Luteinizing hormone release after administration of the gonadotropin-releasing hormone agonist Fertilan (goserelin) for synchronization of ovulation in pigs

Application of Exogenous GnRH in Food Animal Production

Over several decades, exogenous GnRH and agonists have been employed for controlling reproductive cascades in animals, and treating some reproductive morbidities. The administration of GnRH is used in animals to counter ovarian dysfunction, induce ovulation, and to increase conception and pregnancy rates. GnRH and its agonists are used in the treatment of cystic ovarian degeneration and repeat breeder syndrome. The development of protocols for GnRH administration by intramuscular injection, intramuscular or subcutaneous implants, and intravaginal deposition has empowered their clinical use worldwide. Currently, exogenous GnRH products are a central part of several pre- and post-breeding programs for the enhancement of fertility, including the control of estrous cycles and timing of ovulation, development of fixed-time artificial insemination protocols, improved embryo survival, and the treatment of reproductive morbidity. The aim of the present review is to summarize the application of exogenous GnRH agonists in food animal production.

GnRH agonists: Updating fixed-time artificial insemination protocols in sows

Protocols for fixed-time artificial insemination (FTAI) in swine reproduction can help increase genetic improvement and production efficiency. Different gonadotropin-releasing hormone (GnRH) agonists have been developed to gain better control of follicular development, timing, and ovulation quality; therefore, they have been extensively used in FTAI protocols. This literature review resumes the most important characteristics of the physiology of follicular development and ovulation in sows, followed by a discussion about the hormonal alternatives available to induce ovulation (human chorionic gonadotropin, hCG; porcine luteinizing hormone, LH and GnRH agonists). Also, ovulation induction failures with GnRH agonists are described. Finally, current FTAI protocols with GnRH agonists are resumed and discussed. FTAI with GnRH agonists has proven to be an efficient, successful reproductive protocol that can be implemented in pig farms due to better knowledge of an endocrine system that regulates follicular development and ovulation and increased availability of several GnRH agonists that allow more efficient reproductive swine programs.

Spray congealed solid lipid microparticles as a sustained release delivery system for Gonadorelin [6-D-Phe]: Production, optimization and in vitro release behavior

Sustained release lipid microparticles for a potential veterinary application were produced by the means of spray congealing using saturated triglycerides with respective surfactants. The spray congealing process was optimized using unloaded and loaded microparticles, revealing the highest impact of the spray flow on material loss. Yield could be optimized by increasing the spray flow as well as a reduction of the melt temperature from 90 to 75 °C. For the delivery system developed in this study, a release of around 15 days was targeted. The release profile was in first hand determined with the use of model substances (aspartame and tryptophan), before incorporating the decapeptide Gonadorelin [6-D-Phe]. Release could be controlled between 2 and 28 d, which was dependent on stability of microparticles upon incubation, type and concentration of emulsifier, as well as the used triglyceride. Differential scanning calorimetry and X-ray powder diffraction confirmed the crystallization behavior of C14 and C16-triglycerides in combination with various emulsifiers in different modification without impact on release.

Comparison of Single, Fixed-Time Artificial Insemination in Gilts Using Two Different Protocols to Synchronize Ovulation

Simple Summary

It is necessary to have a consistent supply of service-ready gilts available to incorporate into each batch of breeding sows. Techniques to manipulate the timing of estrus and possibly the timing of ovulation in gilts are helpful in order to achieve this goal. This study investigated two different techniques for inducing ovulation to allow fixed-time artificial insemination (FTAI) protocols in gilts and compared results with gilts bred when observed in standing heat following cessation of daily altrenogest treatment. Pubertal gilts (n = 180) were assigned to one of three treatment groups. Group 1 gilts (LUT, n = 62) were induced to ovulate utilizing intramuscular injections of equine chorionic gonadotropin followed by porcine luteinizing hormone, and bred using a single FTAI. Group 2 gilts (TRI, n = 61) were induced to ovulate by intravaginal deposition of triptorelin acetate and were bred by a single FTAI. Group 3 gilts (CON, n = 57) were observed for estrus and bred twice (24 h apart) using artificial insemination (AI). LUT and TRI gilts completed farrowing in a smaller window of time compared to CON gilts; however, they also tended to have poorer reproductive performance. LUT and TRI piglets were 80 g and 64 g, respectively, heavier at weaning than CON piglets. Results indicate that FTAI might be useful as a means of minimizing the range in lactation length in a farrowing batch. However, modifications of the protocols may be required to ensure optimum farrowing rates and litter size.

