Synchronization of ovulation in yaks (Poephagus grunniens L.) using PGF2α and GnRH

Serum Metabolomic Analysis of Synchronous Estrus in Yaks Based on UPLC-Q-TOF MS Technology

The yak is a unique species of livestock found in the Qinghai-Tibet Plateau and its surrounding areas. Due to factors such as late sexual maturity and a low rate of estrus, its reproductive efficiency is relatively low. The process of estrus synchronization in yaks plays a crucial role in enhancing their reproductive success and ensuring the continuation of their species. In order to clarify the characteristics of the serum metabolites of yak estrus synchronization, the yaks with inactive ovaries were compared with the estrus synchronization yaks. In this study, yaks were divided into the inactive ovaries group (IO), gonarelin-induced yak estrus group (GnRH), and chloprostenol sodium-induced yak estrus group (PGF). After the completion of the estrus synchronization treatment, blood samples were collected from the jugular veins of the non-estrus yaks in the control group and the yaks with obvious estrus characteristics in the GnRH and PGF groups. Metabolites were detected by ultra-high performance liquid chromatography-mass spectrometry, and differential metabolites were screened by multivariate statistical analysis. The results showed that a total of 70 significant differential metabolites were screened and identified in the GnRH vs. IO group, and 77 significant differential metabolites were screened and identified in the PGF vs. IO group. Compared with non-estrus yaks, 36 common significant differential metabolites were screened out after the induction of yak estrus by gonarelin (GnRH) and cloprostenol sodium (PGF), which were significantly enriched in signaling pathways such as the beta oxidation of very long chain fatty acids, bile acid biosynthesis, oxidation of branched chain fatty acids, steroidogenesis, steroid biosynthesis, and arginine and proline metabolism. This study analyzed the effects of gonadotropin releasing hormone (GnRH) and prostaglandin F (PGF) on the reproductive performance of yaks treated with estrus synchronization, which provides a theoretical basis for the optimization and application of yak estrus synchronization technology and promotes the healthy development of the yak industry.

Dynamic changes in gene expression during follicle development and the efficacy of four timed AI protocols in non-suckling female yaks (Bos grunniens)

The objectives of the study were to investigate changes in the mRNA expression levels of five genes during antral follicle development and to assess the efficacy of four timed-artificial insemination (TAI) protocols in female yaks (Bos grunniens). RT-qPCR analysis revealed that expression levels were greater for follicle-stimulating hormone receptor and bone morphogenic protein 15 in the small follicle, luteinizing hormone receptor, and kit ligand in the large follicle, and growth differentiation factor 9 in the medium follicle (p < 0.05). Non-suckling yaks were treated as a 7-d CIDR, and PGF_2α + eCG at CIDR withdrawal and TAI with frozen yak semen at 56-58 h after PGF_2α (PPe-7d); either a 7-d CIDR (PPG-7d) or a 5-d CIDR (PPG-5d), and PGF_2α at CIDR withdrawal and TAI + GnRH at 70-72 h after PGF_2α; and GnRH treatment on Day 0, followed by PGF_2α on Day 7 and TAI + GnRH on Day 9 (GPG-7d). The results showed that the pregnancy rate (P/AI) was greater in PPG-5d than in GPG-7d (p < 0.05), but the P/AI was not different among the other TAI protocols. In conclusion, the expression levels of these genes in follicles are dynamically changed during antral follicle development in yaks. The PPG-5d protocol achieved a greater P/AI.

