Factors affecting success of embryo collection and transfer in large dairy herds

A retrospective analysis of conception per embryo transfer in dairy cattle in South Korea

The bovine embryo production industry has seen significant growth over the past two decades, particularly in the production of in vitro produced embryos. This growth, driven by advancements in cryopreservation, in vitro culture mediums, ovum pick-up (OPU) procedures, ultrasonography devices, and embryo transfer (ET) has been notable. Particularly, ET is crucial for disseminating high genetic merit and amplifying foreign breeds by importing frozen embryos. This retrospective study aimed to assess factors affecting conception per embryo transfer (CPET) in Holstein-Friesian cattle in South Korea from October 2008 to July 2022. We evaluated type of embryo breed, type of embryo production (fresh and frozen; in vitro and in vivo production), recipient conditions including estrus type, corpus luteum quality, parity (nulliparous heifers, primiparous, and multiparous cows), and the daily mean temperature-humidity index (THI) as an index for heat stress. Type of embryo breed and estrus had no significant impact on CPET. However, we observed higher CPET in recipients with good quality corpus luteum, nulliparous heifers, and surrogates receiving fresh in vitro and frozen in vivo embryos. Importantly, CPET was not adversely affected by mild heat stress conditions (up to daily mean THI 76), indicating that using frozen in vivo embryos produced by multiple ovulation embryo transfer and fresh in vitro embryos by OPU-ET can help alleviate the subfertility issues in dairy cattle caused by global warming in Korea.

The effect of progesterone concentrations during superovulation of Holstein heifers in a randomized trial

The aim of this study was to evaluate the effect of different progesterone (P4) concentrations during the follicular growth on the intensity of estrous expression, ovarian response to the superovulatory treatment, and embryo production and quality in superovulated heifers. A total of 63 Holstein heifers were randomly assigned into 2 experimental groups: Low P4 (n = 31) and High P4 (n = 32). Animals received a pre-synchronization protocol followed by a protocol of superovulation that included the allocated P4 treatment. Activity was monitored continuously by an automated activity monitor, and estrus characteristics (maximum intensity and duration) were recorded. Embryo collection was performed 7 d post artificial insemination (AI). Embryos were counted and graded from good or excellent (1) to degenerated (4). The outcomes of interest were: number and diameter of follicles at the time of AI, ovulation success (confirmed 7 d post-AI), time to estrus event, maximum intensity and duration of estrus, number and quality of embryos. Data were analyzed according to the type of outcome variable using logistic, linear, or Poisson regression models. A total of 105 embryos (High P4: n = 42; Low P4: n = 63) were graded for quality. Different P4 levels did not affect the maximum intensity (High P4 = 497.8 ± 23.9%; Low P4 = 542.2 ± 23.5%) or the duration (High P4 = 13.5 ± 1.5 h; Low P4 = 14.3 ± 1.4 h) of estrus. Heifers in the High P4 treatment had greater number of follicles at time of AI (High P4 = 16.6 ± 1.6 follicles; Low P4 = 13.9 ± 1.2 follicles), but with smaller diameter (High P4 = 11.3 ± 0.1 mm; Low P4 = 12.0 ± 0.1 mm) compared with Low P4. High P4 heifers tended to have better embryo quality compared with Low P4 heifers (odds ratio = 1.98; 95% CI = 0.90-4.35). High P4 heifers had less embryos than Low P4 heifers, but this was modified by the CIDR (intravaginal implant of P4) removal to estrus interval (interval 0-21 h: mean ratio = 1.15, 95% CI = 0.42-1.87; interval 22-46 h: mean ratio = 0.58, 95% CI = 0.27-0.96). Although estrous expression was not associated with embryo quality, as the duration and the maximum intensity of estrous expression increased, the number of embryos recovered 7 d post-AI increased (duration: mean ratio = 1.04; 95% CI = 1.03-1.05; maximum intensity: mean ratio = 1.50; 95% CI = 1.42-1.58). In conclusion, P4 during the follicular growth, and intensity of estrus, are playing a role in regulating the quality and the number of embryos produced by superovulated heifers. This study was supported by contributions from Resilient Dairy Genome Project and the Natural Sciences and Engineering Research Council.

Embryo Transfer

Assisted reproductive technologies (ART) have made tremendous advances, in last years. Artificial insemination is a method for achieving slow genetic progress in populations of animals. Many large and small ruminants are bred by AI, and more than a half million embryos are transferred every year around the world. Most of the ruminants sires used for artificial insemination were derived from embryo transfer. Improvements of reproductive biotechnologies of controlling the estrous cycle and ovulation have resulted in more effective programs for AI, superovulation of donor, and the management of ET. In the ruminants, ET procedure is a timely alternative that can allow good conception rates to be obtained constant in a year. There have been great advances of this biotechnique with on aimed to intensify the genetic progress between generations of farm. The gains is possible with the development of advanced reproductive biotechnique. The best current strategy in applying biotechnology to farmers is to use AI with sexed semen, so farmers will enjoy and benefit. The use of ET together with cryopreserved sexed embryos has a very specific potential for donor replacement and genetic improvement of the herd. In this chapter, procedures of the MOET protocol were described step by step.

Heat stress during critical windows of the estrous cycle and risk of pregnancy establishment in embryo-recipient dairy heifers

This study aimed to determine effects of exposure of recipient dairy heifers to heat stress (THI≥ 73) during the estrous cycle coinciding with embryo transfer (ET) on the risk of pregnancy establishment after transfer of in vivo produced embryos. Recipients exposed to THI values ≥ 73 during days zero (recipient estrus), 7 (day of ET), 14 (seven days after ET), 15 and 16 (maternal recognition of pregnancy) of the ET cycle were considered as heat stressed heifers (n=254), while heifers in the control group (n=470) were not exposed to THI≥ 73 at any of the previous days. Results revealed no significant effects of any of the investigated factors on the risk of pregnancy following ET. However, the mean THI above 77 was associated with a drastic numerical decrease in PR/ET (36.63%), when compared to a mean THI 72 (78.78%). In addition, PR/ET after transfer of second and third grade embryos were numerically lower in heat-stressed recipients, compared to first grade embryos (41.17 vs 56.36%, respectively). Our findings confirmed that transfer of blastocysts were associated with numerically higher PR/ET in heat stressed and control recipients, as compared to morula stage. Interestingly, PR/ET tended to be higher when sexed embryos were transferred to the control recipients compared to heat-stressed ones. In conclusion, PR/ET in dairy heifers was not significantly affected by heat stress during critical windows of their estrous cycle coinciding with ET, whereas transfer of sexed embryos gives lower results under conditions of heat stress.

