Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction I: Structure, Biosynthesis, Physiological Effects, and Its Role in Estrous Synchronization.

GnRH is essential for the regulation of mammalian reproductive processes. It regulates the production and release of pituitary gonadotropins, thereby influencing steroidogenesis and gametogenesis. While primarily produced in the hypothalamus, GnRH is also produced in peripheral organs, such as the gonads and placenta. GnRH analogs, including agonists and antagonists, have been synthesized for the reproductive management of animals and humans. This review focuses on the functions of hypothalamic GnRH in the reproductive processes of cattle. In addition to inducing the surge release of LH, the pulsatile secretion of GnRH stimulates the pituitary gland to release FSH and LH, thereby regulating gonadal function. Various GnRH-based products have been synthesized to increase their potency and efficacy in regulating reproductive functions. This review article describes the chemical structures of GnRH and its agonists. This discussion extends to the gene expression of GnRH in the hypothalamus, highlighting its pivotal role in regulating the reproductive process. Furthermore, GnRH is involved in regulating ovarian follicular development and luteal phase support, and estrus synchronization is involved. A comprehensive understanding of the role of GnRH and its analogs in the modulation of reproductive processes is essential for optimizing animal reproduction.

A Subovulatory Dose of Human Chorionic Gonadotropin (hCG) May Sustain Terminal Follicle Development and Reproductive Efficiency during Anestrus in Sheep.

The study tested the hypothesis that a single administration of hCG supports the LH-dependent phase of terminal follicular development in synchronized sheep during anestrus, using eCG as a functional reference. Using a clinical approach, four experiments were designed to achieve the following: (1) Identify the inhibitory influence of anestrus on reproduction efficiency; (2) Assess the potential of hCG to keep functional blood concentrations after a single dose; (3) Characterize the effect of different doses of hCG on reproductive functional markers; (4) To compare the ability of hCG to that of eCG to support follicular development and fertility based on the same markers. The results showed that anestrus seems to affect follicular and luteal function under LH dependency as FSH-dependent markers are not compromised; hCG maintains higher blood concentrations than controls for at least 48 h; hCG improves follicular development and ovulatory rates compared to controls and at standards comparable to a breeding season; and ewes treated with hCG exhibit similar performance to those treated with eCG. Our results conclude that hCG can be used to support follicular function during anestrus in sheep, aiming to perfect its regulation in assisted reproduction.

Effect of 200 µg of gonadorelin hydrochloride at the first GnRH of a CIDR Synch program on ovulation rate and pregnancies per AI in Holstein heifers.

The initial ovulatory response during synchronization programs is often low in dairy heifers, largely due to follicular dynamics and hormonal dynamics. Specifically, the progesterone concentration (P4) at the time of the first GnRH treatment in a breeding program can influence the LH response, often resulting in a suboptimal ovulatory response. The objective of this study was to determine the effect of the highest label dose 200 µg (100 µg vs. 200 µg) of GnRH (50 µg gonadorelin hydrochloride per mL; Factrel®; Zoetis Inc. Madison, NJ) at the first GnRH of a 6-d CoSynch plus P4 device program on ovulatory response and pregnancy per AI (P/AI) in first service in Holstein heifers. A total of 1308 Holstein heifers were randomly allocated at the beginning of a 6-d CIDR-Synch program, Day 0, to receive either i.m. treatment of 100 µg (2CC, n = 655) or 200 µg (4CC, n = 653) of GnRH. Also, at Day 0, heifers received an intravaginal insert with 1.38 g of P4 (Eazi-Breed CIDR® Cattle Insert; Zoetis Inc., Madison, NJ). On Day 6, the insert was removed, and i.m. treatment of 25 mg of PGF2α (12.5 mg dinoprost tromethamine/mL; Lutalyse® HighCon Injection Zoetis) was administered. On Day 7, a second i.m. treatment of 25 mg of PGF2α was given, followed on Day 9 by concurrent i.m. treatment of 100 µg of GnRH and timed AI (TAI). A subset of 396 heifers had their ovaries scanned to evaluate ovulatory response, and blood samples were collected to measure the serum concentration of P4 at Day 0 and Day 6 of the study. The P4 concentrations at Day 0 were categorized as Low (≤3ng/mL) or High (>3ng/mL). The ovulatory response was greater for heifers receiving 4CC than 2CC at Day 0 (54.7% vs. 42.8%). The ovulatory response was greater for Low P4 than High P4 at Day 0 (54.3% vs. 37.8%). However, there was not an interaction between treatment and P4 concentrations (Low P4 2CC = 48.6% vs. High P4 2CC = 30.0%; Low P4 4CC = 60.0% vs. High P4 4CC = 45.5%). The ROC curve analysis indicates that P4 concentrations at Day 0 treatment could predict the ovulatory response, although the area under the curve was only 0.6. As expected, heifers that ovulated had increased P/AI (No = 55.6% vs. Yes = 67.7%); however, there was no effect of treatment on P/AI (2CC = 63.3% vs. 4CC = 59.6%), nor interactions between treatment and ovulation and treatment and P4 (HIGH vs LOW) for pregnancy outcomes. In summary, P4 concentration and increasing the dose of GnRH at Day 0 positively impacted ovulatory response in Holstein heifers. However, there was no interaction between treatment and P4 on ovulation and no subsequent impact of GnRH dose on P/AI.