Reproduction in female wild cattle: Influence of seasonality on ARTs

Wild cattle species, often considered less alluring than certain conservation-dependent species, have not attracted the same level of interest as the charismatic megafauna from the general public, private or corporate donors, and other funding agencies. Currently, most wild cattle populations are vulnerable or threatened with extinction. The implementation of reproductive technologies to maintain genetically healthy cattle populations in situ and ex situ has been considered for more than 30 years. Protocols developed for domestic cattle breeds have been used with some success in various wild cattle species. However, inherent differences in the natural life history of these species makes extrapolation of domestic cattle protocols difficult, and in some cases, minimally effective. Reproductive seasonality, driven by either photoperiod or nutritional resource availability, has significant influence on the success of assisted reproductive technologies (ARTs). This review focuses on the physiological processes that differ in breeding (ovulatory) and non-breeding (anovulatory) seasons in female cattle, and the potential methods used to overcome these challenges. Techniques to be discussed within the context of seasonality include: estrus synchronization and ovulation induction, ovarian superstimulation, artificial insemination (AI), multiple ovulation embryo transfer (MOET), and ovum pick-up (OPU) with in vitro fertilization (IVF) and embryo transfer (ET).

Transcriptome analysis revealed key signaling networks regulating ovarian activities in the domestic yak

Domestic yaks are the most important livestock species on the Qinghai-Tibetan Plateau. Adult female yaks normally breed in warm season and enter anestrous in cold season. Currently, how the ovarian activity is regulated at the molecular level remains to be determined. This study was conducted to investigate follicular development and gene expression patterns of yak ovarian tissues in the warm and cold seasons. Dynamics of follicular development was evaluated based on histological analyses and global gene expression was examined by using RNA-sequencing (RNA-seq) technology. Firstly, we found that follicle development of yak cows in cold season was different from that in warm season. Interestingly, ovaries collected from yaks in cold season contained a significant higher number of antral follicles and some of these follicles showed signs of polycystic structure, indicating abnormal granulosa cell function. RNA-seq analyses of ovarian tissues from non-pregnant adult yaks in cold and warm season revealed that a list of 320 transcripts were differentially expressed, specifically, 79 were up-regulated and 241 were down-regulated in the ovaries from yaks during the cold season. Further analysis demonstrated that transcripts associated with estrogen secretion and metabolism signaling pathway were altered, including FST, CYP1A1, PIK3R1 and PIK3R2. This study showed histological features of follicle development and revealed candidate genes that may have important roles in regulating ovarian activities in the yak seasonal reproduction.

Ovulatory and fertility response using modified Heatsynch and Ovsynch protocols in the anovular Murrah buffalo (Bubalus bubalis)

We studied the effect of modified Heatsynch and Ovsynch protocols on the ovulatory response (OR), estrus induction rate (EIR) and conception rate (CR) in the anovular postpartum Murrah buffalo (n = 35). In the modified Heatsynch protocol (Group I; n = 12), buffaloes were given two GnRH at 2 h interval on treatment day 0, PGF (PGF2α) on day 7 and estradiol (E₂) 1 mg on day 8. Two FTAI were done at 20 h intervals after E₂ administration. In the modified Ovsynch protocol (Group II; n = 15), GnRH was given on day 0, 7 and 16 with a PGF on day 14. Two FTAI were done; one at last GnRH and the other 20 h later. Group III served as untreated negative control (n = 8). During the treatment, ovarian changes were monitored by transrectal ultrasonography and plasma progesterone (P₄) and E₂. Administration of two GnRH at 2 h interval neither increased the OR nor strengthened the subsequent P₄ priming. Interestingly, in group I, none of the buffalo ovulated to E₂ though the EIR was 100% indicating the occurrence of behavioral, but not ovulatory estrus. Administration of GnRH 7 day prior to the commencement of Ovsynch protocol (Group II) did not improve the CR (21.4%), though the OR was 71.4%. No significant difference was found in the diameter of largest follicle between the ovulated and non-ovulated buffalo in response to GnRH suggesting that follicle of ≥9.5 mm is necessary but not sufficient to induce ovulation in the anovular buffalo. In both the protocols, the plasma P₄ was higher on day 7 in those buffaloes that ovulated to GnRH. Buffaloes treated with modified Ovsynch regimens were 5.27 times more likely to become pregnant than modified Heatsynch protocol. It is concluded that modified Ovsynch protocol is superior to modified Heatsynch protocol in terms of OR and CR.