MOET Efficiency in a Spanish Herd of Japanese Black Heifers and Analysis of Environmental and Metabolic Determinants

Multiple ovulation and embryo transfer (MOET) systems have been intensively implemented in Japanese Black cattle in Japan and to create Japanese Black herds out of these areas. Environmental conditions influence MOET efficiency. Thus, we describe results of 137 in vivo, non-surgical embryo flushings performed between 2016-2020, in a full-blood Japanese Black herd kept in Spain and the possible effects of heat, year, bull, donor genetic value, and metabolic condition. Additionally, 687 embryo transfers were studied for conception rate (CR) and recipient related factors. A total of 71.3% of viable embryos (724/1015) were obtained (5.3 ± 4.34/flushing). Donor metabolites did not affect embryo production (p > 0.1), although metabolite differences were observed over the years, and by flushing order, probably related to the donor age. CR was not affected by embryo type (fresh vs. frozen), recipient breed, and whether suckling or not suckling (p > 0.1). CR decreased significantly with heat (44.3 vs. 49.2%; (p = 0.042)) and numerically increased with recipient parity and ET-number. Pregnant recipients showed significantly higher levels of cholesterol-related metabolites, glucose, and urea (p < 0.05). Therefore, adequate MOET efficiency can be achieved under these conditions, and heat stress should be strongly avoided during Japanese Black embryo transfers. Moreover, recipients' metabolites are important to achieve pregnancy, being probably related to better nutrient availability during pregnancy.

Effects of heat stress on the endometrial epidermal growth factor profile and fertility in dairy cows

The endometrial epidermal growth factor (EGF) profile is an indicator of uterine function and fertility in cattle. The present study aimed to investigate the effects of heat stress on the endometrial EGF profile and fertility in lactating Holstein cows. The endometrial EGF profiles of 365 cows in the Hokkaido and Kyushu regions were examined between June and September (heat stress period, n = 211) and between October and January (control period, n = 154). EGF profiles were investigated using uterine endometrial tissues obtained by biopsy 3 days after estrus (Day 3). The proportion of cows with an altered EGF profile was higher between June and September than between October and January (41.2 vs. 16.2%, P < 0.05). The effects of rectal temperature on Days 0 and 3 on the endometrial EGF profile were also assessed in cows (n = 79) between June and September in the Kyushu region. A single embryo was transferred to cow on Day 7 to evaluate fertility (n = 67). Regardless of the rectal temperature on Day 3, the proportion of cows with an altered EGF profile was higher (64.1 vs. 30.0%, P < 0.05) and the pregnancy rate after embryo transfer (ET) was lower (26.7 vs. 51.4%, P < 0.05) in cows with a rectal temperature ≥ 39.5°C on Day 0 than in cows with a rectal temperature < 39.5°C on Day 0. The present results indicate that alterations in the endometrial EGF profile induced by an elevated body temperature on Day 0 contributed to reductions in fertility in lactating dairy cows during the heat stress period.

Occurrence and greater intensity of estrus in recipient lactating dairy cows improve pregnancy per embryo transfer

The aim of this study was to determine the association between occurrence and intensity of estrous expression with pregnancy success in recipient lactating dairy cows subjected to embryo transfer (ET). Two observational studies were conducted. Holstein cows were synchronized using the same timed ET protocol, based on estradiol and progesterone in both experiments. At 9 d after the end of the timed ET protocol only animals that had ovulated were implanted with a 7-d embryo [experiment 1 (Exp. 1); n = 1,401 ET events from 1,045 cows, and experiment 2 (Exp. 2); n = 1,147 ET events from 657 cows]. Embryos were produced in vivo (Exp. 1 and Exp. 2) and in vitro (only Exp. 2), then transferred to recipient cows as fresh or frozen-thawed. Pregnancy was confirmed at 29 and 58 d after the end of timed ET protocol. In Exp. 1, animals had their estrous expression monitored through a tail chalk applied on the tail head of the cows and evaluated daily for chalk removal (no estrus: 100% of chalk remaining; estrus: <50% of chalk remaining). In Exp. 2, cows were continuously monitored by a leg-mounted automated activity monitor. Estrous expression was quantified using the relative increase in physical activity at estrus in relation to the days before estrus. Estrous expression was classified as no estrus [<100% relative increase in activity (RI)], weak intensity (100-299% RI), and strong intensity (≥300% RI). Data were analyzed by analysis of variance using mixed linear regression models (GLIMMIX) in SAS (SAS Institute Inc.). A total of 65.2% (914/1,401) and 89.2% (1,019/1,142) of cows from Exp. 1 and Exp. 2, respectively, displayed estrus at the end of the ovulation synchronization protocol. In Exp. 1, cows expressing estrus before to ET had greater pregnancy per ET than those that did not [41.0 ± 2.3% (381/914) vs. 31.5 ± 2.9% (151/487), respectively]. Similarly, in Exp. 2, cows classified in the strong intensity group had greater pregnancy per ET compared with cows in the weak intensity and no estrus groups [41.3 ± 2.2% (213/571) vs. 32.7 ± 2.7% (115/353) vs. 11.3 ± 3.5% (26/218), respectively]. There was no effect of ET type on pregnancy per ET in Exp. 1. However, in Exp. 2, cows that received an in vivo-produced embryo, either fresh or frozen, had greater pregnancy per ET compared with cows that received in vitro-produced embryo. Cows receiving embryos in the early blastocyst and blastocyst stage had greater fertility compared with cows receiving embryos in the morula stage. There was an interaction between the occurrence of estrus and the stage of embryo development on pregnancy per ET, cows which displayed estrus and received a morula or early blastocyst had greater pregnancy per ET than cows that did not display estrus. In conclusion, the occurrence and the intensity of estrous expression improved pregnancy per ET in recipient lactating dairy cows and thus could be used as a tool to assist in the decision making of reproduction strategies in dairy farms.

