Aberrant effects of altrenogest and exposure to exogenous gonadotropins on follicular cysts appearance in gilts

Reproductive performance in gilts submitted to non-steroidal therapies to prolong the luteal phase of the estrous cycle

Synchronized cyclicity of replacement gilts is crucial to optimize breeding herd management, however, protocols with oral progestogen are expensive and require daily administration. This study tested two synchronization protocols without progestogens during the luteal phase in gilts. In Experiment I, on the day of the expression of the third estrus (D0), gilts were assigned to three groups (n = 6, each): control, with no treatment; PGF25: in which gilts received two doses of hCG (1,500 IU each) on D12 and D15 and two doses of a prostaglandin F2α (PGF) analogue (sodium cloprostenol; 250 µg) 6-h apart, on D25; and PGF30: in which gilts received two doses of hCG (1,500 IU each) on D12 and D15 and two doses of the PGF analogue (sodium cloprostenol; 250 µg) 6-h apart, on D30. The interval between PGF treatment and estrus expression was shorter in PGF30 than in PGF25 (P < 0.01). The PGF treatment failed to decrease serum progesterone (P4) for gilts from the PGF25 group (P > 0.05), but it was effective for gilts in the PGF30 group (P = 0.01). In Experiment II, gilts were assigned to three groups (n = 12, each): control (no treatment); eCG+hCG (400 IU eCG on D10 plus 500 IU hCG on D12); and hCG2 (two hCG doses, 1,500 IU each on D12 and D15). On D30, gilts from eCG+hCG and hCG2 that did not express estrus received two doses of the PGF analogue (250 µg each, 6-h apart). All gilts were inseminated when estrus was detected. Serum P4 concentrations were similar for all groups on D10 (P > 0.05) and greater on D20 and D25 for gilts in eCG+hCG and hCG2 (P < 0.01) than for those in the control, whereas P4 concentration was greater in hCG2 than in eCG+hCG, on both moments. The inter-estrus interval (IEI) was shorter for control gilts and intermediate for gilts in eCG+hCG, while the longest IEI was observed for gilts in hCG2 (P < 0.01). Total litter size was larger for gilts in the control (P = 0.02) compared to those in hCG2 and did not differ from the other groups for gilts in eCG+hCG (P > 0.05). In conclusion, Experiment I showed that PGF treatment did not induce luteolysis 10 days after the second hCG treatment but it was effective 15 days after the second hCG application. Additionally, Experiment II showed that both eCG+hCG and hCG2 were efficient in prolonging the luteal phase; however, number of piglets born alive and total litter size were negatively affected by the hCG2 protocol. In this sense, treatment with eCG+hCG or hCG2 may represent a steroid-free approach to prolong the luteal phase in gilts, although the doses and number of treatments must be further investigated.

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.

Atretic preovulatory follicles could be precursors of ovarian lutein cysts in the pig

Ovarian cysts contribute to reduced reproductive performance in pigs. Unfortunately, the mechanism of lutein cysts formation remains unknown. Here, we compared the endocrine and molecular milieus of intact, healthy preovulatory follicles (PF), gonadotropin (eCG/hCG)-induced healthy and atretic-like PF, as well as gonadotropin-provoked and spontaneous ovarian cysts in gilts. Several endocrine and molecular indicators and microRNA were compared in walls of PF and cysts. Intact and healthy PF, showed high estradiol/androstendione and low progesterone levels associated with CYP17A1, HSD17B1, and CYP19A1 elevation and reduced StAR/HSD3B1 protein expression. In contrast, low estradiol/androstendione and high progesterone concentrations, accompanied by decreased CYP17A1, HSD17B1, CYP19A1 and increased HSD3B1 protein abundance, appeared in atretic-like PF, gonadotropin-induced and spontaneous cysts. High progesterone receptor (PGR) protein abundance was maintained in intact and healthy PF, while it dropped in atretic-like PF, gonadotropins-induced and spontaneous cysts. The atretic PF showed high level of TNFα compared to healthy PF. In conclusion, follicular lutein cysts could be recruited from atretic-like PF with lost estrogenic milieu and inability to ovulate. Ovulatory cascade was presumably disrupted by a low PGR and high TNFα levels associated with earlier luteinization of follicular walls. These results suggest a novel mechanism of lutein ovarian cysts development in pigs and, perhaps, other species.

