Follicular development during early pregnancy and the estrous cycle of the sow

Follicle development in pigs: State of the art

Understanding the factors and pathways involved with recruitment, atresia, and selection of follicles in the pig, may provide insight into approaches to limit fertility failures. Antral follicles depend upon FSH to the 2-3 mm stage, become codependent upon LH at 4-5 mm, and rely on LH when >5 mm. Within the follicle, gonadotropin binding, steroids, growth factors, and inhibin interact to determine the fate of the follicle. Continuous recruitment appears likely for follicles, and once >1 mm, they may have a limited period for survival, before selection or atresia. If true, then the number of healthy follicles that can respond to a hormone signal for selection, could vary by size and development stage. Which follicles are selected may depend upon their age, numbers of capillaries, granulosa and thecal cells, and FSH and LH receptors. This might also suggest that factors such as management, nutrition, and stress in prior weeks, could affect different cohorts of follicles to determine which of those from the ovarian population will be selected.

Comparison between transrectal palpation, B-mode and Doppler ultrasonography to assess luteal function in Holstein cattle

Introduction

Over the years, the most common methods for monitoring reproductive health in cattle have varied from transrectal palpation to B-mode ultrasonography. Nowadays, some portable ultrasound equipment includes the Doppler mode. Therefore, the aim of this study was to compare the accuracy of the different methods to assess corpus luteum (CL) functionality.

Methods

In Experiment 1, 53 Holstein lactating cows undergoing a synchronization protocol were examined via transrectal palpation and B-mode scanning. Measurements for the largest diameter (LAD) and subjective size of CL (SCLS) were collected. Data were analyzed using correlation analysis and ROC Curves. In Experiment 2, 30 Holstein non-lactating cows with a CL were administered PGF2α and examined several times after injection, first in B-mode and then with Power Doppler. Measurements for LAD, CL area (CLA) and subjective and objective CL blood flow were collected. Blood samples were taken in both experiments to determine P4 concentration. Data were analyzed using correlation analysis and the GLM repeated measures test.

Results

Results for Experiment 1 showed that LAD was more accurate than SCLS. In Experiment 2, CLA was the best measurement to assess CL function, although both subjective and objective CL blood flow offer accurate information 24 h after PGF2α administration.

Discussion

Consequently, ultrasonography provides more accurate information about CL function than transrectal palpation. Although CLA seems to be an earlier indicator of luteal function than blood flow, 24 h after the onset of luteolysis, both parameters are valid.

The effect of electromagnetic field (EMF) exposure on synthesis and release of steroid hormones by the porcine conceptuses during the peri-implantation period

CONTEXT

Electrical devices and power systems are the sources of EM-waves which propagate everywhere in the environment.

AIMS

The study aimed to determine whether EMF induced changes in the steroidogenesis of conceptuses and whether progesterone (P4 ) may be a possible protectant against the effects of EMF radiation.

METHODS

The entire porcine conceptuses were collected during the peri-implantation period (days 15-16 of pregnancy), divided into fragments (100mg) and treated in vitro with EMF (50Hz or 120Hz, 2 or 4h exposure), and examined to determine of CYP17A1 , HSD3B1 , CYP19A3 , and HSD17B4 mRNA transcript and encoded protein abundance and the release of steroid hormones. Selected fragments of conceptuses were treated with P4 .

KEY RESULTS

In conceptuses incubated without P4 , EMF at 120Hz decreased androstenedione (A4 ) and testosterone (T) release after 2h and increased oestrone (E1 ) release at 50Hz and 120Hz after 4h exposure. In P4 -treated conceptuses, EMF (50 and 120Hz, 4h exposure) decreased CYP19A3 mRNA transcript abundance, and increased (120Hz, 2h exposure) oestradiol-17β (E2 ) release.

CONCLUSIONS

The EMF radiation alters androgen and oestrogen synthesis and release from the conceptuses of pigs during the peri-implantation period. The P4 exerts protective effects on androgens and E1 release but it sensitises the conceptuses when comes to the mechanism of oestrogen synthesis and release during EMF radiation.