Prospects for increasing the utilization of cattle embryo transfer by small-scale milk and meat producers in tropical regions

Small community cattle farmers in the tropics are facing challenges to deliver quality products whilst under pressure to increase milk and beef yields per cow. These challenges could be partially met by crossbreeding Bos taurus with Bos indicus (F1) cattle utilizing embryo transfer (ET) technology. The Bos taurus infusion would increase milk production, whilst the Bos indicus influence can improve resistance to the harsh environment of the tropics. Here, individuals from existing herds can be used to produce F1 embryos which benefit from hybrid vigour. Resultant female offspring would in turn receive an F1 embryo on reaching breeding maturity. This approach would help to provide a cost-effective, systematic approach to improve productivity in dairy and beef cattle in the tropics. However, full usage of ET, including in vitro applications, in the tropics will require improvements in procedures, resources and education.

Lineage Differentiation Markers as a Proxy for Embryo Viability in Farm Ungulates

Embryonic losses constitute a major burden for reproductive efficiency of farm animals. Pregnancy losses in ungulate species, which include cattle, pigs, sheep and goats, majorly occur during the second week of gestation, when the embryo experiences a series of cell differentiation, proliferation, and migration processes encompassed under the term conceptus elongation. Conceptus elongation takes place following blastocyst hatching and involves a massive proliferation of the extraembryonic membranes trophoblast and hypoblast, and the formation of flat embryonic disc derived from the epiblast, which ultimately gastrulates generating the three germ layers. This process occurs prior to implantation and it is exclusive from ungulates, as embryos from other mammalian species such as rodents or humans implant right after hatching. The critical differences in embryo development between ungulates and mice, the most studied mammalian model, have precluded the identification of the genes governing lineage differentiation in livestock species. Furthermore, conceptus elongation has not been recapitulated in vitro, hindering the study of these cellular events. Luckily, recent advances on transcriptomics, genome modification and post-hatching in vitro culture are shedding light into this largely unknown developmental window, uncovering possible molecular markers to determine embryo quality. In this review, we summarize the events occurring during ungulate pre-implantation development, highlighting recent findings which reveal that several dogmas in Developmental Biology established by knock-out murine models do not hold true for other mammals, including humans and farm animals. The developmental failures associated to in vitro produced embryos in farm animals are also discussed together with Developmental Biology tools to assess embryo quality, including molecular markers to assess proper lineage commitment and a post-hatching in vitro culture system able to directly determine developmental potential circumventing the need of experimental animals.

The incompletely fulfilled promise of embryo transfer in cattle-why aren't pregnancy rates greater and what can we do about it?

Typically, bovine embryos are transferred into recipient females about day 7 after estrus or anticipated ovulation, when the embryo has reached the blastocyst stage of development. All the biological and technical causes for failure of a female to produce a blastocyst 7 d after natural or artificial insemination (AI) are avoided when a blastocyst-stage embryo is transferred into the female. It is reasonable to expect, therefore, that pregnancy success would be higher for embryo transfer (ET) recipients than for inseminated females. This expectation is not usually met unless the recipient is exposed to heat stress or is classified as a repeat-breeder female. Rather, pregnancy success is generally similar for ET and AI. The implication is that either one or more of the technical aspects of ET have not yet been optimized or that underlying female fertility that causes an embryo to die before day 7 also causes it to die later in pregnancy. Improvements in pregnancy success after ET will depend upon making a better embryo, improving uterine receptivity, and forging new tools for production and transfer of embryos. Key to accelerating progress in improving pregnancy rates will be the identification of phenotypes or phenomes that allow the prediction of embryo competence for survival and maternal capacity to support embryonic development.

Effects of follicular ablation and GnRH on synchronization of ovulation and conception rates in embryo recipient heifers

Two experiments were performed to determine effects of follicular ablation (FA) and GnRH treatment on conception rate and synchronization in timing of ovulation among Holstein heifers. In Experiment 1, heifers were randomly allocated to four groups: Control (n = 84): prostaglandin F_2α (PGF) IM on Day 0; FA-5/GnRH (n = 43): FA 5 days before PGF and GnRH on Day 2; FA-4/GnRH (n = 48):FA 4 days before PGF and GnRH on Day 2; andFA-3/GnRH (n = 21): FA 3 days before PGF and GnRH on Day 2. Ultrasonography was performed to determine follicular size, ovulation occurrence, and size of CL. In Experiment 2, heifers were assigned to three groups: Control (n = 264), FA-5/GnRH, and FA-4/GnRH. Pregnancy diagnosis was performed at Days 30 and 60. In Experiment 1, size of largest follicle at time of PGF was less variable (P ≤ 0.05) in all FA groups compared to the Control group. With the FA-5/GnRH and FA-4/GnRH treatments, there were greater (P ≤ 0.05) proportions of timing of ovulation synchronization (86 % and 85 %, respectively) compared to the Control (61 %) and FA-3/GnRH (62 %) groups. In Experiment 2, conception rates did not differ among groups, however, there were more pregnancies per cow when timing-of-ovulation treatments were imposed. In conclusion, follicular ablation combined with GnRH treatment resulted in an increased proportion of heifers having synchronized ovulation and, therefore, number of recipient heifers available for embryo transfer. Additionally, there was no effect on conception rate when there was greater synchronization in timing of ovulation among heifers.

Reproductive Outcomes and Endocrine Profile in Artificially Inseminated versus Embryo Transferred Cows

Simple Summary

Bovine embryos are nowadays produced in laboratories, frozen and transferred to other cows. However, the percentage of pregnancies obtained after these transfers as well as difficulties found during labor, especially due to increased size of calves, are a matter of great concern. One of the possible explanations for these problems relies on the embryo being produced in in vitro conditions (laboratory settings), more specifically the culture medium (liquid) used to develop these embryos. In an attempt to better mimic what happens naturally, female reproductive liquids (from oviducts and uterus) were used as a supplement to the culture of the embryos. As controls, embryos produced using the standard protocol in the laboratory were produced, as well as embryos derived from artificial insemination of cows (in vivo). An evaluation on the pregnancy rates, how the hormonal profile of the recipients changed during pregnancy, difficulties during parturitions, and phenotype of calves were recorded. Results showed that all the groups were very similar, but many differences were noted on the hormonal profiles during pregnancy. In conclusion, all systems provided safe production of calves, but long-term analysis of these calves is necessary to understand the future impact of the laboratory protocols.