Implementing Fixed-Time Artificial Insemination Programs in Beef Herds.

The article discusses the importance of reproductive biotechnologies, including artificial insemination and fixed-time artificial insemination (TAI), in beef cow-calf operations. The use of TAI improves cow-calf productivity and profitability by shortening the breeding season and increasing the number of calves born earlier, resulting in heavier calves at weaning. However, adoption of TAI by beef producers in the United States has been slow compared with the dairy industry and internationally, such as Brazil. Current TAI protocols are effective in synchronizing ovulation and yield consistent pregnancy results. Factors affecting the success of TAI include cow/heifer factors, sire, nutritional status, and cattle temperament.

Considerations for Using Natural Service with Estrous Synchronization Programs.

Estrous synchronization, coupled with natural service, provides the benefit of female cows conceiving early, but there are an increased number of females expressing estrus in a short period of time. Thus, considerations need to be made for the bull. Select a protocol that will distribute estrus over a longer period of time and ensure bulls pass a breeding soundness examination. Mature bulls (3 years old or older) have increased efficiency in getting cows pregnant compared with younger bulls; therefore, a ratio of 1 mature bull to 25 cows is a good recommendation within an estrous synchronized herd.

Effects of intravaginal administration of prostaglandin F2α on luteolysis and subsequent estrus in Shiba goats (Capra hircus).

This study examined the effects of intravaginal administration of prostaglandin F2α (PGF2α ) on luteolysis and subsequent estrus in cycling goats. Goats with functional corpus lutea received one of five treatments: 2 mg of PG intramuscularly (IM2 × 1; n = 6), 2 mg of PGF2α intravaginally (IVG2 × 1; n = 7), 4 mg of PGF2α intravaginally (IVG4 × 1; n = 7), and 1 or 2 mg of PGF2α intravaginally 8 h apart (IVG1 × 2 group; n = 6 and IVG2 × 2; n = 8). Blood samples were collected at 24-h intervals from 0 to 7 days after PGF2α administration. Estrus was checked twice daily during the experiment. The proportion of goats with complete luteolysis (reduction of progesterone concentrations to <1 ng/mL until 48 h after treatment) in the IVG2 × 1 group (28.6%) was significantly lower than in the other groups (IM2 × 1; 100%, IVG4 × 1; 57.1%, IVG1 × 2; 87.5%, IVG2 × 2; 100%, respectively). For goats completing luteolysis, there was no significant difference in the onset and duration of estrus among the groups. These results suggest that intravaginal administration of PGF2α can be applied as an alternative to intramuscular administration.

Recent advances in treatments for resynchronization of ovulation in small ruminants: a review.

Hormonal methodologies to control small ruminants' estrous cycle are worldwide used and evolved, adjusting the application to the precise female physiological moments to enhance reproductive performance. The estrous cycle can be induced and/or synchronized, aiming for fixed-time artificial insemination, or based on estrus behavior signs for insemination, natural or guided mating. Successive protocols can be performed to resynchronize ovulation and increase reproductive outcomes in females that failed to conceive. These recently developed treatments aim to resynchronize the ovulation as earlier as non-pregnancy is detected. The present review aimed to summarize the recent advances and main findings regarding resynchronization protocols used in small ruminants. Lastly, we present future perspectives and new paths to be studied in the subject. The resynchronization treatment is still a growing field in small ruminant reproduction, nevertheless, some enhancements are found in the reproductive outcome, showing that such protocols can be successfully used in sheep and goat production.