IMPLICATIONS

The effect of EMF radiation on the steroidogenic pathway in conceptuses may induce disturbances in their proper development and implantation.

Electromagnetic field exposure alters in vitro estrogen biosynthesis and its release by the porcine endometrium in the peri-implantation period

The electromagnetic field (EMF) is an environmental risk factor that may impair living organisms. This study aims to determine the functional effects of EMF exposure at 50 and 120 Hz for 2 or 4 h on estrogen synthesis and release in the endometrium. Endometrial slices were isolated from pigs (n = 5) during the peri-implantation period. To check whether progesterone (P₄) exerts any protective effects against EMF, selected EMF-treated slices were also treated with P₄. CYP19A3 mRNA transcript abundance was higher in slices exposed to EMF (50 Hz, 4 h) and treated with P₄. HSD17B4 mRNA transcript abundance was higher in slices exposed to EMF (50 and 120 Hz, 2 h) without P₄ treatment. Both EMF (50 Hz, 2 h) and EMF (50 and 120 Hz, 4 h) increased HSD17B4 mRNA transcript abundance in the presence of P₄; EMF (120 Hz, 2 h, and 50 Hz, 4 h) decreased cytochrome P-450arom protein abundance in tissue slices not treated with P₄. Under exposure to EMF at 120 Hz (2 h), the abundance of hydroxysteroid 17β dehydrogenase decreased in P₄-treated slices and increased in slices not treated with P₄ (4 h). Progesterone treatment decreased the release of estradiol-17β (E₂) in endometrial slices exposed to EMF at 50 Hz (2 h), whereas in slices not treated with P₄, EMF (120 Hz, 2 h) increased estrone (E₁) release compared to control (without EMF). The EMF could disrupt the synthesis and release of E₁ and E₂ by the porcine endometrium during the peri-implantation period.

Nutritional restriction during the peri-conceptional period alters the myometrial transcriptome during the peri-implantation period

This study hypothesized that female peri-conceptional undernutrition evokes transcriptomic alterations in the pig myometrium during the peri-implantation period. Myometrium was collected on days 15-16 of pregnancy from pigs fed a normal- (n = 4) or restricted-diet (n = 4) from conception until day 9th of pregnancy, and the transcriptomic profiles of the tissue were compared using Porcine (V2) Expression Microarrays 4 × 44 K. In restricted diet-fed pigs, 1021 differentially expressed genes (DEGs) with fold change ≥ 1.5, P ≤ 0.05 were revealed, and 708 of them were up-regulated. Based on the count score, the top within GOs was GO cellular components "extracellular exosome", and the top KEGG pathway was the metabolic pathway. Ten selected DEGs, i.e. hydroxysteroid (17β) dehydrogenase 8, cyclooxygenase 2, prostaglandin F receptor, progesterone receptor membrane component 1, progesterone receptor membrane component 2, annexin A2, homeobox A10, S-phase cyclin A-associated protein in the ER, SRC proto-oncogene, non-receptor tyrosine kinase, and proliferating cell nuclear antigen were conducted through qPCR to validate microarray data. In conclusion, dietary restriction during the peri-conceptional period causes alterations in the expression of genes encoding proteins involved i.a. in the endocrine activity of the myometrium, embryo-maternal interactions, and mechanisms regulating cell cycle and proliferation.

Follicular waves in ontogenesis and female fertility

Antral follicle growth and recruitment are the basis of female reproduction. Follicular wave theory explains the recruitment, growth, and selection of antral follicles. This article is devoted to the follicular wave pattern in female reproduction throughout life. We highlight progress in understanding the rhythmic follicle changes based on clinical studies and studies on animal models. We review the follicular wave pattern before puberty, during pregnancy, and in perimenopause. Several mathematical models are known which quite accurately describe follicular wave dynamics. The follicular waves theory allows the implementation of the new approaches to ovarian stimulation. Stimulation in the luteal phase and double stimulation are used more widely nowadays for fertility preservation in cancer patients and for increasing the chances of IVF programs success in poor responder patients.