Abstract

The increasing use of in vitro embryo production (IVP) followed by embryo transfer (ET), alongside with cryopreservation of embryos, has risen concerns regarding the possible altered pregnancy rates, calving or even neonatal mortality. One of the hypotheses for these alterations is the current culture conditions of the IVP. In an attempt to better mimic the physiological milieu, embryos were produced with female reproductive fluids (RF) as supplements to culture medium, and another group of embryos were supplemented with bovine serum albumin (BSA) as in vitro control. Embryos were cryopreserved and transferred while, in parallel, an in vivo control (artificial insemination, AI) with the same bull used for IVP was included. An overview on pregnancy rates, recipients’ hormonal levels, parturition, and resulting calves were recorded. Results show much similarity between groups in terms of pregnancy rates, gestation length and calves’ weight. Nonetheless, several differences on hormonal levels were noted between recipients carrying AI embryos especially when compared to BSA. Some calving issues and neonatal mortality were observed in both IVP groups. In conclusion, most of the parameters studied were similar between both types of IVP derived embryos and the in vivo-derived embryos, suggesting that the IVP technology used was efficient enough for the safe production of calves.

Factors associated with pregnancy rate in fixed-time embryo transfer in cattle under humid-tropical conditions of México

The objective was to determine the effect of some factors on pregnancy rate of fixed-time embryo transfer (FTET), in cows and heifers kept under Mexican tropical conditions. Recipients females (n=405) grazing in pastures were selected according to breed group (Zebu and crosses), parity (nulliparous and multiparous), body condition score (BCS) and the presence of a corpus luteum (CL). The females were synchronized on day 0 using a progesterone vaginal device and 2 mg estradiol benzoate (EB), two groups were established. Group 1 (conventional protocol) were animals in which the progesterone device was removed on day 7. At this time, also received an injection of 50 mg cloprostenol sodium and 1 mg estradiol cypionate. Animals also received 300 IU (heifers) or 360 IU (cows) of eCG. Group 2 (J-Synch protocol) were animals in which the progesterone device was removed on day 6. Cloprotenol and eCG injections were applied as in Group 1. Additionally, on day 9, animals of group 2 received 0.01 mg buserelin acetate. Embryo transfer of in vivo or in vitro was done on day 16 and pregnancy diagnosis was realized by ultrasonography on days 23 and 53 after FTET. Statistical analyses were carried out using Chi-square tests and logistic regression. Pregnancy rate varied between farms (P<0.05). The highest pregnancy rate was for multiparous cows (66%). The recipient utilization rate was better in the J-Synch protocol (85%), and in vivo embryos (75%) had higher pregnancy rate. The diameter of the follicle and the CL had no effect on pregnancy rate (P>0.05). However, the logistic regression determined that the only significant factor on pregnancy rate was the type of embryo. In conclusion, pregnancy rate in FTET females was higher for in vivo embryos than for in vitro embryos in cows evaluated under humid tropical conditions in Mexico.

Use of embryo transfer to alleviate infertility caused by heat stress

Heat stress (HS) has a pronounced deleterious effect on fertility in dairy herds throughout the world, especially in hot and humid summer months in tropical and subtropical areas. Summer HS reduces feed intake and increases negative energy balance, induces changes in ovarian follicular dynamics, reduces estrus detection rates and alters oviductal function leading to fertilization failure and early embryonic death. Furthermore, oocytes harvested from lactating cows during summer HS have a decreased ability to develop to the blastocyst stage after in vitro fertilization when compared with oocytes harvested during winter. The present manuscript describes the detrimental effect of HS on reproduction, with emphasis on preovulatory oocytes and carry over effects of HS on embryo development and P/AI. Embryo transfer (ET) has been an effective tool to reestablish fertility during HS because it bypasses the damage to the oocyte and early embryo caused by hyperthermia. Therefore, a management strategy to maintain increased fertility throughout the year would be to produce embryos during the cooler months, when oocyte quality is greater, and use them to produce pregnancies during the periods of HS, when oocyte quality is compromised. However, this strategy only can be implemented using cryopreserved embryos, what is still limiting. During the warmer months, the use of heifers or non-lactating cows as oocyte or embryo donors may facilitate embryo production, mainly because of the lesser deleterious effects of HS comparing to lactating cows. Also, genetic selection of donors for thermoregulation ability is one potential strategy to mitigate effects of HS and increase embryo production during the warmer months. These alternatives enable the transference of fresh embryos with more efficiency during HS periods. Additionally, the application of timed ET protocols, which avoid the need for estrus detection in recipients, has facilitated management and improved the efficiency of ET programs during HS.

Short communication: Greater intensity of estrous expression is associated with improved embryo viability from superovulated Holstein heifers