Attainment of Sexual Maturity and Gonadotropin Priming in Gilts Determine Follicular Development, Endocrine Milieu and Response to Ovulatory Triggers

The routine procedure of estrous cycle synchronization in pigs allows for the use of gonadotropins to stimulate ovarian activity. The applied protocols of eCG and hFSH priming similarly affected development of ovarian follicles in two classes 3−6 mm and >6 mm of diameter, however, the number of small follicles (<3 mm) was 2-fold higher in hFSH- than in eCG-primed prepubertal gilts. The attainment of sexual maturity increased concentration of estradiol, testosterone and androstenedione in the follicular fluid of hFSH/eCG-primed gilts, however, prostaglandin E2 and F2α metabolite increased in mature hFSH- and eCG-primed gilts, respectively. The maturity increased mRNA and/or protein expression of key steroidogenic enzymes, prostaglandin synthases or luteinizing hormone receptors in follicular walls. Both hormonal primers played a moderate role in affecting expression of steroidogenic enzymes in follicular walls. In vitro studies showed higher estradiol production in r-hLH (p = 0.04)- and r-hCG (p = 0.049)-stimulated follicular walls of mature gilts than in prepubertal hFSH-primed gilts. Both ovulatory triggers decreased the abundance of LHCG/FSH mRNA receptors in follicular walls, which mimic downregulation of these receptors by a preovulatory LH surge, confirmed in vivo. These data revealed the importance of sexual maturity in the protection of the estrogenic environment, and the selective, moderate role of eCG and FSH in the activation of steroidogenic enzymes in preovulatory follicles.

A Short-Term Altrenogest Treatment Post-weaning Followed by Superovulation Reduces Pregnancy Rates and Embryo Production Efficiency in Multiparous Sows

Although embryo transfer (ET) is a biotechnology ready for the swine industry, there are factors to be solved, the availability of embryo donors as one. Multiparous sows as donors ought to be considered since weaning is a natural and efficient method for estrus synchronization. In addition, superovulation treatments at weaning are effective in increasing the efficiency of donor embryo production. However, ET programs typically require more donors than those available from a single weaning, imposing grouping several weanings to establish a batch for ET. Since short-term administration of Altrenogest is effective in delaying estrus after weaning without effects on ovulation and embryo development, we investigated how Altrenogest combined with superovulation would affect reproductive parameters and embryo quality and quantity of weaned multiparous donor sows. The sows were administered Altrenogest from the day of weaning for 14 (SS-14 group; N = 26), 7 (SS-7 group; N = 31) and 4 (SS-4 group; N = 32) days. The sows were superovulated with eCG 24 h after the last administration of Altrenogest and with hCG at the onset of estrus. Sows not treated with Altrenogest that were superovulated with eCG 24 h post-weaning and hCG at the onset of estrus (SC group; N = 37) and sows with natural estrus after weaning (C group; N = 34) were used as control groups. The percentage of sows showing estrus within 10 days was not affected by the treatment, but the interval from Altrenogest withdrawal to estrus was longer (P < 0.05) in the SS groups than the interval from weaning to estrus in the controls. SS treatments increased (P < 0.05) the percentage of sows with ovarian cysts and the development of polycystic ovaries. The pregnancy and the fertilization rates, and the overall embryo production efficiency were also negatively affected by the SS treatments (P < 0.05). Interestingly, almost 70% of the structures classified as unfertilized oocytes or degenerated embryos in sows from the SS groups were immature oocytes. In conclusion, although superovulation of weaned sows was highly efficient, short-term administration of Altrenogest in combination with superovulation had negative effects on most of the reproductive parameters assessed, particularly affecting the overall efficiency of pregnancy and embryo production.

Endocrine and molecular milieus of ovarian follicles are diversely affected by human chorionic gonadotropin and gonadotropin-releasing hormone in prepubertal and mature gilts