Effects of LH and FSH on androgen and oestrogen release in the myometrium of pigs during the oestrous cycle and early pregnancy

The porcine myometrium possesses steroidogenic activity. LH and FSH are hypothesised to regulate the myometrial production of androstenedione (A4), testosterone (T), oestrone (E1) and 17β-oestradiol (E2). In this study, we used myometrium collected from cycling (n=15) and pregnant (n=15) pigs on Days 10-11, 12-13 and 15-16 of the oestrous cycle or pregnancy to determine: (1) the abundance of LH and FSH receptor (LH/choriogonadotrophin receptor (CGR) and FSHR) mRNA and protein; (2) activity of 17β-hydroxysteroid dehydrogenase 1 (17βHSD1); and (3) A4, T, E1 and E2 release in response to LH and FSH treatment, used at doses 10 or 100ng mL-1 for 6h. In results, the myometrium possesses LH/CGR and FSHR with minor alterations in their expression in the course of the oestrous cycle or early pregnancy. 17βHSD1 activity was the highest on Days 12-13 of the oestrous cycle and the lowest on Days 15-16 of the oestrus cycle and pregnancy, when compared to the other studied days of the oestrous cycle or pregnancy. The LH and FSH treatment increased A4 release on Days 12-13 of the oestrous cycle, and E1 and E2 release on Days 15-16 of the oestrous cycle. Moreover, on Days 12-13 E2 release was increased in response to FSH treatment (100ng mL-1) in cycling pigs and in response to LH (100ng mL-1) in pregnant pigs. In conclusion, the myometrium of pregnant and non-pregnant pigs expresses LH/CGR and FSHR and has 17βHSD1 activity. In addition, the amount of A4, E1, and E2 release from the myometrium is altered in response to LH and FSH, especially in cycling pigs. LH and FSH appear to be important regulators of myometrial oestrogen release in pigs mostly during luteolysis.

Effect of kisspeptin (KISS) and RFamide-related peptide-3 (RFRP-3) on the synthesis and secretion of FSH in vitro by pituitary cells in pigs

Kisspeptins (KISSs) and RFamide-related peptide-3 (RFRP-3) affect the synthesis and secretion of luteinizing hormone (LH) and modulate female reproductive processes. The presence of KISS and RFRP-3 in the porcine pituitary gland and their contribution to the regulation of follicle-stimulating hormone (FSH) synthesis and secretion is unknown. This study analyzed the presence of KISS and RFRP-3 in the pituitary of estrous-cyclic pigs on days 2 to 3, 10 to 11, 12 to 13, 15 to 16 and 19 to 20 and early pregnant pigs on days 10 to 11, 12 to 13 and 15 to 16, and evaluated the effect of KISS and RFRP-3 on β-Fsh mRNA expression and FSH secretion in vitro by pituitary cells collected on selected days of the estrous cycle. The cells were cultured in vitro and treated with KISS (10^-6 M, 10^-7 M) and RFRP-3 (10^-6 M, 10^-7 M) or gonadotropin-releasing hormone (GnRH; 100 ng/mL) alone and in combinations (4 h or 24 h). The relative abundance of Kiss and Rfrp-3 and their receptor mRNA transcripts, as well as the KISS and RFRP-3 proteins, were found in the pituitaries of estrous-cyclic and early pregnant pigs. KISS after 4 h increased the secretion of FSH in estrous cyclic pigs mostly during the early-luteal phase and luteolysis. RFRP-3 inhibited the synthesis and secretion of FSH in estrous-cyclic pigs on days 19 to 20 and the secretion of FSH on days 2 to 3 and 10 to 12 of the estrous cycle compared with GnRH-treated cells. KISS in co-treatment with GnRH after 24 h enhanced FSH release on days 2 to 3 and 15 to 16 of the estrous cycle. In conclusion, KISS and RFRP-3 systems are present in the pituitary of estrous-cyclic and pregnant pigs. In estrous-cyclic pigs, KISS and RFRP-3 may affect the synthesis and secretion of FSH by pituitary cells.