The aim of this study was to determine the association between estrous expression, measured using a breeding indicator and an automated activity monitor (AAM), and the success of embryo collection after superovulation. Holstein heifers (n = 51; 10.5 to 14.5 mo, and 325.0 ± 21.1 kg of body weight) were superovulated (n = 69 events) for the collection of embryos using a protocol based on sequential administration of FSH for follicle superstimulation and GnRH to induce ovulation. Artificial insemination (AI) was performed twice, once at the moment of GnRH administration and again 12 h later, using thawed, sexed semen. Ovaries were scanned via ultrasonography on the day of the first AI to count the total number of preovulatory follicles and 7 d later for the total number of corpora lutea present. Embryos were collected 7 d post-AI, counted, and assessed for viability. A breeding indicator (Estrotect, Rockway Inc., Spring Valley, WI) and a collar-mounted AAM (CowScout Activity Monitoring System, GEA, Dusseldorf, Germany) were used to measure standing mounts and an algorithmic estimate of estrous expression, respectively. A score for the breeding indicator was given as follows: score 1 = 100% of the indicator was intact; score 2 = 50% of the indicator was rubbed off; score 3 = greater than 50% of the indicator was rubbed off. Estrous expression detected by the AAM was quantified through the relative increase in physical activity and duration of time spent above a set threshold. Data were analyzed by ANOVA using the MIXED procedures of SAS (SAS Institute Inc., Cary, NC). The number of follicles present at AI was not affected by estrous expression. The mean (± SD) ovulatory response was 67.5 ± 26.3%. We found an effect of estrous expression as detected by the breeding indicator on the ovulatory response (42.1 ± 8.0, vs. 78.2 ± 9.0, vs. 74.0 ± 4.9%, for scores 1, 2, and 3, respectively) but not from the AAM. Heifers that had a score of 3 (versus those with scores of 1 and 2) on the breeding indicator had a greater number of embryos (4.1 ± 0.5, vs. 1.2 ± 1.0, vs. 1.8 ± 1.0 embryos), and a greater percentage of these embryos were viable (43.1 ± 0.05, vs. 35.5 ± 0.1, vs. 34.3 ± 0.1%). Similarly, heifers that showed a greater intensity of activity (as measured by the AAM) had a greater number of embryos collected (10.2 ± 1.2 vs. 6.0 ± 1.3 embryos), and a greater percentage of those embryos were viable (53.1 ± 5.0 vs. 23.4 ± 5.1%). Longer-duration estrus episodes were associated with a higher percentage of viable embryos (51.2 ± 5.2 vs. 25.3 ± 5.3%). In conclusion, stronger estrous intensity was associated with a greater number of total embryos collected and a greater percentage of viable embryos. These results suggest that monitoring the intensity of estrus could be used to predict superovulatory response as well as embryo quality in Holstein heifers.

Reproductive physiology of the heat-stressed dairy cow: implications for fertility and assisted reproduction

Heat stress causes a large decline in pregnancy success per insemination during warm times of the year. Improvements in fertility are possible by exploiting knowledge about how heat stress affects the reproductive process. The oocyte can be damaged by heat stress at the earliest stages of folliculogenesis and remains sensitive to heat stress in the peri-ovulatory period. Changes in oocyte quality due to heat stress are the result of altered patterns of folliculogenesis and, possibly, direct effects of elevated body temperature on the oocyte. While adverse effects of elevated temperature on the oocyte have been observed in vitro, local cooling of the ovary and protective effects of follicular fluid may limit these actions in vivo. Heat stress can also compromise fertilization rate. The first seven days of embryonic development are very susceptible to disruption by heat stress. During these seven days, the embryo undergoes a rapid change in sensitivity to heat stress from being very sensitive (2- to 4-cell stage) to largely resistant (by the morulae stage). Direct actions of elevated temperature on the embryo are likely to be an important mechanism for reduction in embryonic survival caused by heat stress. An effective way to avoid effects of heat stress on the oocyte, fertilization, and early embryo is to bypass the effects through embryo transfer because embryos are typically transferred into females after acquisition of thermal resistance. There may be some opportunity to mitigate effects of heat stress by feeding antioxidants or regulating the endocrine environment of the cow but neither approach has been reduced to practice. The best long-term solution to the problem of heat stress may be to increase genetic resistance of cows to heat stress. Thermotolerance genes exist within dairy breeds and additional genes can be introgressed from other breeds by traditional means or gene editing.

Embryo production in middle-aged and mature Bos taurus × Bos indicus cows induced to multiple ovulation in a tropical environment

The objective of the study was to evaluate embryo production in middle-aged and mature Bos taurus × Bos indicus cows induced to multiple ovulation (MO) in a tropical environment. Twenty-eight cows were assigned into two groups: (1) middle-aged cows = 4-6 years old (n = 13), and (2) mature cows = 8-12 years old (n = 15). All donors received the same MO protocol with follicle-stimulating hormone in decreasing dose during 4 days and two artificial insemination services. Total numbers of corpora lutea at embryo collection, structures collected, and viable embryos obtained, as well as recovery rate, were higher in middle-aged cows compared with mature cows (P < 0.05). A total number of degenerate embryos and unfertilized oocytes, as well as viability rate, were similar in both groups (P > 0.05). In conclusion, the mature cows responded to the MO treatment, but the average of viable embryos recovered per donor was lower than in middle-aged cows. Therefore, the inclusion of cows ≥ 8 years old as donors in MO programs in tropical environments should be avoided.

Effect of addition of l-carnitine to media for oocyte maturation and embryo culture on development and cryotolerance of bovine embryos produced in vitro

The objective of these experiments was to determine the effect of l-carnitine during oocyte maturation or embryo culture on embryo development and cryosurvival. For Experiments 1-3, embryos were produced in vitro using abattoir-derived cumulus-oocyte complexes (COCs). At d 7 after insemination, embryo development was assessed, and blastocyst and expanded blastocyst stage embryos were harvested and subjected to controlled-rate freezing. Post-thaw cryosurvival was determined by re-expansion and hatching rates at 24, 48 and 72 h post-thaw. In Experiment 1, COCs were matured with or without 3.03 mM l-carnitine. There was no effect of l-carnitine supplementation during maturation on embryo development or post-thaw cryosurvival. In experiment 2, presumptive zygotes were cultured in medium supplemented with or without 5% (v/v) fetal bovine serum and l-carnitine at concentrations of 0.0, 0.75, 1.5 and 3.03 mM. There was no effect of l-carnitine treatment on embryo development, but embryos treated with l-carnitine had increased (P ≤ 0.05) post-thaw re-expansion rates, irrespective of concentration. In experiment 3, presumptive zygotes were cultured with or without 0.75 mM l-carnitine from d 1 to d 4, from d 4 to d 7 or for the entire culture period. There was no effect of l-carnitine during culture on embryo development or post-thaw cryosurvival, regardless of the timing of addition. In Experiment 4, COCs were harvested by ovum pick-up from virgin dairy heifers (n = 24) and subjected to in-vitro embryo production with presumptive zygotes cultured with or without 0.75 mM l-carnitine. At d 7 after insemination, morula and blastocyst stage embryos were harvested and subjected to controlled-rate freezing. Lactating Holstein cows (n = 102) were used as recipients and synchronized for timed embryo transfer. At d 7 after anticipated ovulation, a single embryo was thawed and transferred to the ipsilateral uterine horn of each recipient with a corpus luteum. Pregnancy was diagnosed at d 33, 44 and 72 of gestation. l-carnitine had no effect on the percentage of cows pregnant per embryo transfer (P/ET) after transfer of a frozen-thawed embryo. In conclusion, media supplementation with l-carnitine during in vitro embryo production can improve post-thaw cryotolerance as assessed in vitro but had no effect on P/ET after transfer of frozen-thawed embryos.