Nanodelivery System for Ovsynch Protocol Improves Ovarian Response, Ovarian Blood Flow Doppler Velocities, and Hormonal Profile of Goats.

Fifteen cyclic, multiparous goats were equally stratified and received the common Ovsynch protocol (GPG: intramuscular, IM, injection of 50 mg gonadorelin, followed by an IM injection of 125 µg cloprostenol 7 days later, and a further IM injection of 50 mg gonadorelin 2 days later) or the Ovsynch protocol using nanofabricated hormones with the same dosages (NGPG) or half dosages (HNGPG) of each hormone. The ovarian structures and ovarian and luteal artery hemodynamic indices after each injection of the Ovsynch protocol using B-mode, color, and spectral Doppler scanning were monitored. Levels of blood serum progesterone (P4), estradiol (E2), and nitric oxide (NO) were determined. After the first gonadotrophin-releasing hormone (GnRH) injection, the number of large follicles decreased (p = 0.02) in NGPG and HNGPG, compared with GPG. HNGPG resulted in larger corpus luteum (CL) diameters (p = 0.001), and improved ovarian and luteal blood flow, compared with GPG and NGPG. Both NGPG and HNGPG significantly increased E2 and NO levels compared with GPG. HNGPG increased (p < 0.001) P4 levels compared with GPG, whereas NGPG resulted in an intermediate value. After prostaglandin F2α (PGF2α) injection, HNGPG had the largest diameter of CLs (p = 0.001) and significantly improved ovarian blood flow compared with GPG and NGPG. Both NGPG and HNGPG increased (p = 0.007) NO levels, compared with GPG. E2 level was increased (p = 0.028) in HNGPG, compared with GPG, whereas NGPG resulted in an intermediate value. During the follicular phase, HNGPG increased (p = 0.043) the number of medium follicles, shortened (p = 0.04) the interval to ovulation, and increased (p < 0.001) ovarian artery blood flow and levels (p < 0.001) of blood serum P4, E2, and NO, compared with GPG and NGPG. During the luteal phase, the numbers of CLs were similar among different experimental groups, whereas the diameter of CLs, luteal blood flow, and levels of blood serum P4 and NO increased (p < 0.001) in HNGPG, compared with GPG and NGPG. Conclusively, the nanodelivery system for the Ovsynch protocol could be recommended as a new strategy for improving estrous synchronization outcomes of goats while enabling lower hormone dose administration.

Comparison of Five Protocols of Estrous Synchronization on Reproductive Performance of Hu Sheep.

The purpose of this study is to compare five protocols of estrous synchronization for Hu ewes to obtain the most effective and economical protocol, to apply the advantageous scheme in large-scale sheep farming. Healthy multiparous Hu ewes (n = 150) were randomly divided into five groups, and all ewes were administered fluorogestone acetate (FGA, 45 mg) vaginal sponge. The sponges of the first three groups (Groups I, II, and III) were removed on the 11th day, and 0.1 mg of PGF2α was injected intramuscularly on the ninth day. Group I received 6 µg of gonadotropin-releasing hormone (GnRH) by intramuscular injection at 36th h after withdrawal of the sponge. Group II was injected 330 IU of pregnant mare serum gonadotropin (PMSG) on the ninth day. The combination of 6 µg of GnRH and 330 IU of PMSG was treated in Group III at the same time as Group I and Group II. The sponges of the latter two groups (Groups IV and V) were removed on the 13th day, and 330 IU of PMSG was injected intramuscularly simultaneously. PGF2α (0.1 mg) was administered on the 12th day in Group IV. All ewes were detected for estrus at 24, 36, 48, 60, and 72 h after the sponge removal. The loss of sponge and vaginitis was recorded when the sponge was withdrawn. Cervical artificial insemination (AI) was performed with fresh semen of Dorper rams diluted with skimmed milk. After 30 days of insemination, the conception was detected with a veterinary B-ultrasound scanner. The lambing status of all ewes and the cost of drugs for estrous synchronization in each group were recorded. The results showed the following: (1) on the whole, the average percentage of estrous ewes in the period of 24-36 h and 36-48 h after removal was significantly higher than other three periods and that of the period of 60-72 h was significantly lower than the first three periods after removal; (2) there was no significant difference in percentages of estrous ewes in any of the five time periods, sponge loss rate, vaginitis rate, total percentage of estrous ewes, conception rate, single lambing rate, twinning rate, and multiple lambing rate of ewes among five protocols; (3) total percentage of estrous ewes and conception rate were more than or equal to 80% in the Groups II and III, and the twinning lamb rate of the Group II protocol was 70%; (4) there was no difference in lambing rate of ewes among Groups II, III, IV, and V; (5) the Group III had the highest drug cost of 22.5 CNY. In conclusion, considering the lambing rate, twinning lamb rate, and drug cost for estrous synchronization, Group II was the most advisable for application and promotion in large-scale sheep farms among these five protocols of estrus synchronization.

