces were collected at d14 and d21.

Results and discussion

During the suckling period, A-MS1 had lowest mortality (p < 0.05), while Ma-MS1 had lower mortality compared with CON and Ma-MS2 (p < 0.05). Negative social behavior at d4, was more frequent in MS groups (A-MS1, Ma-MS1, Ma-MS2) compared to CON group (p = 0.03). Growth performance and lesion prevalence were not affected by MS provision. During lactation, Ma-MS2 group had a higher percentage of piglets not eating during suckling at d18 compared with Ma-MS1 (p = 0.03). MS1 increased microbial diversity compared with CON at d14 (Chao1, p = 0.02; Shannon, p = 0.03) and compared with CON (Shannon, p < 0.05; InvSimpson, p = 0.01) and Ma-MS2 (Chao1, p < 0.05; Shannon, p = 0.05, InvSimpson p = 0.01) at d21. Groups that received MS1 were characterized by genera producing short-chain fatty acids (SCFAs), i.e., Lachnospiraceae (A-MS1) and Oscillospiraceae (Ma-MS1). MS composition and availability can contribute to reduce piglet's mortality during the suckling phase and can also affect intestinal microbiota by favoring the presence of SCFAs producing bacteria.

Metabolic Responses of Dietary Fiber during Heat Stress: Effects on Reproductive Performance and Stress Level of Gestating Sows

Heat stress is an important issue, and the addition of fiber to the diet is an option in modifying intestinal health. This study evaluated the effect of acid detergent fiber (ADF) levels on reproductive performance, intestinal integrity, and metabolism of gestating sows, and its carry-over effect on the lactation period during heat stress. The diets included 4.3% (Low fiber; LF), 5.4% (Medium fiber; MF), and 6.5% (High fiber; HF) ADF. Sows fed the HF diet showed a lower respiratory rate, hair cortisol concentration, and farrowing duration compared with the LF treatment. The HF diet increased the pyruvate, citrate cycle, glyoxylate, dicarboxylate, and thiamine metabolism compared with the MF. The concentration of acetate and total short-chain fatty acids were increased in the sows fed the HF diet. The gene expression of glucose transporter 3 and glucose transporter 4 was increased in the HF treatment. The gene expression of heat shock protein 70 was decreased in the HF treatment. The HF diet during gestation increased feed intake, constipation index, piglet weight, and litter weight compared with the LF. Sows in the LF treatment showed the greatest digestibility of crude protein and the lowest digestibility of ADF. In conclusion, a 6.5% ADF level is recommended for gestating sows during heat stress.

Nutritional Regulation of Mammary Gland Development and Milk Synthesis in Animal Models and Dairy Species

In mammals, milk is essential for the growth, development, and health. Milk quantity and quality are dependent on mammary development, strongly influenced by nutrition. This review provides an overview of the data on nutritional regulations of mammary development and gene expression involved in milk component synthesis. Mammary development is described related to rodents, rabbits, and pigs, common models in mammary biology. Molecular mechanisms of the nutritional regulation of milk synthesis are reported in ruminants regarding the importance of ruminant milk in human health. The effects of dietary quantitative and qualitative alterations are described considering the dietary composition and in regard to the periods of nutritional susceptibly. During lactation, the effects of lipid supplementation and feed restriction or deprivation are discussed regarding gene expression involved in milk biosynthesis, in ruminants. Moreover, nutrigenomic studies underline the role of the mammary structure and the potential influence of microRNAs. Knowledge from three lactating and three dairy livestock species contribute to understanding the variety of phenotypes reported in this review and highlight (1) the importance of critical physiological stages, such as puberty gestation and early lactation and (2) the relative importance of the various nutrients besides the total energetic value and their interaction.