Genetic merit for fertility traits in Holstein cows: VI. Oocyte developmental competence and embryo development

The hypothesis of this study was that cows with good genetic merit for fertility traits (Fert+) would produce oocytes and embryos of greater quality than cows with poor genetic merit for fertility traits (Fert-) and that mRNA expression of candidate genes would reflect the observed differences in quality. The aim of the study, therefore, was to determine the effect of genetic merit for fertility traits on morphological classification and mRNA abundance of key genes in immature oocytes and cumulus cells following ovum pick-up and in embryos following superovulation, artificial insemination (AI), and uterine flushing. In experiment 1, 17 Fert+ and 11 Fert- cows, ranging from 54 to 84 d in milk, were submitted to ovum pick-up on 4 occasions during a 2-wk period. Recovered cumulus-oocyte complexes (COC) were morphologically graded. Oocytes and cumulus cells were separated, and mRNA abundance of genes associated with oocyte developmental competence was measured. There was no effect of genotype on the distribution of COC grades or on the mRNA abundance of the candidate genes in grade 1 COC. In experiment 2, 20 Fert+ and 19 Fert- cows, ranging from 71 to 189 d in milk, were submitted to superovulation and AI. The uteri of cows that responded to the superovulation protocol (17 Fert+ and 16 Fert- cows) were nonsurgically flushed 7 d postovulation. Recovered embryos were morphologically graded, and mRNA abundance of genes associated with embryo development was measured in grade 1 blastocysts. The response to the superovulation protocol was assessed by counting the number of codominant follicles on the day of AI, which was similar for both genotypes (22.0 ± 9.7 and 19.8 ± 8.2 for Fert+ and Fert- cows, respectively). There was no effect of genotype on the proportion of transferable embryos recovered or on the mRNA abundance of the candidate genes tested in the grade 1 blastocysts. Of the total embryos classified as blastocysts, however, the Fert+ cows tended to have a greater proportion of grade 1 blastocysts compared with Fert- cows (90% vs. 64%, respectively). In conclusion, genetic merit for fertility traits had a no effect on mRNA abundance of the candidate genes that were examined in immature oocytes and cumulus cells and in embryos recovered after superovulation. The observed differences in morphological blastocyst quality following superovulation would suggest that the superior reproductive performance of Fert+ cows could arise during the later stages of embryo development from d 7 until maternal recognition of pregnancy.

Effect of treatment with human chorionic gonadotropin 7 days after artificial insemination or at the time of embryo transfer on reproductive outcomes in nulliparous Holstein heifers

Our objective was to assess the effect of treatment with human chorionic gonadotropin (hCG) 7 d after artificial insemination (AI) or at the time of in vitro-fertilized (IVF) embryo transfer on reproductive outcomes, including progesterone (P4), interferon-tau stimulated gene 15 (ISG15), pregnancy-specific protein B (PSPB), and pregnancies per AI (P/AI) or pregnancies per embryo transfer (P/ET), in nulliparous Holstein heifers. Heifers in experiment 1 were randomly assigned to receive no treatment (control; n = 129) or 2,000 IU of hCG 7 d after AI to a detected estrus (estrus = experimental d 0; hCG; n = 132). Heifers in experiment 2 were randomly assigned to receive no treatment (control; n = 143) or 2,000 IU of hCG (hCG; n = 148) at transfer of an IVF embryo 7 d after the last GnRH treatment of a 5-d controlled internal drug release-synch protocol (last GnRH = experimental d 0). Blood samples were collected from a subgroup of heifers (experiment 1, n = 82; experiment 2, n = 104) at d 7, 11, 18, 20, 25, 28, and 32, and blood samples from heifers diagnosed pregnant were collected on d 35, 39, 46, 53, 60, and 67. Blood samples were assayed for P4 by RIA and for PSPB by ELISA, and expression of ISG15 was assessed in mRNA isolated from blood leukocytes on d 18 and 20. Data were analyzed by ANOVA and logistic regression using the MIXED and GLIMMIX procedures. In both experiments, treatment with hCG increased P4 concentrations from d 11 to 32; however, treatment did not affect P/AI or P/ET at d 32 or 67, PSPB concentrations from d 11 to 67 of pregnancy, or relative ISG15 mRNA concentrations on d 18 or 20. Heifers diagnosed not pregnant at d 32 in experiment 2 with an extended luteal phase (>20 d) and treated with hCG had greater relative ISG15 mRNA concentrations on d 20 than control heifers. Treatment with hCG did not affect pregnancy loss in experiment 1, whereas heifers treated with hCG at the time of IVF embryo transfer had fewer pregnancy losses from d 32 to 67 than control heifers. We concluded that treatment with 2,000 IU of hCG 7 d after AI or at the time of embryo transfer increased P4 concentrations without affecting P/AI or P/ET in nulliparous Holstein heifers.

Vitrification for bovine embryos with low-quality grade

This study was conducted to examine the utility of vitrification for bovine embryos with low-quality grade, and simple cryoprotectants dilution method for practitioners. In Experiment 1, survival of frozen embryos was compared with that of vitrified embryos using minimum volume cooling (MVC). Then, vitrified embryos were used to confirm the optimum sucrose concentration in Experiment 2. The survival rates of embryos that had been vitrified following diluted cryoprotectants with the one-step in-straw method were compared with those of fresh control embryos in Experiment 3. Frozen-thawed or vitrified-warmed blastocysts were cultured with TCM-199 supplemented with 100 μmol/L beta-mercaptoethanol +5% fetal bovine serum at 38.5°C in an atmosphere of 5% CO₂ in air, their survival after 24 hr were compared. The development to term of fair quality in vivo embryos after vitrification was examined in Experiment 4. Results show that survival rates of frozen-thawed embryos were lower (p < .05) than that of vitrified-warmed ones. When vitrified embryos were warmed in 0.3 mol/L sucrose in straws, their survival rate was 100%. The total cell numbers of vitrified-warmed embryos were comparable to those of fresh control embryos. The six calves from 13 vitrified embryos were delivered in Experiment 4. These results indicate that MVC vitrification following one-step cryoprotectants dilution is utilized to preserve low-quality bovine embryos.