Abstract

In order to efficiently have a consistent supply of service-ready gilts available to incorporate into each batch of breeding sows, it is necessary to manipulate the timing of estrus and possibly the timing of ovulation of gilts. Estrus can be synchronized by the withdrawal of altrenogest after at least 14 days of treatment. It is possible that protocols developed to induce ovulation, and therefore allow fixed-time artificial insemination (FTAI), can improve the predictability of gilt breeding. This study investigated the effect of two FTAI protocols in gilts on reproductive performance and timing of farrowing and piglet weaning weight compared to gilts bred based on signs of estrus after cessation of altrenogest. Puberty was induced in gilts, followed by treatment with altrenogest. Following altrenogest withdrawal, 180 gilts were assigned to one of three treatment groups. Group 1 gilts (LUT, n = 62) were treated with 600 IU equine chorionic gonadotropin 24 h after altrenogest withdrawal and 5 mg porcine luteinizing hormone (pLH) 80 h later, followed by a single FTAI 36 h after pLH. Group 2 gilts (TRI, n= 61) received 2 mL of a gonadotropin-releasing hormone agonist, triptorelin acetate, intravaginally 6 d after altrenogest withdrawal and were bred by a single FTAI 24 h later. Group 3 gilts (CON, n = 57) were observed for estrus and bred twice by AI, 24 h apart. LUT and TRI gilts farrowed closer together (2.4 ± 1.6 and 2.9 ± 1.2 d(days), respectively) compared to CON gilts (4.5 ± 3.3 d). Piglets in LUT were 80 g (p < 0.001) heavier and piglets in TRI were 64 g (p < 0.05) heavier at weaning than CON piglets, when controlling for birth weight. Results indicate that FTAI might be useful as a means of minimizing the time from the first to the last gilt farrowing in a breeding batch of gilts. However, modifications of the protocols may be required to ensure optimum farrowing rates and litter size.

Invited review: reproductive physiology in commercial and premium pig breeds – history of 30-year-long cooperation

Abstract. Cooperation of the Hungarian Research Institute for Animal Breeding and Nutrition (ATK) with the German Leibniz Institute for Farm Animal Biology (FBN) goes back many decades. In 1988 the two departments of reproductive biology began a joint project concerning on ovulation investigation in Landrace pigs. This joint project laid the foundation for further joint projects and has existed for almost 30 years. Over the years, the main focus has always been on the events of the female reproductive tract in pigs, i.e., follicular growth, ovulation, transport of gametes in the oviduct, fertilization and early embryonic development. Nearly all studies were done under in vivo circumstances and using different clinical and endocrinological methods, enabling us to obtain more profound knowledge of the dynamics of reproductive processes. Even results considered to be basic scientific achievements were available for utilization in the daily practice of porcine reproductive management. Since the end of the 1990s, the common projects have been gradually shifted to the physiology of the Hungarian indigenous pig breed Mangalica. Research partners were convinced that modern utilization of indigenous pig breeds would open new doors for premium pork production. In addition to the Mangalica breed, this principal was broadened to non-European fatty-type native pig breeds as well and resulted in long-term, intercontinental scientific cooperation.