Hydrogen sulfide is a regulator of mammary gland development in prepubescent female mice

The present study aimed to investigate the effects of exogenous H2S on mammary gland development in pubescent mice and to explore the underlying mechanism. The mouse mammary epithelial cell line HC11, along with C57BL/6J mice, were treated with different concentrations of sodium hydrosulfide (NaHS), which is a donor of H2S. The HC11 cell viability, pubescent mammary gland development, and the involvement of proliferative proteins and pathways were assessed by CCK‑8 assay, EdU assay, whole mount staining, H&E staining, western blotting and reverse transcription‑quantitative PCR. Both in vitro and in vivo, a low concentration of NaHS (100 µM in vitro; 9 mg/kg in vivo) significantly promoted the viability of HC11 cells and the development of mammary glands by increasing the expression of the proliferative markers cyclin D1/3 and proliferating cell nuclear antigen. However, a high concentration of NaHS (1,000 µM in vitro; 18 mg/kg in vivo) inhibited HC11 cell viability, mammary gland development and the expression levels of proteins involved in proliferation. Subsequent experiments revealed that NaHS regulated the phosphatidylinositol 3‑kinase (PI3K)/protein kinase B (Akt)‑mammalian target of rapamycin (mTOR) signaling pathway during this process. In vivo, intraperitoneal injection of low concentration NaHS (9 mg/kg) activated the PI3K/Akt‑mTOR pathway in mammary glands of pubescent mice, increased the secretion of insulin‑like growth factor 1 (IGF‑1) and estradiol (E2), and then stimulated mammary gland ductal development. Whereas a high concentration of NaHS (18 mg/kg) elicited the opposite effects to those of low‑dose NaHS. In conclusion, the present study demonstrated that exogenous H2S supplied by NaHS may exert bidirectional effects on mammary gland ductal development; promoting ductal development at a low concentration and inhibiting it at a high concentration. The effects of H2S may occur via the intracellular PI3K/Akt‑mTOR signaling pathway, or by regulation of the secretion of IGF‑1 and E2.

Review: Mammary gland development in swine: embryo to early lactation

Milk production by the sow is a major factor limiting the growth and survival of her litter. Understanding the process of morphogenesis of the sow's mammary gland and the factors that regulate mammary development are important for designing successful management tools that may enhance milk production. Primordia of the mammary glands are first observable in the porcine embryo at approximately 23 days of gestation. The glands then progress through a series of morphologically distinct developmental stages such that, at birth, each mammary gland is composed of the teat, an organized fat pad and two separate lactiferous ducts each with a few ducts branching into the fat pad. The glands continue to grow slowly until about 90 days of age when the rate of growth increases significantly. The increased rate of mammary gland growth coincides with the appearance of large ovarian follicles and an increase in circulating estrogen. After puberty, the continued growth of the gland and elongation and branching of the duct system into the fat pad takes place in response to the elevated levels of estrogen occurring as part of the estrous cycles. After conception, parenchymal mass of each gland increases slowly during early pregnancy and then grows increasingly rapidly during the final trimester. This growth is in response to estrogen, progesterone, prolactin and relaxin. Lobuloalveolar development occurs primarily during late pregnancy. By parturition, the fat pad of the mammary gland has been replaced by colostrum-secreting epithelial cells that line the lumen of the alveoli, lobules and small ducts. All mammary glands develop during pregnancy, however, the extent of development is dependent on the location of the mammary gland on the sow's underline. The mammary glands undergo significant functional differentiation immediately before and after farrowing with the formation of colostrum and the transition through the stages of lactogenesis. Further growth of the glands during lactation is stimulated by milk removal. Individual glands may grow or transiently regress in response to the intensity of suckling during the initial days postpartum. Attempts to enhance milk production by manipulation of mammary development at stages before lactation generally have met with limited success. A more in depth understanding of the processes regulating porcine mammary gland morphogenesis at all stages of development is needed to make further progress.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Mammary growth during pregnancy and lactation and its relationship with milk yield

The number of secretory cells in the mammary gland is often cited as a major determinant of milk production. However, literature data for proxy measures of secretory cell number do not fully support such a claim. In particular, measurements of total mammary DNA in livestock explain only <25% of variation in milk yield, probably because of tissue heterogeneity for DNA concentration. Relative to BW, measurements of udder size in dairy cattle, as total DNA or udder weight, are approximately double those seen in most other livestock classes. Therefore, selection for dairy production, not surprisingly, has resulted in cows with greater secretory capacity. There is limited evidence that genetic selection is still increasing udder size in some cattle populations, but more recent data are needed. It is contended that the most important period of mammary growth for determination of milk yield is that occurring in pregnancy and early lactation. Mammary development is largely complete, at term, in sheep, goats, and cattle, but in pigs, the udder continues to grow during the first 3 wk of lactation, depending, in part, on litter size. Increased litter size in sheep and goats will enhance the extent of mammary development at the end of gestation (and milk yield) by 20 to 25%. However, twinning in dairy cattle does not affect milk production and, by inference only, is not likely to affect numbers of secretory cells at term. Milking frequency and suckling intensity in very early lactation will increase milk yield in cows and increase mammogenesis and milk yield in sheep, indicating that even at term, the ruminant gland retains some capacity for further development, if demand requires it. There is limited understanding of the hormonal signals in pregnancy that regulate mammary development relative to the number of young carried. Furthermore, the genetic differences between dairy and beef cattle that lead to substantially greater udder size in the dairy breeds have not been identified. During lactation, the drivers for secretory cell loss in relation to milking frequency and nutritional status are still not known. Measurement of mammary development and using this phenotype in genomewide association studies to identify key genetic variants for mammogenesis will provide knowledge that is fundamental to understanding the quantitative regulation of milk production.