Likelihood of pregnancy after the transfer of embryos derived from follicle aspiration and in vitro embryo production sessions with different relative efficiencies

The aim of the present study was to evaluate the likelihood of pregnancy of in vitro-produced (IVP) embryos from batches with distinct relative efficiencies. Data were retrospectively analyzed from 605 transvaginal ultrasonic-guided follicle aspiration sessions (OPU) followed by in vitro embryo production (IVEP) and 2456 fresh embryo transfers (ET), performed between 2008 and 2012 in individuals of the Gir (dairy Bos indicus) breed. The OPU and IVEP were performed using standard procedures by a single group of technicians at the same laboratory facility. Records were stratified into quartiles (I to IV) according to the total of cumulus-oocytes complexes (COC) produced per donor, or in percentile ranges (0%-25%, 26%-50%, 51%-75%, and 76%-100%) for endpoints related to COC quality or efficiency of embryo production. Pregnancy per embryo transfer (P/ET) was compared among quartiles or ranges using the chi-squared test. Donors producing a greater number of total COC (quartile I) also had more viable and grade I COC, and a greater number of embryos than donors ranked in quartiles II, III or IV, respectively (P < 0.0001). Nevertheless, P/ET did not differ (P > 0.05) among embryos produced by donors ranked in Quartiles I to IV. Similarly, there was no difference (P > 0.05) in P/ET for embryos derived from OPU sessions with a relatively greater or lesser percentage of viable or Grade I COC. Cleavage and blastocyst rates within each IVEP batch had no effect (P > 0.05) on P/ET. In conclusion, data suggest that there is no relationship among oocyte yield after OPU, or efficiency of IVEP, and the likelihood of pregnancy after ET of fresh IVP embryos.

Characteristics of candidate genes associated with embryonic development in the cow: Evidence for a role for WBP1 in development to the blastocyst stage

The goal was to gain understanding of how 12 genes containing SNP previously related to embryo competence to become a blastocyst (BRINP3, C1QB, HSPA1L, IRF9, MON1B, PARM1, PCCB, PMM2, SLC18A2, TBC1D24, TTLL3 and WBP1) participate in embryonic development. Gene expression was evaluated in matured oocytes and embryos. BRINP3 and C1QB were not detected at any stage. For most other genes, transcript abundance declined as the embryo developed to the blastocyst stage. Exceptions were for PARM1 and WBP1, where steady-state mRNA increased at the 9-16 cell stage. The SNP in WBP1 caused large differences in the predicted three-dimensional structure of the protein while the SNP in PARM1 caused smaller changes. The mutation in WBP1 causes an amino acid substitution located close to a P-P-X-Y motif involved in protein-protein interactions. Moreover, the observation that the reference allele varies between mammalian species indicates that the locus has not been conserved during mammalian evolution. Knockdown of mRNA for WBP1 decreased the percent of putative zygotes becoming blastocysts and reduced the number of trophectoderm cells and immunoreactive CDX2 in the resulting blastocysts. WBP1 is an important gene for embryonic development in the cow. Further research to identify how the SNP in WBP1 affects processes leading to differentiation of the embryo into TE and ICM lineages is warranted.

Fertility of Holstein heifers after two doses of PGF2α in 5-day CO-Synch progesterone-based synchronization protocol

The objective of the study was to determine the effect of three different PGF2α (PGF) treatments in the 5-day CO-Synch progesterone-based synchronization protocol on artificial insemination (AI) pregnancy rate (PR) in Holstein heifers in Turkey and the United States. We hypothesized that two doses of PGF administered concurrently or 6 hours apart would result in greater AI pregnancy compared with a single dose of PGF on Day 5 at controlled internal drug release (CIDR) removal. In Turkey, Holstein heifers (n = 450) from one farm in the province of Adana and another farm in the province of Bursa were included. In the US, Holstein heifers (n = 483) from two locations in the state of Idaho were included. Heifers within locations were randomly allocated to one of three protocol groups: 1PGF-received 25 mg IM of dinoprost at CIDR removal; 2Co-PGF-received 50 mg IM of dinoprost at CIDR removal, and 2PGF-received 25 mg IM of dinoprost at CIDR removal and an additional 25 mg IM of dinoprost 6 hours later. All heifers received a CIDR (1.38 g of progesterone) and GnRH (10 μg IM of Buserelin [Turkey] or gonadorelin hydrochloride [US]) on Day 0. The CIDRs were removed on Day 5, and each heifer was given PGF according to the assigned treatments. On Day 7, each heifer was given another dose of GnRH and concurrently inseminated at 56 hours after CIDR removal. Heifers in both experiments were examined for pregnancy status between 35 and 45 days after AI. Overall, controlling for age, the heifers in the 2PGF group had greater AI-PR (61.7% [192/311]) than heifers in 2Co-PGF (48.2% [149/309]; P < 0.001) or 1PGF (53.7% [168/313]; P < 0.05) groups. No difference was observed between 2Co-PGF and 1PGF groups (P > 0.1). In Turkey, the heifers in the 2PGF group had a greater AI-PR (60% [90/150]) than 2Co-PGF (45.3% (68/150); P < 0.01] group. No difference was observed between 2PGF and 1PGF (55.3% [83/150]) groups (P > 0.1). There was a trend for AI pregnancy between 1PGF and 2Co-PGF groups (P = 0.08). In the United States, the heifers in the 2PGF group had a greater AI-PR (63.4% [102/161]) than the heifers in 2PGF (50.9 [81/159]; P < 0.05) or 1PGF (52.1% [85/163]; P < 0.05) groups. Heifers that were 15- and 16-month old achieved greater AI-PR than 17- and 18-month-old heifers (59.2 [342/578] vs. 47.0% [168/355]; P < 0.01). In conclusion, administration of 2PGF at 6 hours apart on Day 5 at CIDR removal in a 5-day CO-Synch + CIDR protocol resulted in greater AI pregnancy. A greater number of 15- and 16-month-old heifers became pregnant compared with 17- and 18-month-old heifers.