Advances in Breeding Management and Use of Ovulation Induction for Fixed-time AI

The objective of the breeding herd is the predictable and consistent production of high quality pigs. To achieve this objective, an appropriate number of females need to be mated in each breeding week and they should maintain their pregnancy and deliver large litters. Many factors can impact achievement of optimal sow productivity, particularly breeding management. Most matings will involve artificial insemination (AI), and successful AI requires deposition into the cervix (or beyond) of sufficient viable high quality sperm at an appropriate time relative to ovulation. This is facilitated by improved knowledge of the sow's ovarian function prior to and during her oestrous period. Realization of the importance of establishing an adequate sperm reservoir in the oviduct at an appropriate time relative to ovulation has led to advances in the management of AI. The future of AI will likely involve insemination of single doses of high genetic merit semen, potentially having a reduced sperm concentration which is made possible by knowledge of the effect of site of sperm deposition on sow fertility. In particular, knowledge of when a sow is likely to ovulate during a natural or induced oestrous period will prove invaluable in the maintenance of herd productivity. This review will examine options for breeding management, including the control of oestrus and ovulation, on sow herd reproductive performance.

Recent advancements in the hormonal stimulation of ovulation in swine

Induction of ovulation for controlled breeding is available for use around the world, and conditions for practical application appear promising. Many of the hormones available, such as human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH) and its analogs, as well as porcine luteinizing hormone (pLH), have been shown to be effective for advancing or synchronizing ovulation in gilts and weaned sows. Each of the hormones has unique attributes with respect to the physiology of its actions, how it is administered, its efficacy, and approval for use. The timing for induction of ovulation during the follicle phase is critical as follicle maturity changes over time, and the success of the response is determined by the stage of follicle development. Female fertility is also a primary factor affecting the success of ovulation induction and fixed time insemination protocols. Approximately 80%-90% of female pigs will develop mature follicles following weaning in sows and synchronization of estrus in gilts. However, those gilts and sows with follicles that are less developed and mature, or those that develop with abnormalities, will not respond to an ovulatory surge of LH. To address this problem, some protocols induce follicle development in all females, which can improve the overall reliability of the ovulation response. Control of ovulation is practical for use with fixed time artificial insemination and should prove highly advantageous for low-dose and single-service artificial insemination and for use with frozen-thawed and sex-sorted sperm.

Effects of altering the dose and timing of triptorelin when given as an intravaginal gel for advancing and synchronizing ovulation in weaned sows

Previous studies have shown that triptorelin gel (TG) given intravaginally in gel form is effective for advancing the time of ovulation in weaned sows. Three experiments were performed to determine the effects of altering the dose and timing of administration of intravaginal TG for advancing and synchronizing ovulation in weaned sows. In all experiments, estrus was detected twice or three times daily and ultrasound was performed to determine ovulation at 8-hour intervals. In experiment 1, sows (n = 131) received intravaginal gel containing 0 (Placebo), 25, 100, or 200 μg of TG at 96 hours after weaning and sows were inseminated on each day of standing estrus. Wean-to-estrus interval and duration of estrus were correlated (P < 0.0001) with estrus duration longer in TG (P < 0.05) compared with Placebo. More sows ovulated (P < 0.001) by 48 hours after treatment with 200 (81%), 100 (64%), and 25 μg (63%) of TG compared with Placebo (42%). The farrowing rate and total pigs born did not differ (P > 0.10). In experiment 2, sows (n = 126) received 200 μg of TG at 72, 84, or 96 hours after weaning or were untreated (Control-96). Sows receiving TG were inseminated once 24 to 28 hours after treatment. Control-96 sows were inseminated on each day of standing estrus. Wean-to-estrus interval was not affected by treatment, but wean-to-ovulation interval was reduced (P < 0.05) by TG-72 and TG-84 compared with TG-96 and Control-96. More sows ovulated 40 hours after treatment (P < 0.001) with TG-72 (56.5%) and TG-84 (32.2%) compared with TG-96 and Control-96 (13%) and for all TG treatments 48 hours after treatment (64%) compared with Control-96 (34%, P < 0.05). The farrowing rate was lower (P < 0.05) for sows assigned to TG-72 and TG-84 compared with TG-96 and Control-96, whereas the number of liveborn pigs did not differ (P > 0.10). In experiment 3, sows (n = 113) were assigned to receive no treatment (Control), intravaginal gel alone (Placebo), or 200 μg of TG given intravaginally (OvuGel) at 96 hours after weaning. Wean-to-estrus interval did not differ, but the duration of estrus tended (P < 0.10) to be reduced with OvuGel compared with the other treatments. More sows ovulated (P < 0.001) by 48 hours after OvuGel treatment (79.1%) compared with Control (46.4%) and Placebo (37.9%) and by 56 hours (P < 0.05). The farrowing rate and the number of liveborn pigs did not differ among treatments. The results of these studies indicate that 200 μg of TG given intravaginally at 96 hours after weaning (OvuGel) synchronizes ovulation and results in fertility similar to Controls.