Exogenous H2 S exerts biphasic effects on porcine mammary epithelial cells proliferation through PI3K/Akt-mTOR signaling pathway

This study aimed to investigate the effects of exogenous H₂ S on the proliferation of porcine mammary gland epithelial cells (PMECs) and explore the underlying mechanisms. We found that exposure of PMECs to NaHS, at concentrations ranging from 10 to 200 µM, stimulated cell proliferation. However, high concentration of NaHS (600 µM) inhibited PMECs proliferation. Accordingly, 10 µM NaHS significantly increased the percentage of cells undergoing DNA replication, elevated the mRNA and/or protein expression of Cyclin A2, Cyclin D1/3, Cyclin E2 and PCNA, and decreased p21 mRNA expression. In contrast, 600 µM NaHS elicited the opposite effects to that of 10 µM NaHS. In addition, PI3 K/Akt and mTOR signaling pathways were activated or inhibited in response to 10 or 600 µM NaHS, respectively. Furthermore, the promotion of PMECs proliferation, the change of proliferative genes expression, and the activation of mTOR signaling pathway induced by 10 µM NaHS were effectively blocked by PI3 K inhibitor Wortmannin. Similarly, inhibition of mTOR with Rapamycin totally abolished the 10 µM NaHS-induced stimulation of PMECs proliferation and alteration of proliferative genes expression, with no influence on PI3 K/Akt signaling pathway. Moreover, constitutive activation of Akt pathway via transfection of Akt-CA completely eliminated the inhibition of PMECs proliferation and mTOR signaling pathway, and the change of proliferative genes expression induced by 600 µM NaHS. In conclusion, our findings provided evidence that exogenous H₂ S supplied by NaHS exerted biphasic effects on PMECs proliferation, with stimulation at lower doses and suppression at high dose, through the intracellular PI3 K/Akt-mTOR signaling pathway.

Transcriptional profiling of swine mammary gland during the transition from colostrogenesis to lactogenesis using RNA sequencing

Background

Colostrum and milk are essential sources of antibodies and nutrients for the neonate, playing a key role in their survival and growth. Slight abnormalities in the timing of colostrogenesis/lactogenesis potentially threaten piglet survival. To further delineate the genes and transcription regulators implicated in the control of the transition from colostrogenesis to lactogenesis, we applied RNA-seq analysis of swine mammary gland tissue from late-gestation to farrowing. Three 2nd parity sows were used for mammary tissue biopsies on days 14, 10, 6 and 2 before (−) parturition and on day 1 after (+) parturition. A total of 15 mRNA libraries were sequenced on a HiSeq2500 (Illumina Inc.). The Dynamic Impact Approach and the Ingenuity Pathway Analysis were used for pathway analysis and gene network analysis, respectively.

Results

A large number of differentially expressed genes were detected very close to parturition (−2d) and at farrowing (+ 1d). The results reflect the extraordinary metabolic changes in the swine mammary gland once it enters into the crucial phases of lactogenesis and underscore a strong transcriptional component in the control of colostrogenesis. There was marked upregulation of genes involved in synthesis of colostrum and main milk components (i.e. proteins, fat, lactose and antimicrobial factors) with a pivotal role of CSN1S2, LALBA, WAP, SAA2, and BTN1A1. The sustained activation of transcription regulators such as SREBP1 and XBP1 suggested they help coordinate these adaptations.