Efficacy of estradiol or GnRH in combination with progesterone intravaginal devices to control the follicular wave dynamics and resulting fertility in lactating dairy cows.

This study was conducted to compare efficacy of treatments with EB or GnRH and different quantities of exogenous progesterone (P4) for synchronization of time of ovulation on follicular growth and pregnancy in lactating dairy cows. In Experiment 1, 40 cows were treated with EB or GnRH and 1.9 or 3.0 g of P4 via progesterone-containing intravaginal devices (IVPD; D0), two doses of PGF2α on D7, GnRH on D9, and TAI on D10. In Experiment 2, 1,440 cows were treated with EB or GnRH and 1 g IVPD on D0, cloprostenol, eCG and EB on D7. Cows in estrus by 48 h were AIDE, and non-estrous cows were administered GnRH and TAI 60 h after IVPD removal. Non-estrous cows were AIDE 72 h after IVPD removal. In Experiment 1, P4 was greater on D7 for cows treated with GnRH than those treated with EB. The dominant follicle was larger for cows treated with GnRH than those treated with EB. In Experiment 2, for estrous cows, pregnancy per AI was greater in cows AI at 48 h compared to 60 h after IVPD removal for cows treated with GnRH, and greater with AI at 60 h after IVPD removal compared to 48 h in EB-treated cows. In non-estrous cows, there was no effect on pregnancy. In conclusion, treatment with GnRH compared with EB resulted in increased P4 regardless of amount of exogenous P4, and there were differential proportions of estrous cows pregnant depending on time of AI after IVPD removal.

Addition of eCG to a 14 d prostaglandin treatment regimen in sheep FTAI programs.

In the present study, there was evaluation of the alternative of adding eCG as part of a long-interval prostaglandin-F2α (PG) treatment on the reproductive efficiency of Merino sheep during the breeding season. A total of 210 ewes and 182 ewe lambs were randomly assigned to three experimental groups to induce the timing of estrus among ewes in a: Long-interval PG, group being synchronized using two doses of PG 14 days apart; Long-interval PG + eCG group being synchronized using the same treatment regimen as Group PG with the addition of 200 IU eCG to the regimen, administered concomitantly with the second PG administration; and MAP + eCG group being synchronized with intravaginal progestin sponges for 14 days plus 200 IU eCG, administered at the time of sponge removal. The percentage pregnancy rate in ewes of the MAP + eCG group was greater than the ewes of the Long-interval PG and Long-interval PG + eCG groups (76.4 % compared with 52.0 % and 62.5 %, respectively; P < 0.05). The prolificacy rate was greater in the ewes of the Long-interval PG+eCG group compared with the other groups (114 % compared with 100 % and 103 %, respectively; P < 0.05). When considering the fecundity rate, ewes of the Long-interval PG+eCG and MAP+eCG groups had greater values than ewes of the Long-interval PG group (71.2 % and 78.8 % compared with 52.0 %, respectively; P < 0.05). The Long-interval PG+eCG is an alternative to the conventional progestin sponge plus eCG treatment regimen with there being a greater fecundity rate when this regimen is used compared with the Long-term PG and similar to MAP-eCG treatment regimens.

Identification and characterization of putative ovarian lincRNAs in dairy goats treated for repeated estrous synchronization.