Electromagnetic Field (EMF) Radiation Alters Estrogen Release from the Pig Myometrium during the Peri-Implantation Period

An electromagnetic field (EMF) may affect the functions of uterine tissues. This study hypothesized that EMF changes the estrogenic activity of pig myometrium during the peri-implantation period. Tissue was collected on days 15-16 of the gestation and incubated in the presence of EMF (50 and 120 Hz, 2 and 4 h). The cytochrome P450 aromatase type 3 (CYP19A3) and hydroxysteroid 17β dehydrogenase type 4 (HSD17B4) mRNA transcript abundance, cytochrome P450arom (aromatase), and 17β hydroxysteroid dehydrogenase 17βHSD) protein abundance and estrone (E₁) and estradiol-17β (E₂) release were examined using Real-Time PCR, Western blot and radioimmunoassay. Selected myometrial slices were treated with progesterone (P₄) to determine whether it functions as a protector against EMF. CYP19A3 mRNA transcript abundance in slices treated with EMF was less at 50 Hz (2 h) and greater at 120 Hz (2 and 4 h). HSD17B4 mRNA transcript was greater in slices treated with EMF at 120 Hz (2 h). Progesterone diminished EMF-related effects on CYP19A3 and HSD17B4. When P₄ was added, EMF had suppressive (50 and 120 Hz, 2 h) or enhancing (50 Hz, 4 h) effects on aromatase abundance. The E₁ release was lower after 4 h of EMF treatment at 50 Hz and P₄ did not protect myometrial E₁ release. In conclusion, EMF alters the synthesis and release of E₁ and did not affect E₂ release in the myometrium during the peri-implantation period.

Effects of electromagnetic field (EMF) radiation on androgen synthesis and release from the pig endometrium during the fetal peri-implantation period

An electromagnetic field (EMF) may have effects on female reproduction. This study was conducted to determine whether EMF [50 and 120 Hz, 2 and 4 h of incubation in the presence or absence of progesterone (P₄, 10^-5 M)] affects androgen synthesis and release from the pig endometrium. Endometrial slices were collected from pigs (n = 5) during the fetal peri-implantation period (i.e., days 15-16 of gestation) and treated in vitro with EMF. The selected endometrial slices were treated with P₄ to determine whether this hormone has effects on protection of the tissue from EMF radiation. The CYP17A1 and HSD3B1 mRNA transcript abundance, steroid 17αhydroxylase/17, 20-lyase (cytochrome P450c17) and hydroxyΔ5steroid dehydrogenase/3β and steroidΔisomerase (3βHSD) protein abundance were examined using Real-Time PCR and Western Blot procedures, respectively. In media collected after incubation, the concentrations of androstenedione (A₄) and testosterone (T) were quantified used a RIA. When P₄ was added to the culture medium, EMF radiation had suppressive effects on endometrial T release after 2 and 4 h of incubation when the EMF treatment was occurring and increased A₄ release after 4 h of incubation with EMF at 120 Hz. When there was no inclusion of P₄, release of A₄ was decreased after 2 h of EMF treatment at 120 Hz and after 4 h of EMF treatment at 50 and 120 Hz. Progesterone did not have functions that protected the pig endometrium against EMF radiation during the fetal peri-implantation period.

Consequences of electromagnetic field (EMF) radiation during early pregnancy - androgen synthesis and release from the myometrium of pigs in vitro