Comparative Proteomic Analysis of Yak Follicular Fluid during Estrus

The breeding of yaks is highly seasonal, there are many crucial proteins involved in the reproduction control program, especially in follicular development. In order to isolate differential proteins between mature and immature follicular fluid (FF) of yak, the FF from yak follicles with different sizes were sampled respectively, and two-dimensional gel electrophoresis (2-DE) of the proteins was carried out. After silver staining, the Image Master 2D platinum software was used for protein analysis and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) was performed for differential protein identification. The expression level of transferrin and enolase superfamily member 1 (ENOSF1) was determined by Western blotting for verification analysis. The results showed that 2-DE obtained an electrophoresis map of proteins from mature and immature yak FF with high resolution and repeatability. A comparison of protein profiles identified 12 differently expressed proteins, out of which 10 of them were upregulated while 2 were downregulated. Western blotting showed that the expression of transferrin and ENOSF1 was enhanced with follicular development. Both the obtained protein profiles and the differently expressed proteins identified in this study provided experimental data related to follicular development during yak breeding seasons. This study also laid the foundation for understanding the microenvironment during oocyte development.

Application of sensitive enzymeimmunoassay for determination of testosterone in blood plasma of yaks (Poephagus grunniens L.)

As an alternative to radioimmunoassays, a simple, highly sensitive and quick enzymeimmunoassay (EIA) for determination of testosterone in blood plasma of yaks on microtitreplates using second antibody coating technique and testosterone-horseradish peroxidase as a label has been developed for the first time. The wells of the microtitreplate were coated with affinity-purified goat immunoglobulin (antirabbit IgG) that binds the hormone specific antibody. The EIA was carried out directly in 20 mICROl of plasma after 1:10 dilution with assay buffer. The testosterone standard curve ranged from 0.2 to 200 pg/well. The sensitivity of the assay was 0.20 pg/well. Testosterone standard curve in buffer showed parallelism with serially diluted yak plasma containing high endogenous testosterone. Intra- and inter-assay coefficients of variation (CV) determined using pooled plasma was found 5.24 and 8.54%, respectively. Recovery of known concentrations of added testosterone in charcoal stripped plasma was linear (r=0.98). For biological validation of testosterone enzymeimmunoassay, the blood samples were collected from yak cows at -2h before and thereafter at 2h interval until 24h. after gonadotropin releasing hormone (GnRH) administration. There was a rapid increase (p<0.01) of luteinizing hormone (LH) and testosterone 2 and 6h after GnRH administration. Plasma testosterone concentration in normal adult yak bulls was found to be 0.52+/-0.09 ng/ml. In conclusion, the EIA developed in this study is simple, highly sensitive, valid and sufficiently reliable method for estimation of testosterone directly in yak plasma.

Efficacy of Heatsynch protocol for induction of estrus, synchronization of ovulation and timed artificial insemination in yaks (Poephagus grunniens L.)

The objective of this study was to test the efficacy of induction of estrus, synchronization of ovulation and timed artificial insemination in anestrous yaks using the Heatsynch protocol. In Experiment 1, 10 anestrous yaks were administered an analogue of gonadotropin releasing hormone (GnRH) followed by prostaglandin (PG)F2alpha 7 days later and then estradiol cyponate (ECP) 24 h after that. Ovulation was detected by rectal palpation at 2h intervals beginning at the initial signs of estrus. Blood samples were collected at 2h intervals beginning at the time of ECP injection up to 2h after the occurrence of ovulation for the determination of LH and progesterone. All the animals responded to the Heatsynch protocol with expression of estrus and synchronization of ovulation. The mean time interval from the ECP injection to ovulation was 59.4+/-2.62 h (range 50-72 h). The interval from the LH peak to ovulation was 30.2+/-2.3 h. The high degree of synchrony in ovulation could be attributed to the synchrony in the timing of LH peaks. In Experiment 2, 10 anestrous yaks were treated with the Heatsynch protocol (as in Experiment 1) and TAI was performed at 48 and 60 h after the ECP treatment. Concurrently, 16 cycling yaks were inseminated approximately 12 h after detection of spontaneous estrus. Pregnancy rates were similar in both groups, 40% for TAI and 43.75% for yaks inseminated following spontaneous estrus (p>0.05). From this study, two conclusions can be drawn. First, the Heatsynch protocol can be successfully used to induce and synchronize estrus in anestrous yaks and, second, ovulation following the Heatsynch protocol is synchronized adequately to permit the use of fixed time AI in this species.