The goal of this study was to identify and characterize effects of repeated estrous synchronization (ES) treatments on the regulation of ovarian intergenic long non-coding RNAs (lincRNAs) in dairy goats. Six does were randomly assigned to a group administered three ES treatment regimens separated by 2 weeks or to a group administered only one ES treatment regimen (control) at the same time as the third ES treatment in the does administered the three hormonal regimens for ES. The paired-end RNA Sequencing procedures were used to evaluate lincRNAs of ovarian tissues. A total of 134 lincRNAs were differentially abundant between the two treatment groups. Several target genes were annotated and were related to hormone activity, cellular response to hormone stimulus, response to hormone, female pregnancy, as well as regulation of hormone secretion. These genes were noticeably enriched in MAPK, Hippo, estrogen signaling pathways, oocyte meiosis, progesterone-mediated oocyte maturation, ovarian steroidogenesis as well as GnRH signaling pathways. According to the enriched GO terms and KEGG pathways of regulated genes, 13 differentially abundant lincRNAs could be promising candidates for regulating reproductive functions of female goats. Current results indicate that repeated treatments with gonadotropins affected hormone sensitivity, estrogen synthesis, and ovarian function. The results also indicated that when there was imposing of the three hormonal treatment regimens for ES, there were several lincRNAs that could contribute to dysregulation of several genes that are important for reproduction in dairy goats. Findings provide novel insights for further investigation of lncRNAs biological functions in goats.

Estrous response and pregnancy percentages following use of a progesterone-based, split-time estrous synchronization treatment regimens in beef heifers.

Mean estrous response rate (%ERR) and pregnancy/AI percentages (%P/AI) were determined after imposing split-time AI (STAI) and fixed time AI (FTAI) following 14-d controlled internal drug release (CIDR)+PGF2α or 5-d Select Synch + CIDR regimens. In Experiment 1, 1152 heifers (five locations) were randomly assigned to 14- or 5-d and to 54 + 74- or 64 + 84-h STAI treatment combinations. Estrous detection patches were affixed at PGF2α administration (19 day after- and on day 5 at- CIDR removal for 14- and 5-d regimens, respectively), assessed at 54- or 64-h and again at 74- or 84-h after PGF2α. Heifers determined to be in estrus at respective times were inseminated and non-estrous heifers at 74- or 84-h were given GnRH and inseminated concomitantly. The %ERR between 54 + 74- and 64 + 84-h STAI combinations differed (73.2 % and 78.8 %, respectively; P < 0.05), but %P/AI did not. In Experiment 2, 2014 heifers (eight locations) were randomly assigned to 14- or 5-d regimens and were inseminated split-time (64+84-h combination, similar to Experiment 1) or at fixed time (72- or 56-h after PGF2α for 14- or 5-d regimens, respectively). There were differences (P < 0.01) between STAI and FTAI treatments for %ERR (81.3 % and 64.4 %) and %P/AI (61.2 % and 55.4 %). Estrous synchronization regimen by AI treatment interaction (P < 0.05) showed that the %ERR were 79.8 %, 82.6 %, 66.2 % and 62.8 % and the %P/AI were 58.9 %, 63.4 %, 56.5 % and 56.5 % (for 14-d/STAI, 5-d/STAI, 14-d/FTAI and 5-d/FTAI, respectively). In conclusion, the 5-d CIDR with 64+84-h STAI combination was the most effective because of the greater %P/AI when this regimen was imposed.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers.

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F2α (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278. Fertile bulls were placed in pastures with heifers of the three NS treatment groups for a 65-day period which began 10 days after progestin treatments (MGA or CIDR) ended. Heifers in FTAI treatment groups were administered PG (25 mg, IM) 16 days after CIDR removal or 19 days following MGA withdrawal, respectively, and FTAI was performed at 66 (CIDR-PG) or 72 h (MGA-PG) after PG. Gonadotropin-releasing hormone (GnRH; 100 µg, i.m.) was administered at FTAI. Pregnancy status was determined at the end of a 65-day breeding period. Pregnancy rates on Days 21 and 65 of the breeding period differed among treatment groups based on pre-treatment pubertal status (P ≤ 0.02) and body weight (P ≤ 0.05) but did not differ by group. These data highlight the need for continued research efforts to improve reproductive management of Bos indicus-influenced females.

Evaluation of estrous synchronization protocols on ewe reproductive efficiency and profitability.