An electromagnetic field (EMF) has been found to affect reproductive processes in females. The aim of this study was to determine the effect of low, non-ionizing EMF radiation on the steroidogenic activity of myometrium collected from pigs during the fetal peri-implantation period. Myometrial slices were treated with an EMF (50 and 120 Hz, 2 and 4 h of incubation) and examined for the aromatase cytochrome P450 17α-hydroxylase/C17-20lyase (CYP17A1) and 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (HSD3B1) mRNA transcript abundance, cytochrome P450c17 and 3βHSD protein abundance and the secretion of androstenedione (A₄) and testosterone (T). To determine whether progesterone (P₄) functions as a protectant from EMF radiation, the selected slices were treated with P₄. In slices incubated without P₄, EMF at 50 Hz altered cytochrome P450c17 protein abundance (4 h), HSD3B1 mRNA transcript abundance (4 h) and A₄ release (2 h) as well as T release (2 h) in P₄-treated slices. The EMF at 120 Hz in non P₄-treated slices altered A₄ release (2 and 4 h) whereas in P₄-treated slices altered CYP17A1 mRNA transcript abundance (4 h), 3βHSD protein abundance (4 h), A₄ (4 h) and T release (2 h). In conclusion, EMF radiation in the myometrium collected during the peri-implantation period alters the CYP17A1 and HSD3B1 mRNA transcript and encoded protein abundance, and androgen release due to the time of treatment and P₄ presence or absence. The P₄ did not function directly as an obvious protector against EMF radiation in the myometrium of pigs during the fetal peri-implantation period.

Human chorionic gonadotrophin in early gestation induces growth of estrogenic ovarian follicles and improves primiparous sow fertility during summer

Reduced summer farrowing rates may be due to inadequate corpora luteal (CL) support. Porcine CL become dependent on LH from 12 d of pregnancy and the embryonic estrogen signal for maternal recognition of pregnancy (MRP) is initiated at about 11-12 d after insemination. We hypothesised that injection of the LH analogue human chorionic gonadotropin (hCG) would induce growth of estrogenic follicles and, by mimicking the signal for MRP and stimulating progesterone secretion, increase primiparous sow fertility. In Experiment 1, during a 28 d lactation 53 mixed parity sows were full-fed either throughout lactation (n=16) or until 18 d and then feed restricted during the last 10 d of lactation (n=36). At 12 d after mating restrict-fed sows were injected with 1000IU hCG (n=17) or were not injected (n=19); the full-fed sows acted as non-treated positive controls. Transrectal ovarian ultrasound exams were performed on days 12, 16, 20, 24, and 28; blood samples were obtained on days 12, 14, and 15 for estradiol and progesterone assay. For Experiment 2, during the summer months primiparous sows received 1000IU hCG 12 d after mating (n=28) or were non-injected controls (n=27). Pregnancy status was determined at 28 d and sows allowed to go to term to determine farrowing rates and litter sizes. In Experiment 1, injection of hCG increased (P<0.001) follicle diameter and serum concentrations of estradiol (P<0.01) and progesterone (P<0.05). There were no effects of lactation feeding level on wean-estrus interval, farrowing rate or subsequent litter size. In Experiment 2, hCG injection was associated with a higher pregnancy rate (P<0.05) and farrowing rate (P<0.08). There was no effect on litter size. These data confirm that hCG stimulates growth of estrogenic follicles and CL function, and improves primiparous sow fertility during the summer months.

How ultrasound technologies have expanded and revolutionized research in reproduction in large animals

Gray-scale ultrasonic imaging (UI) was introduced in 1980 and initially was used to examine clinically the reproductive tract of mares. By 1983 in mares and 1984 in heifers/cows, UI had become a tool for basic research. In each species, transrectal gray-scale UI has been used extensively to characterize follicle dynamics and investigate the gonadotropic control and hormonal role of the follicles. However, the use of transrectal UI has also disclosed and characterized many other aspects of reproduction in each species, including (1) endometrial echotexture as a biological indicator of circulating estradiol concentrations, (2) relative location of the genital tubercle for fetal gender diagnosis by Days 50 to 60, and (3) timing of follicle evacuation during ovulation. Discoveries in mares include (1) embryo mobility wherein the spherical conceptus (6-16 mm) travels to all parts of the uterus on Days 11 to 15, (2) how one embryo of a twin set eliminates the other without self-inflicted damage, and (3) serration of the granulosum of the preovulatory follicle opposite to the future rupture site as an indicator of imminent ovulation. Studies with color-Doppler UI have shown that vascular perfusion of the endometrium follows the equine embryo back and forth between uterine horns and follows the expansion of the bovine allantochorion throughout each horn. In heifers, blood flow in the CL increases during the ascending portion of an individual pulse of PGF2α metabolite and then decreases. These examples highlight the power of UI in reproduction research. Without UI, it is likely that these and many other findings would still be unknown.