Conclusions

Overall, the precise timing for the transition from colostrogenesis to lactogenesis in swine mammary gland remains uncharacterized. However, our transcriptomic data support the hypothesis that the transition occurs before parturition. This is likely attributable to upregulation of a wide array of genes including those involved in ‘Protein and Carbohydrate Metabolism’, ‘Immune System’, ‘Lipid Metabolism’, ‘PPAR signaling pathway’ and ‘Prolactin signaling pathway’ along with the activation of transcription regulators controlling lipid synthesis and endoplasmic reticulum biogenesis and stress response.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4719-5) contains supplementary material, which is available to authorized users.

Oleic acid stimulates HC11 mammary epithelial cells proliferation and mammary gland development in peripubertal mice through activation of CD36-Ca2+ and PI3K/Akt signaling pathway

This study aimed to investigate the effects of oleic acid (OA), a monounsaturated fatty acid, on HC11 mammary epithelial cells proliferation and peripubertal mammary gland development and explore the underlying mechanisms. HC11 cells and C57BL/6J mice were treated with OA. HC11 proliferation, peripubertal mammary gland development, and the involvement of CD36 and PI3K/Akt were assessed. In vitro, 100 μM OA significantly promoted HC11 proliferation by increasing Cyclin D1/3 and PCNA expression and decreasing p21 expression. Meanwhile, OA enhanced CD36 expression, elevated [Ca²⁺]_i and activated PI3K/Akt signaling pathway. However, knockdown of CD36, chelation of [Ca²⁺]_i or inhibition of PI3K eliminated the OA-induced promotion of HC11 proliferation and change in proliferative markers expression. In vivo, peripubertal exposure to diet containing 2% OA stimulated mammary duct development, with increased terminal duct end (TDE) and ductal branch. Moreover, dietary OA increased the serum levels of IGF-1 and E2, enhanced the expression of CD36 and Cyclin D1, and activated PI3K/Akt pathway in mammary glands. In conclusion, OA stimulated HC11 cells proliferation and mammary gland development in peripubertal mice, which was associated with activation of CD36-[Ca²⁺]_i and PI3K/Akt signaling pathway. These data provided new insights into the stimulation of mammary gland development by dietary oleic acid.

Porcine circovirus type 2 associated reproductive failure in a specific pathogen free (SPF) piglet producing herd in Norway: a case report

BACKGROUND

Since 1999, scientists have published evidence of transplacental infection by porcine circovirus type 2 (PCV2) and reproductive failure in pigs. Affected herds have frequently been start-up herds, either naïve or with a high proportion of PCV2 susceptible gilts. Here, delayed farrowing in non-vaccinated gilts was observed in a commercial specific pathogen free (SPF) herd. Mummified fetuses and stillborn piglets recovered from these gilts were PCV2 positive.

CASE PRESENTATION

The case herd was a self-recruiting, piglet producing unit of 240 sows. After detecting livestock associated methicillin resistant Staphylococcus aureus (LA-MRSA, CC398), stamping out was imposed by the authorities. An SPF herd was re-established and all dams were vaccinated against PCV2 until the farmer decided to exclude this vaccine. The first non-vaccinated batch consisted of 76% gilts. Here, one gilt showed signs of impending farrowing. This gilt was slaughtered three to four weeks after the expected farrowing date without having expelled any uterine contents. In the subsequent batch consisting of 79% gilts, three gilts showed similar clinical signs. Delayed farrowing was observed in two of these gilts and the uterine contents from the third gilt were recovered at the abattoir. Mummified fetuses and stillborn piglets were recovered from all three gilts. High levels of PCV2 DNA (>10⁷ viral genomic copies/ 500 ng tissue) were found in myocardial samples by real-time PCR analysis. One myocardial sample submitted for immunohistochemical (IHC) analysis showed moderate amounts of PCV2 antigen. In the subsequent batch consisting of 77% gilts, several weak-born piglets were seen across different litters.

CONCLUSIONS

This case report describes an apparent link between in utero PCV2 infection, pre partum nest-building behaviour, mammary development and delayed farrowing. To date, no reports have described imminent signs of farrowing and delayed farrowing as clinical signs in conjunction with transplacental PCV2 infection in Norway. Reinitiation of PCV2 vaccination was strongly advised in this herd due to recent depopulation and repopulation and the high proportion of gilts. Vaccination was effective because no further cases have occurred since.