Different strategies are used to meet optimal reproductive performance or manage reproductive health. Although exogenous human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone (GnRH) agonists (A) are commonly used to trigger ovulation in estrous cycle synchronization, little is known about their effect on the ovarian follicle. Here, we explored whether hCG- and GnRH-A-induced native luteinizing hormone (LH) can affect the endocrine and molecular milieus of ovarian preovulatory follicles in pigs at different stages of sexual development. We collected ovaries 30 h after hCG/GnRH-A administration from altrenogest and pregnant mare serum gonadotropin (eCG)-primed prepubertal and sexually mature gilts. Several endocrine and molecular alternations were indicated, including broad hormonal trigger-induced changes in follicular fluid steroid hormones and prostaglandin levels. However, sexual maturity affected only estradiol levels. Trigger- and/or maturity-dependent changes in the abundance of hormone receptors (FSHR and LHCGR) and proteins associated with lipid metabolism and steroidogenesis (e.g., STAR, HSD3B1, and CYP11A1), prostaglandin synthesis (PTGS2 and PTGFS), extracellular matrix remodeling (MMP1 and TIMP1), protein folding (HSPs), molecular transport (TF), and cell function and survival (e.g., VIM) were observed. These data revealed different endocrine properties of exogenous and endogenous gonadotropins, with a potent progestational/androgenic role of hCG and estrogenic/pro-developmental function of LH.

Fixed-time artificial insemination protocols on brazilian locally adapted breed gilts on ovulatory response and embryo production

The aim of this study was to use estrus synchronization protocols to favor fixed-time artificial insemination and consequently fixed-time embryo collection, and increase embryo production using eCG, in gits. In a cross over design, nine Piau breed gilts were subjected to 18 days of oral progesterone; P4 group did not receive any further; GnRH group received 25µg of GnRH 104 hours after the final application of P4; and eCG+GnRH group received 1000IU of eCG 24 hours after the final P4 in addition to GnRH for subsequent embryo collection, that was performed six days after first AI, by laparotomy. Artificial insemination was performed after 12 and 24 hours of estrus in P4 group, and 128 and 144 hours in GnRH and eCG+GnRH groups. The number of CL (8.6±3.9; 8.3±2.1; 26.7±15.0) and anovulatory follicles (4.3±3.7; 3.9±3.9; 17.2±9.5) was higher in the eCG+GnRH gilts (P<0.05). However, the use of 1000 IU of eCG reduced (P<0.05) the number of total structures (5.2±3.6; 5.1±3.1; 1.7±2.7), viable embryos (5.0±3.5; 4.8±3.3; 0.4±0.7), freezable embryos (3.6±3.4; 3.3±3.8; 0.1±0.3) and recovery rate (63.7±38.9; 58.6±24.7; 5.38±9.5). P4 and GnRH protocols were effective in the production and recovery of embryos. However, the use of 1000 IU of eCG, 24 hours after P4, was not effective in promoting the production of embryos, although the animals had superovulated.

Ovarian morphometrical evaluation to assess reproductive activity suppression in heavy weight finishing gilts immunized against gonadotropin-releasing hormone

It is known that immunizing gilts against gonadotropin-releasing hormone (GnRH) is an efficient castration method that increases their growth performance. However, it is still unknown the ovarian histophysiology outcomes after this procedure. Therefore, the aim of this study was to investigate in detail, using morphological and morphometrical methods, changes in the ovarian structure that result in the suppression of ovarian activity, as well as to gain knowledge on the ovarian structure to assist in ovarian histopathological diagnoses. Seventy-two pre-pubertal finishing gilts were allocated to two experimental groups: immunized (IC; n = 36; gilts which received two injections of 2 mL of Vivax® - one at 15 and another at 19 weeks of age) and control (CT; n = 36, females which received two saline injections following the same protocol). All gilts were euthanized at 25 weeks of age and the ovaries of 5 gilts from each experimental group collected for biometrical and histomorphometrical analysis. IC gilts showed higher body weights, but smaller ovaries compared to CT females. In addition, the number of small follicles (≤ 2 mm) on the ovarian surface was higher, while no large follicles (> 6 mm) nor corpora lutea were found in the ovaries of IC gilts. Histomorphometrical analysis revealed that IC females showed higher numbers of quiescent and active primordial, primary, pre-antral and final stage atretic follicles. Moreover, follicle size, antrum diameter and area of the granulosa layer from mature follicles were smaller in IC gilts. Collectively, these results demonstrate that the efficacy of immunization against GnRH is related to the blockage of follicular recruitment and selection, thus suppressing reproductive activity in finishing gilts.