A 2-year experiment was conducted to determine the effect of a single injection of prostaglandin after initiation of the breeding season on ewe estrous synchronization. Rambouillet ewes (n = 101; Year 1 = 52; Year 2 = 49) assigned to one of three treatments: untreated (CON); 12-d CIDR insert (CIDR); or 1 injection of prostaglandin at d 2.5 (1 PG) after rams were placed with ewes. Rams were placed with ewes at the time of CIDR removal (d 0) and remained with ewes during a 35-d breeding season. Both the CIDR- (94%) and 1 PG (73.5%) treatment groups had a larger number (P ≤ 0.01) of ewes bred in the first 5 d of the breeding season compared to ewes of the control (33%) group. As expected, CIDR-treated ewes had a shorter time to mating, than 1 PG-treated ewes and ewes of the control group had a longer interval to mating than both CIDR- and 1 PG-treated ewes (P ≤ 0.01). The number of lambs born per ewe and kg of lamb weaned per ewe was not different (P ≥ 0.31) among treatment groups. Additionally, there was no difference (P =  0.78) in net profit per ewe among treatment groups. Based on these data, utilizing a single injection of PG 2.5 d after initiation of the breeding season resulted in similar pregnancy rates at d 5 of the breeding season when compared with CIDR-treated ewes indicating the potential utilization of the 1PG protocol in a confinement setting as a viable method for estrous synchronization.

Effect of induction of ovulation with estradiol benzoate at P4 device removal on ovulation rate and fertility in Bos indicus cows submitted to a TAI protocol.

This study aimed to minimize the number of times cattle need to be confined during protocols for TAI in beef cows treated for induction of ovulation with EB at the time of P4 device removal (P4r). In Experiment 1, cows were treated with P4 plus EB (Day 0; AM) and were allocated to one of three groups at P4r: EB8.5, EB at P4r on Day 8.5 (PM; three confinements); EB9, EB 24 h after P4r on Day 8 (AM; four confinements) and EC8, EC at P4r on Day 8 (AM; positive control; three confinements). At P4r, cows were treated with PGF2a plus eCG. Ultrasonography was performed from D8 to D12. The interval from P4r to ovulation was less in the EB8.5 compared to EB9 and EC8 group. There was no difference in the ovulation rate between groups. The variability of ovulation was greater in the EB8.5 and EC8 compared to EB9 group. In Experiment 2, cows of EC8 and EB9 groups were submitted to TAI 48 to 52 h (AM) or 54 to 58 h (PM) after P4r (D10). Cows of the EB8.5 group were submitted to TAI 38 to 42 h (AM) or 44 to 48 h (PM) after P4r (D10). There was no interaction between treatments and timing of AI and no treatment effect and timing of AI on P/AI. In conclusion, the delay compared to what typically occurs by 10 h of P4r concomitant with EB administration (Day 8.5) reduced the frequency of animal confinement for the TAI protocol without affecting the reproductive efficiency and the flexibility to perform the TAI in suckled beef cows.

Evaluation of embryo collection and transfer days on pregnancy rate of Mangalarga Marchador mares during the breeding season / Evaluación de los días de recolección y transferencia de embriones sobre las tasas de preñez en yeguas Mangalarga Marchador durante la estación de monta / Avaliação do dia da colheita e da transferência de embriões equino da raça Mangalarga Marchador durante a estação de monta

Abstract Background: Proper timing for embryo collection and transfer in horses -which is critical for the success of this biotechnology- is still debated. Additionally, there is little information on this technology under tropical conditions. Objective: To determine the best day for collection and transfer of embryos in Mangalarga Marchador mares under Brazilian northeast's conditions. Methods: Donors (n= 30) and recipients (n= 76) in diestrus phase were selected based on both clinical and gynecology examinations. Estrus was induced on both donor and recipient mares by intramuscular injection of 5 mg Dinoprost, aiming to obtain an ovulation interval of -1 to +3 between recipient and donor. Ovulation was induced with buserelin acetate when the largest follicle reached at least 35 mm in diameter. At this time, mares were subjected to artificial insemination at 48-hour intervals until ovulation. The embryos were collected on days 7, 8, and 9 after ovulation. Results: The embryo collection on day 8 was more efficient (p<0.05) than on day 7, but it was not more effective (p>0.05) than day 9, which presented the same efficiency (p>0.05) as day 7. From a total of 76 embryos transferred to the recipients, that were between days 4 and 9 after ovulation, there was no influence (p>0.05) of the day of transfer on pregnancy rate. Conclusions: The embryo collection must be performed on day 8 after ovulation, and transfer can be performed on any day of that interval (4-9) without affecting the pregnancy rate.