An ultrasonographic study of ovarian antral follicular dynamics in prepubertal gilts during the expected activation of the hypothalamo-pituitary-ovarian axis

Daily transrectal ultrasonography was carried out in eight 4-5-month-old Polish Large White×Polish Landrace gilts for 42 days to monitor the growth of individual ovarian antral follicles≥2 mm in diameter. In total, 52.4±16.2 and 123.0±6.7 follicles per gilt (mean±SD) that grew to ≥4 mm were identified during the first and second 21-day study periods, respectively (P<0.01). Four follicular waves (defined as the synchronous growth of a group of follicles from 2-3 mm to ≥4 mm) emerged during the first period, and five waves emerged during the second period. The maximum diameters attained by the largest follicles of waves were 5.7±0.6 and 7.0±0.5 mm (first and second periods, respectively; P<0.01). The present results provide direct evidence for the rhythmic, wave-like pattern of antral follicle recruitment in prepubertal gilts. The number of follicles and maximum diameter they attain increase significantly during the expected activation of the hypothalamo-pituitary-ovarian axis in prepubescent gilts.

Induction and synchronization of ovulations of nulliparous and multiparous sows with an injection of gonadotropin-releasing hormone agonist (Receptal)

The objective of this study was to determine if administration of a set dose (10 microg) of a gonadotropin-releasing hormone agonist, buserelin (Receptal; Rc), at set times after altrenogest (Regumate; RU) treatment or after weaning was able to induce and synchronize ovulation in female swine (gilts and sows). The pubertal (n=187) gilts were allocated to four groups, all synchronized with RU. Group 1 (RU) was inseminated twice at detected estrus, Group 2 (RU+Rc120) and Group 4 (RU+Rc104) received 10 microg Rc at 120 or 104 h after the end of RU treatment, respectively, and Group 3 (RU+eCG+Rc104) was treated with 800 IU equine chorionic gonadotropin (eCG) at 24h and Rc 104 h after the end of RU treatment, respectively. Gilts were inseminated twice at predetermined times, namely 144 and 168 h (Group 2), 128 and 144 h (Group 3), and 144 and 152 h (Group 4) after the end of RU treatment, respectively. Pregnant gilts were slaughtered at 30 d. Administration of Rc 104 h after the end of RU feeding synchronized ovulation over a 24-h time window in 97.9% and 100% of the gilts of Groups 3 and 4, respectively, whereas Rc administration at 120 h (Group 2) only successfully synchronized 88.9% of the gilts over 24h. Ovulation rates of gilts of Groups 2 and 4 were similar to that of the control group. Pregnancy rates were numerically higher in Groups 2 and 3 (92% and 96%, respectively) compared with those of Groups 1 and 4 (84% and 81%, respectively). Combination of eCG with Rc administration at 104 h (Group 3) increased ovulation rate (+4 CL) but decreased embryo survival to 62% at Day 30. The weaned sow experiment involved 61 sows of a range of parities (2.7+/-0.9), allocated to two control groups (Control 104 group and Control 94 group) and two treated groups (Rc104 group and Rc94 group), which received 10 microg Rc at 104 and 94 h after weaning, respectively. The females were inseminated at detected estrus. All pregnant sows farrowed. After treatment with Rc 94 h after weaning, 100% of sows ovulated over a 24-h time window versus only 68.7% of controls. Farrowing rate and litter size of the sows treated with Rc at that time were unaffected compared with that of control sows. In contrast, Rc administration at 104 h after weaning may have been too late; only 66.7% of the treated sows ovulated during a 24-h period. This proportion was numerically lower but not significantly different than that for control sows. Farrowing rate and litter size of treated sows were not significantly different than that of controls. Administration of Rc at the dose and times selected in this study tightened synchrony of ovulation in gilts and in sows after weaning. It remains to be established if such a synchrony is suitable to obtain good fertility after a single artificial insemination at a predetermined time.