The effects of long- or short-term increased feed allowance prior to first service on litter size in gilts

Replacing stock is costly in any pig production. In addition, it takes time for young animals to reach the same level of productivity as more mature animals. Therefore, the aim of this study was to investigate the effects of long- or short-term increased feed allowance (covering the luteal and follicular phases) prior to service in the second estrus on first parity performance. In order to achieve this, altrenogest was used to synchronize the gilts cycle to allow a precise feeding strategy, and only gilts inseminated 0-10 d after altrenogest withdrawal were included in the study. Altrenogest was given at days 0-18 to control the luteal phase and, therefore, treatments covered different feeding strategies in either or both the luteal phase (days 0-18) and follicular phase (days 18-25). High feed allowance (H) was induced using 0.97 kg more feed per day compared to the low feed allowance (L) given 2.33 kg/d. Four feeding strategies, low-low (LL), high-high (HH), high-low (HL), and low-high (LH), were included. Once gilts had been inseminated, feed allowance was reduced to 2.23 kg/d to prevent the loss of embryos in early gestation. A tendency was observed between feeding strategy and backfat thickness before altrenogest treatment, showing that total born piglets were positively correlated to backfat in the LL and LH (no increased feed allowance or short-term increased feed allowance), treatments (P = 0.076), compared to when gilts had longer periods with high feed allowance (HH and HL). High feed allowance in the follicular phase (LH) tended to increase the number of total born piglets compared to the other groups (P = 0.069) when applied in the follicular phase of the second standing estrus after the gilts were given altrenogest. This would be equivalent to the last 5-7 d of a 21-d cycle in gilts. The three other feeding strategies, comprising either the luteal and follicular phases (HH) or the luteal phase (HL) or none (LL), did not increase litter size. The weight of the gilt when entering the insemination section also had an effect on total born piglets (P < 0.001) with an increase in litter size with increased weight of the sow, but no differences between treatments. In conclusion, the weight of the gilt had an influence on the total litter size and gilts with low backfat tended to respond more positively to a longer period with high feed allowance than fatter gilts.

Improving ovulation in gilts using anti-inhibin serum treatment combined with fixed-time artificial insemination

For successful batch farrowing, porcine oestrus and ovulation must be synchronized using fixed-time artificial insemination (FTAI). However, exogenous gonadotropins, which are currently used in FTAI, negatively affect gilt ovulation. Here, we aimed to improve sexually mature gilt superovulation efficiency using passive immunization against inhibin during FTAI. Altrenogest-treated gilts were challenged with 10 ml anti-inhibin serum (AIS group, n = 6), 1,000 IU pregnant mare serum gonadotropin (PMSG group, n = 6), or 10 ml goat serum (control group, n = 6). Gilts in the AIS and PMSG groups were inseminated according to the FTAI protocol, and gilts in the control group were inseminated during natural oestrus. When PMSG was replaced by AIS during FTAI of gilts, ovulation rate and embryos recovered were significantly greater in the AIS group as compared to the other two groups (p < .05). Especially the average number of 6-8-cell embryos in the AIS group was significantly higher than that in the PMSG group (p < .01). Moreover, the blastocyst number in the AIS group was significantly higher than that in the PMSG group and the control group (p < .05). But there was no significant difference in the blastocyst number between the PMSG group and the control group (p > .05). Besides, plasma levels of estradiol-β (E2) and progesterone (P4) were significantly greater in the AIS group as compared to the other two groups on Day 23 and D 27, respectively (p < .01). In summary, we devised an improved high-yield FTAI protocol for sexually mature gilts using AIS; this protocol had a greater superovulation efficiency than the FTAI using PMSG.

Altrenogest affects the development and endocrine milieu of ovarian follicles in prepubertal and mature gilts†

Altrenogest with gonadotropins is commonly used to synchronize the estrous cycle, but it can also lead to follicular cyst formation, especially in prepubertal gilts. Here, we aimed to investigate how maturity and altrenogest treatment affect the development, endocrine milieu, and molecular control of ovarian follicles. Crossbred prepubertal and mature gilts were challenged or not (control) with altrenogest, and ovaries were collected in the morning on the first day of behavioral estrus. In prepubertal gilts, altrenogest decreased the percentage of primordial and atretic small follicles, but increased large antral follicles when compared with controls. In mature gilts, altrenogest reduced the percentage of primary follicles and elevated the total number of antral follicles. Maturity affected the estradiol level in the follicular fluid of preovulatory follicles, luteinizing hormone (LH)-stimulated cyclic adenosine monophosphate (cAMP) generation, and LH receptor messenger RNA (mRNA) expression in granulosa. Moreover, cytochrome P45017A1 (CYP17A1) mRNA levels in the theca layer were affected and correlated with follicular androstendione and estradiol concentration. Altrenogest negatively affected follicular fluid progesterone concentration and decreased levels of prostaglandin (PG) E2 in prepubertal gilts and PGF2alpha metabolite in mature gilts. LH-stimulated cAMP release in granulosa cells of mature gilts as well as human chorionic gonadotropin- and forskolin-induced cAMP were also affected. In addition, altrenogest downregulated CYP17A1 mRNA in the prepubertal theca layer and PGF2alpha synthase expression in the granulosa and theca layer of mature gilts. To the best of our knowledge, this is the first study to report multiple effects of maturity and altrenogest on the endocrine milieu and molecular regulations governing ovarian follicle development in gilts.