Follicle Development during Luteal Phase and Altrenogest Treatment in Pigs

Synchronization of the oestrous cycle of gilts using altrenogest treatment has been found to increase ovulation rate. The current experiment investigated if the increase in ovulation rate after altrenogest treatment is related to increased follicle size at the end of altrenogest treatment compared with late luteal phase follicles. Crossbred gilts (n = 15) received altrenogest during 18 days [20 mg Regumate (Janssen Animal Health, Beerse, Belgium)], starting 5-7 days after onset of first oestrus. Control gilts (n = 15) did not receive altrenogest. At days 10-12 of the oestrous cycle [i.e. in the presence of corpora lutea (CL)], average follicle development was 2.51 +/- 0.20 mm (assessed with ultrasound) in altrenogest-treated gilts and 2.58 +/- 0.16 mm in control gilts (p > 0.10). During the last days of altrenogest treatment (i.e. when CL had gone into regression), average follicle size had increased to 3.01 +/- 0.31 mm (p < 0.05). Subsequent ovulation rate was 16.6 +/- 1.7 in altrenogest treated gilts and 15.1 +/- 1.2 in control gilts (p < 0.05). Altrenogest treatment resulted in increased follicle size after regression of the CL, showing that suppression of follicle growth by altrenogest alone is less severe than suppression by endogenous progesterone (either with or without altrenogest). Altrenogest treatment also resulted in a higher ovulation rate. However, it is unclear if the increased follicle size and higher ovulation rate after altrenogest treatment are causally related, as the relation between the two on an animal level was not significant.

Recruitment and selection of ovarian follicles for determination of ovulation rate in the pig

Gonadotropins determine the follicle selection and ovulation rate. Follicle growth is independent of gonadotropins until antrum formation, at which time recruitment occurs. Once recruited, follicles will continue to grow or degenerate. In gilts, visible surface follicles are classified as small (<3mm), medium (3-6.9 mm) and large (> or =7.0mm). At estrus (day 0), there are approximately 15 small and medium follicles, and approximately 15 large follicles. By day 3, there may be approximately 30 small, 5 medium and no large follicles. During the remainder of the luteal phase, the pool of follicles increases and peaks at day 11-13 with approximately 50 small, and 30 medium, but with no large follicles observed. By the start of the follicular phase at day 15, numbers of small and medium follicles rapidly decline, while a pool of medium follicles is selected for the ovulation. The size of large follicles at estrus is heterogeneous (6.5-10.0 mm) but their number is reflective of the subsequent number of corpora lutea found following the ovulation. However, the time of medium follicle selection for ovulation is variable during the late luteal and early follicular phases. Suppression of FSH before and at the time of luteolysis reduces medium and large follicles but does not reduce the ovulation rate. In contrast, suppression of FSH for 3 days or unilateral ovariectomy after 3 days of the follicular phase prevents full ovulatory compensation. Therefore, FSH appears to be involved in the maintenance of a pool of medium follicles that can be selected by LH to mature and ovulate.

Development of a method of diagnosing ovarian disorders in sows and gilts using uterine ultrasonography

In ultrasonographic diagnosis of ovarian disorders and the estrous cycle in sows, transverse observation of the uterus yielded more characteristic findings than observation of sagittal sections. Transverse ultrasonography revealed that the low progesterone (P) type uterus showed a round structure, while the high P type uterus showed a flattened structure. These results corresponded well with rectal palpation findings: the low P type uterus had a hard, pipe-like structure and the high P type a soft, balloon-like structure. For gilts, we employed a minimum convex type transrectal prostate probe that had an approximately 18 cm insertion handle. The images of the uterus obtained thereby were a similar to those obtained from sows. The above results suggest that it should be possible to diagnose and treat many ovarian disorders in sows and gilts based only on the ultrasonograhic findings. In short, ultrasonograhic findings of a round structure of the uterine wall might be an indication for PMSG (pregnant mare serum gonadotropin) treatment, while findings of a flattened structure might be an indication for PGF(2) (alpha) administration.