Physiological mechanisms of ovarian follicular growth in pigs--a review

Follicular growth after antrum formation is determined by follicle-stimulating hormone (FSH). Only two ways are possible for recruited follicles, continuing development or atresia. In gilts, intensive ovarian follicular growth begins between 60 and 100 days of age, and fluctuations of the ovarian morphological status last about 20 days; however, at that time there are no really large follicles. Final follicular development is under luteinising hormone (LH) control; this is why the attainment of puberty is related to an increase in serum oestradiol to a level that causes a preovulatory surge of this gonadotropin. The pool of follicles at the beginning of the oestrous cycle is about 30-40, most of which are small (< 3 mm) and growing. Then, the pool of follicles increases to about 80 in the mid-luteal phase but about 50 of them are small and 30 are medium sized (3-6.9 mm). Some of these follicles are in the growing phase, but some are atretic. Between days 7 and 15 of the oestrous cycle the percentage of atretic follicles fluctuates between 12 and 73%. At that time there are no large (> 7 mm) follicles because of the suppressing effect of progesterone. The number of small follicles declines after luteolysis. From the pool of medium follicles, large follicles are selected under the influence of LH, but about 70% of the medium-sized follicles become atretic. Because of the long-lasting selection process there is a significant heterogeneity in the diameter of large follicles in oestrus. However, the number of follicles correlates with the number of corpora lutea after ovulation. Individual follicular development and the relationship between follicles are still poorly known. The use of ultrasonography may give a closer insight into these phenomena.

Study of enteral versus parenteral application of the gonadotropin releasing hormone agonist Gonadorelin[6-D-Phe] (D-Phe6-LHRH) on LH secretion in Goettinger miniature pigs

With respect to the assessment of residue situation and as a part of preclinical trials to determine the biological activities of potential gonadotropin releasing hormone (GnRH) residues in porcine organisms the GnRH agonist Gonadorelin[6-D-Phe] (D-Phe(6)-LHRH) was administered either enterally or intramuscularly (i.m.) to female Goettinger miniature pigs in order to evaluate the GnRH-induced luteinizing hormone (LH) surge. Gilts received an (i) enteral application of 10 mg D-Phe(6)-LHRH via a probang (enteral group, n=7), (ii) i.m. injection of 0.1 mg D-Phe(6)-LHRH (parenteral group, n=5), or (iii) saline injection (control group, n=4). The GnRH and saline applications were repeated every second day with up to seven repetitions. Blood samples were collected via previously fitted jugular catheters immediately before injections, over an 8 h period in 1 h intervals beginning 2 h after injections, and at 24, 26, 28 and 30 h after applications. Enteral application of D-Phe(6)-LHRH induced an LH surge in 23 of 30 treatments. All gilts in the parenteral group exhibited LH release after each D-Phe(6)-LHRH application (P<0.05), whereas no LH surges were observed after saline injection in the control group. A significant (P<0.05) LH rise to mean maximum LH concentrations of 3.25 +/- 0.43 and 3.05 +/- 0.26 ng/ml occurred in both the enteral and parenteral groups, but there was no difference in the time interval after GnRH (2.6 +/- 0.3 vs. 2.3 +/- 0.3 h) and the mean duration of LH peak (6.5 +/- 0.4 and 6.8 +/- 0.3 h) between the treatment groups. In conclusion, (i) enteral application of 10 mg D-Phe(6)-LHRH induced LH release in a physiological range from the pituitary of female minipigs, and (ii) neither an accumulative effect nor a cumulative LH response were found after repeated GnRH application. Furthermore, (iii) in regard to consumer protection and gonadotropin secretion, D-Phe(6)-LHRH residues can be excluded from having long-term effects.