Effects of intravaginal devices containing different dosages of medroxyprogesterone acetate for the control of the estrous cycle in gilts

This aim of this study was to investigate the effectiveness of intravaginal devices (IVDs), containing medroxyprogesterone acetate (MPA), for controlling the estrous cycle in pubertal gilts. Gilts were assigned to four treatments: Control (no IVD); IVD containing 100 (IVD100), 200 (IVD200) or 400 mg (IVD400) of MPA. The IVDs were inserted on day 12 of the estrous cycle and maintained intra-vaginally for 14 days. The percentage of gilts in estrus, interval between IVD removal and estrous onset, adjusted farrowing rate (AFR), total number of piglets born (TPB), follicle size and serum progesterone (P4) were recorded. None of the gilts expressed estrus during the IVD treatment period. All gilts of the control group expressed estrus (15/15; 100%) which was greater (P =  0.03) than all IVD-treated gilts (33/44; 75%); however, there were no treatment differences (P =  0.09). The interval between IVD removal and estrous onset was shorter for IVD100 (3.8 ± 0.6 d) compared to IVD400 (5.3 ± 0.6 d; P = 0.05). The IVD400-treated gilts had smaller follicles than the IVD100-treated gilts (P =  0.05). The P4 concentrations were similar among treated groups (P =  0.99). The AFR did not differ among treatment groups (P = 0.37); however, the control group had a greater TPB than the other treatment groups (P =  0.04). The gilts treated with IVDs had longer interval to estrous expression. The most effective dosage was 400 mg of MPA, considering both the minimal follicular growth during the IVD treatment period and the lesser numbers of persistent follicles.

Single injection of eCG/hCG leads to successful estrous synchronization in the collared peccary (Pecari tajacu Linnaeus, 1758)

The establishment of protocols for the control of the ovarian function of collared peccaries is recommended for the development of assisted reproductive techniques. The goals were to (1) compare a gonadotropin combination with prostaglandin analogue to synchronize timing of onset of estrus among animals, and (2) elucidate the effects of the most desirable protocol for performing an artificial insemination study and macroscopic evaluation of the ovaries. Three of five females treated with a double administration of 120 μg prostaglandin (cloprostenol) at a 9-day interval expressed symptoms of estrus 9 days after the second injection. One female presented estrus after 6 days, whereas other did not respond to the treatment. All females (5/5) treated with a single dose containing 400 IU eCG and 200 IU hCG manifested estrus 6 days after the hormone injection. In a second experiment, ten females that were estrous synchronized using eCG/hCG, were artificially inseminated with fresh semen and monitored for pregnancy every 30 days. Although there was no detection of fetuses by ultrasonic examination, seven females (7/10) had greater than basal progesterone values for 60 days after the treatments were imposed. Ovaries from two females treated with eCG/hCG were collected 6 days post-injection. There was confirmation of an ovarian stimulation as a result of the presence of 88 and 25 antral follicles, as well as three and eight hemorrhagic structures in ovaries of each female, respectively. It, therefore, is proposed that eCG/hCG can be used as an effective treatment for estrous synchronization in collared peccaries.

Seasonal infertility in gilts and sows: Aetiology, clinical implications and treatments

In gilts and sows, the summer-autumn period often is characterized by reduced fertility. Heat stress and long photoperiods during the warm season can cause a reduction in feed intake and an imbalance of the hypothalamic-hypophysial-ovarian axis. The increased variability in the interval between oestrus onset and ovulation results in an increased number of poorly timed inseminations. The altered endocrine activity compromises follicular and corpora luteal development, reduces oocyte quality and increases embryo mortality. This paper reviews current knowledge on the metabolic and endocrine mechanisms associated with seasonal infertility in gilts and sows and describes some pharmacological approaches that can be utilized to counter this infertility.