Stearic acid suppresses mammary gland development by inhibiting PI3K/Akt signaling pathway through GPR120 in pubertal mice

It has been demonstrated that dietary high fat diet negatively affects the pubertal mammary gland development. The aim of the present study was to investigate the effects of stearic acid (SA), an 18-carbon chain saturated fatty acid, on mammary gland development in pubertal mice and to explore the underlying mechanism. Our results demonstrated that dietary supplementation of 2% SA suppressed mammary duct development, with significant reduction of terminal end bud (TEB) number and ductal branch. In accord, the expression of proliferative marker Cyclin D1 was markedly decreased by dietary SA. Furthermore, dietary SA led to increase of G protein-coupled receptor 120 (GPR120) expression and inhibition of PI3K/Akt signaling pathway in mammary gland of pubertal mice. In good agreement with the in vivo findings, the in vitro results showed that 40 μM SA significantly suppressed proliferation of mouse mammary epithelial cell HC11 by regulating mRNA and/or protein expression of proliferative markers such as Cyclin D1/3, p21, and PCNA. Meanwhile, SA activated GPR120 and inhibited PI3K/Akt signaling pathway in a GPR120-dependent manner. In addition, SA-induced inhibition of PI3K/Akt signaling pathway, suppression of HC11 proliferation, and alteration of proliferative markers expression were abolished by knockdown of GPR120 with siRNA. Collectively, these findings showed that SA suppressed mammary gland development of pubertal mice, which was coincident with the SA-inhibited HC11 proliferation, and was associated with inhibition of PI3K/Akt signaling pathway through activation of GPR120. These data provided new insights into the regulation of mammary gland development by dietary fatty acids.

Lauric Acid Stimulates Mammary Gland Development of Pubertal Mice through Activation of GPR84 and PI3K/Akt Signaling Pathway

It has been demonstrated that dietary fat affects pubertal mammary gland development. However, the role of lauric acid (LA) in this process remains unclear. Thus, this study aimed to investigate the effects of LA on mammary gland development in pubertal mice and to explore the underlying mechanism. In vitro, 100 μM LA significantly promoted proliferation of mouse mammary epithelial cell line HC11 by regulating expression of proliferative markers (cyclin D1/3, p21, PCNA). Meanwhile, LA activated the G protein-coupled receptor 84 (GPR84) and PI3K/Akt signaling pathway. In agreement, dietary 1% LA enhanced mammary duct development, increased the expression of GPR84 and cyclin D1, and activated PI3K/Akt in mammary gland of pubertal mice. Furthermore, knockdown of GPR84 or inhibition of PI3K/Akt totally abolished the promotion of HC11 proliferation induced by LA. These results showed that LA stimulated mammary gland development of pubertal mice through activation of GPR84 and PI3K/Akt signaling pathway.

Effect of feeding liquid milk supplement on litter performances and on sow back-fat thickness change during the suckling period

Abstract. The aim of the present study was to investigate the effect of liquid milk supplement on litter performance (weight development of the piglets, weaning weight and mortality) and on sow back-fat thickness change during the suckling period. Data were collected from 150 litters, with the weight of a total of 1709 piglets measured at birth, at 14 days of age and at weaning (28 days), respectively. Sow (n = 150) back-fat depth was measured the day before farrowing, 14 days after farrowing and at weaning. In the control group (n = 363), the piglets were suckled and got pre-starter feed from day 10. In the four experimental groups (MS1; MS2; MS2 and MS4; n = 1346), the piglets received additional milk replacer in various concentrations from the 10th day of life. While there were no significant differences in birth weight between the control and experimental groups, we did find significant differences between the 14-day weights and weaning weights. The milk supplement significantly reduced mortality compared to the control (11.6 vs. 4.9; 5.9, 8.9; 8.3 %). However, there were no statistically significant differences between litter homogeneity data, based on the CV% of piglet weight. Three experimental groups (MS1, MS2 and MS4) were more homogenous compared to the control group at weaning (25.3 vs. 20.9; 20.3; 20.3 CV%). Based on the examination of sow back-fat thickness reduction, there were significant differences between the control (C) and MS3 groups (7.61 vs. 5.57 mm reduction, P < 0.05) during the suckling period. These results demonstrate the advantage of milk replacer on weaning weight. Litter homogeneity, piglet mortality and back-fat thickness of the sows were affected by providing milk replacer to the piglets during the suckling period.