Calves Born from Anestrus Yaks (Poephagus grunniens L.) Subjected to Ovsynch and Superovulation Treatment

An attempt was made to induce estrus and ovulation in eight anestrus yaks by use of the Ovsynch protocol. Six out of eight yaks were successfully induced into estrus, and ovulation occurred in all the responding yaks 1-2 days after the second GnRH administration. Out of the six animals that responded to the treatment, two mated naturally with yak bulls, and calves were obtained from them. The other four animals were further administered a superovulatory regimen of Folltropin (FSH-P). Following Folltropin and Ilerin (a PGF(2alpha) analog) treatment, the animals were subjected to natural insemination. Only one animal in which natural mating occurred was flushed non-surgically for embryo recovery 7 days post-insemination. Thereafter, all the donor animals were administered with Ilerin. After 48-72 h, they came into heat and mated naturally with yak bulls, and calves were obtained from them after expiration of the normal gestation period. Following superovulation, the average numbers of palpable corpora lutea in the right and left ovaries were 2.25+/-0.6 and 1.75 +/-0.3, respectively. Three embryos were recovered by non-surgical flushing from a single animal. One embryo was transferred to a recipient yak, who produced one female calf after 258 days. This is the first report of production of a yak calf through embryo transfer-technology.

Induction of estrus in suckled female yaks (Bos grunniens) and synchronization of ovulation in the non-sucklers for timed artificial insemination using progesterone treatments and Co-Synch regimens

The objectives of the present study were to evaluate the induction of estrus and fertility in yak cows treated with Co-Synch regimens or progesterone (P(4)). In Experiment 1, postpartum suckled yaks were assigned to three treatments: (1) A (n=28), insertion of an intravaginal device containing P(4) (CIDR) on Day 0, PGF(2alpha) (i.m.) on Day 6 and PMSG (i.m.) at the time of CIDR removal on Day 7 (P(4)-PGF(2alpha)-PMSG); (2) B (n=21), PGF(2alpha) (i.m.) on Day 6 and PMSG on Day 7; (3) C (n=26), control group. Seven yak bulls were grazed with the cows for natural breeding. Rate of estrus within 96h of the end of treatment was greater (P<0.05) in A (100.0%) than in B (28.6%) or C (0.0%). First service conception rate (CR) determined by serum P(4) on Day 21 after breeding was greater (P<0.05) in A (78.6%) than in B (22.2%). Also, pregnancy rate (PR) during the breeding season was greater (P<0.05) in A (82.1%) than in B (19.0%) and C (7.7%). In Experiment 2, non-suckled yaks that calved in previous years but not in the current year were assigned to three treatments: (1) A (n=31), GnRH (i.m.) on Day 0, followed by PGF(2alpha) on Day 7 and timed artificial insemination (TAI) concurrently with GnRH treatment on Day 9 (Co-Synch regimen); (2) B (n=50), a CIDR device for 7 days plus PGF(2alpha) and PMSG at the time of CIDR withdrawal on Day 7 and TAI on Day 9 (P(4)-PGF(2alpha)-PMSG); (3) C (n=50), yak cows were artificially inseminated at spontaneous estrus. Frozen semen of Holstein and Jersey were used for insemination in Experiment 2. The CR assessed by rectal palpation 35 days after TAI was not different in A (22.6%), B (30.0%) and C (33.3%), but PR was greater in A and B than in C, when based on those cows presented for estrous synchronization programs. It is concluded that P(4)-PGF(2alpha)-PMSG protocol could efficiently induce estrus and result in an acceptable pregnancy rate in postpartum suckled yak cows. This technique and Co-Synch regimen can be applied successfully for TAI of non-suckled yak cows.