Resumen Antecedentes: El momento mas apropiado para la recolección y transferencia de embriones en equinos -que es fundamental para el éxito de esta biotecnología- continua siendo sujeto de estudio. Además, es escasa la información sobre esta tecnología en condiciones tropicales. Objetivo: Determinar el momento mas adecuado para la recolecta y transferencia de embriones en yeguas Mangalarga Marchador, en las condiciones del nordeste Brasileño. Métodos: Donadoras (n= 30) y receptoras (n= 76) en la fase de diestro se seleccionaron con base en los exámenes clínicos y ginecológicos. El estro de las yeguas donadoras y receptoras fue inducido con 5 mg de Dinoprost, vía intramuscular, intentando obtener un intervalo de ovulación de -1 a +3 entre la receptora y la donadora. La ovulación fue inducida con acetato de buserelina cuando el folículo mayor alcanzó 35 mm de diámetro. En ese momento, las yeguas fueron sometidas a inseminación artificial en intervalos de 48 horas hasta la ovulación. Los embriones fueron recolectados en los días 7, 8 y 9 después de la ovulación. Resultados: La recolecta de embriones en el día 8 fue más eficiente (p<0,05) que en el día 7, pero no fue más efectivo (p>0,05) que en el día 9, el cuál presentó la misma eficiencia (p>0,05) que en el día 7. De un total de 76 embriones transferidos a las receptoras, que se encontraban entre el día 4 y 9 después de la ovulación, no se registró influencia (p>0,05) del día de la transferencia en la tasa de preñez. Conclusiones: La recolecta embrionaria debe ser realizada el día 8 después de la ovulación, y la transferencia puede ser realizada en cualquier día de este intervalo (4 a 9) sin que se afecte la tasa de preñez.

Resumo Antecedentes: A importância do momentoda colheita e da transferência do embrião equino para o sucesso dessa biotécnica em equino continua sem ser completamente entendida. Adicionalmente, existe pouca informação sobre essa tecnologia em condições tropicais. Objetivo: Determinar o melhor dia para colheita e para transferência de embriões em eguas manga larga marchador nas condições do nordeste brasileiro. Métodos: Doadoras (n = 30) e receptoras (n = 76) na fase de diestro foram selecionadas com base nos exames clínico e ginecológicos. O estro das éguas doadoras e receptoras foi induzido com 5 mg de Dinoprost administrado por via intramuscular, buscando obter um intervalo de ovulação de -1 a +3 entre a receptora e a doadora. A ovulação foi induzida com acetato de buserelina quando o foliculo maior alcançou o tamanho de 35 mm de diâmetro. Nesse momento, as éguas foram submetidas a inseminação artificial em intervalos de 48 horas até a ovulação. Os embriões foram colhidos nos dias 7, 8 e 9 depois da ovulação. Resultados: A colheita de embriões no dia 8 foi mais eficiente (p<0,05) do que no dia 7, porem não foi mais efetivo (p>0,05) do que o dia 9, o qual apresentou a mesma eficiência (p>0,05) que o dia 7. De um total de 76 embriões transferidos para as receptoras que se encontravam entre os dias 4 e 9 depois da ovulação, não se registrou influência (p>0,05) do dia da transferência sobre a taxa de prenhez. Conclusões: A colheita embrionária deve ser realizada no dia 8 depois da ovulação, e a transferência pode ser realizada em qualquer dia desse intervalo (4-9) sem que a taxa de prenhez seja afetada.

Effect of dietary supplementation of palm kernel cake on ovarian and hepatic function in buffalo (Bubalus bubalis).

To determine the optimal inclusion amount of palm kernel cake (PKC) in a buffalo diet, in the present study there was evaluation of the ovarian activity, metabolism and hepatic function of females that were treated to synchronize the time of ovulation. Twenty-four estrous-cyclic and non-lactating Murrah buffalo with a mean age of 5.7 years were supplemented with 0%, 0.25%, 0.5% and 1% of their body weight (BW) with PKC. Animals were subjected to the Ovsynch protocol (beginning of protocol = D0). The ovaries were examined and the blood was collected on D10 (follicular phase) and D17 (luteal phase). Follicular and luteal development and serum progesterone concentrations were not affected by diet (P > 0.05). Serum concentrations of cholesterol were greater in animals supplemented with PKC in amounts at 0.5% of BW or less with PKC, regardless of the phase of the estrous cycles when evaluations occurred (P < 0.05). Concentrations of HDL-cholesterol were similar (P > 0.05) during the follicular and luteal phases. Triglyceride concentrations increased linearly (P = 0.03) as percentage of PKC inclusion diets increased during the follicular phase, but were similar in the luteal phase (60.0 mg/dL; P = 0.51). Amount of PKC supplementation did not affect the concentrations of alanine aminotransferase, but there was a greater amount of aspartate aminotransferase (AST) and gamma glutamyl transferase (GGT) during both phases of the estrous cycle (P < 0.05). Animals supplemented at 1.0% of BW with PKC had greater AST and GGT concentrations than what is recommended for buffalo. The results of the present study indicate PKC supplementation of buffalo diets does not affect the development of the ovarian follicle and corpus luteum nor the peripheral concentration of progesterone, even though there are greater serum concentrations of total cholesterol and triglycerides. Because the amount of PKC supplementation in the present study does not result in hepatic dysfunction when fed at the 0.5% of BW amount, it is suggested that this agro-industrial byproduct of high nutritional value may be a new alternative for dietary supplementation of grazing buffalo.

A two-injection prostaglandin F2α presynchronization treatment decreases pregnancy rates of cycling replacement beef heifers.

Improving artificial insemination (AI) pregnancy rates in replacement heifers improves the genetic advancement within a herd. Heifers that have completed at least three estrous cycles prior to breeding have greater pregnancy rates compared to acyclic females. Therefore, it was hypothesized that a presynchronization treatment program consisting of two injections of prostaglandin F2α (PGF2α) prior to the start of the CO-Synch + 5 d CIDR protocol would initiate earlier attainment of puberty and more estrous cycles prior to AI, thus increasing AI pregnancy rates. All heifers were managed the same at two locations over the course of 2 yr. Heifers were randomly assigned to receive either the two-injection PGF2α presynchronization treatment (PreSynch; n = 105) or no presynchronization (Control; n = 106) prior to the start of estrous synchronization. On the first day of the trial, reproductive tract scores (RTSs), pelvic areas, body condition scores, and weights were collected on all heifers. All heifers were synchronized with the CO-Synch + 5 d CIDR protocol and fixed-time artificially inseminated with semen from a bull of known fertility. Blood samples were collected three consecutive times at 7 d intervals starting 45 d prior to estrous synchronization to determine the onset of puberty via analyzing progesterone concentrations. Pregnancy status to AI was assessed using ultrasonography diagnosis at approximately 30 and 60 d post insemination. Data were analyzed using PROC MIXED of SAS and reported as least square mean. The PreSynch treatment decreased AI pregnancy rates (52.2% vs. 38.1 ± 6.3% for Control vs. PreSynch, respectively; P = 0.06) and did not result in earlier attainment of puberty in beef heifers (P > 0.05). The PreSynch treatment did not impact pregnancy rates in heifers with an RTS of 3 or 4 (P > 0.05). However, PreSynch heifers with an RTS of 5 had decreased pregnancy rates (68.3% vs. 46.9 ± 10.1% for Control vs. PreSynch, respectively; P < 0.05). Finally, PreSynch heifers with increased body condition of 6 had decreased pregnancy rates when compared to Control heifers (37.5% vs. 62.5 ± 11.6%, respectively; P < 0.05). On the basis of these data, implementation of heifer breeding soundness examination at least 3 wk prior to the start of the breeding season may be beneficial for selecting replacement females; however, presynchronization with prostaglandins immediately prior to estrous synchronization will negatively affect AI pregnancy rates in cycling pubertal heifers.

Effects of short-term intravaginal progestagens on the onset and features of estrus, preovulatory LH surge and ovulation in sheep.

In the present study, there was a comparison among classical long-term progestagen (fluorogestone acetate) protocols for synchronization of estrus and ovulation (14 days; group FGA14, n = 9 ewes) and short-term protocols based on 7 days of progestagen treatment plus a dose of prostaglandin F2α at either insertion (PG-FGA7, n = 11) or removal (FGA7-PG, n = 12). There were no significant differences in the ovulation rate and progesterone secretion among treatments. The FGA7-PG group, however, had a similar percentage of ewes expressing estrous behavior than the group FGA14 (90.9 and 100%, respectively, with a trend for a lesser percentage in the PG-FGA7 group, 63.6%) and about 90% of the ewes in the FGA7-PG group had the preovulatory surge release of LH 8 h after the onset of estrous behavior. These features may be related to a greater number of preovulatory follicles during growing phases (P < 0.05) and a greater plasma estradiol concentration (P < 0.05) in this group than in the classical 14-day group, which suggest these are more functional preovulatory follicles. In conclusion, therefore, the use of the FGA7-PG treatment may favor efficiency of progestagen-based protocols for reproductive management.