Effects of parity and season on pregnancy rates after the transfer of embryos to repeat-breeder Japanese Black beef cattle

Abstract. Repeat-breeder (RB) cows are a major source of economic waste due to their decreased fertility. Embryo transfer (ET) is an alternative tool to improve the fertility of RB cows. The aims of the present study were to evaluate the effects of recipient parity and the season on pregnancy rates following ET in RB Japanese Black beef cattle. Embryos were transferred nonsurgically to recipients, consisting of 155 heifers (< 2 years old) and 172 cows (< 8 years old), which were defined as RB cattle. Of the recipients that were presented for ET, 57 recipients received a fresh embryo and 270 recipients received a frozen embryo. There were no differences in the pregnancy rates between cattle that received fresh embryos or frozen embryos. The rates of recipients with pregnancy, abortion, stillbirth, and normal calving were similar between heifers and cows. In cows, the pregnancy rates were lower (P < 0.05) in summer (June to August) than in spring (March to May) and winter (December to February). In heifers, however, there were no differences in the pregnancy rates among the seasons. Our findings indicate that in RB Japanese Black beef cattle, the parity of the recipients does not have an effect on the pregnancy rates following the transfer of fresh and frozen embryos. However, heat stress may affect reproductive performance in RB Japanese Black cows.

Preimplantation development of cloned canine embryos recovered by hysterectomy or surgical uterine flushing and subsequent pregnancy outcomes

Dog cloning offers a substantial potential because of the advancements in assisted reproductive technology and development of the human disease model in line with the transgenic technique. However, little is known about the development of the canine cloned embryo during the preimplantation period. The aim of this study was to investigate the most efficient method and time for collecting cloned canine preimplantation embryos and to ascertain the developmental timeline of cloned canine embryos. Two hundred cloned embryos were created and transferred into 11 surrogates. The preimplantation stage cloned embryos were then collected on Days 7, 8, and 9 using an ovariohysterectomy or the Foley balloon catheter method. The recovery rate of reconstructed embryos was 63.6% and 60.6% for the ovariohysterectomy and Foley balloon catheter methods, respectively. Although significant differences were observed in the early developmental stages (one-cell and 16-cell stages), no significant difference was observed in the blastocyst stage. Significantly higher blastocyst rate was observed when the embryos were collected on Day 8 (11.4%) than on Day 7 (0.0%; P < 0.05). At the proximal uterine horn on Day 7, no embryos at any stage were found, whereas on Days 8 and 9, blastocysts were found. We have observed a 63% initial pregnancy rate at 25 to 30 days after embryo transfer and a 50% full-term pregnancy rate, whereas 6.3% of the puppies were born, and 5.5% were born live among the total transferred embryos. Our results suggest that cloned embryos can develop to blastocysts by Day 8, and full-term pregnancy can be achieved after embryo transfer in canine.

Heat shock decreases the embryonic quality of frozen-thawed bovine blastocysts produced in vitro

In this study, the effect of heat shock on frozen-thawed blastocysts was evaluated using in vitro-produced (IVP) bovine embryos. In experiment 1, the effects of 6 h of heat shock at 41.0 C on fresh blastocysts were evaluated. HSPA1A expression as a reflection of stress was increased by heat shock (P < 0.05), but the expressions of the quality markers IFNT and POU5F1 were not affected. In experiment 2, frozen-thawed blastocysts were incubated at 38.5 C for 6 h (cryo-con) or exposed to heat shock at 41.0 C for 6 h (cryo-HS). Then, blastocysts were cultured at 38.5 C until 48 h after thawing (both conditions). Cryo-HS blastocysts exhibited a decreased recovery rate: HSPA1A expression was dramatically increased compared with that in fresh or cryo-con blastocysts at 6 h, and IFNT expression was decreased compared with that in cryo-con blastocysts at 6 h (both P < 0.05). Cryo-con blastocysts at 6 h also exhibited higher HSPA1A expression than fresh blastocysts (P < 0.05). At 48 h after thawing, the number of hatched blastocysts and blastocyst diameter were lower in cryo-HS blastocysts (P < 0.05). Cryo-con blastocysts showed lower POU5F1 levels at 48 h than fresh, cryo-con or cryo-HS blastocysts at 6 h (P < 0.05), but their POU5F1 levels were not different from those of cryo-HS blastocysts at 48 h. These results indicated that application of heat shock to frozen-thawed blastocysts was highly damaging. The increase in damage by the interaction of freezing-thawing and heat shock might be one reason for the low conception rate in frozen-thawed embryo transfer in summer.

Effects of acute feed restriction combined with targeted use of increasing luteinizing hormone content of follicle-stimulating hormone preparations on ovarian superstimulation, fertilization, and embryo quality in lactating dairy cows

Multiple metabolic and hormonal factors can affect the success of protocols for ovarian superstimulation. In this study, the effect of acute feed restriction and increased LH content in the superstimulatory FSH preparation on numbers of ovulations, fertilization, and embryo quality in lactating dairy cows was evaluated. Two experiments were performed using a Latin square design with treatments arranged as a 2 × 2 factorial: feed restriction (FR; 25% reduction in dry matter intake) compared with ad libitum (AL) feeding, combined with high (H) versus low (L) LH in the last 4 injections of the superstimulatory protocol. As expected, FR decreased circulating insulin concentrations (26.7 vs. 46.0 μU/mL). Two analyses were performed: one that evaluated the complete Latin square in experiment 2 and a second that evaluated only the first periods of experiments 1 and 2. For both analyses, follicle numbers, ovulation rates, and corpora lutea on d 7 were not different. In the first period analysis of experiments 1 and 2, we observed an interaction between feed allowance and amount of LH on fertilization rates, percentage of embryos or oocytes that were quality 1 and 2 embryos, and number of embryos or oocytes that were degenerate. Fertilization rates were greater for the AL-L (89.4%) and FR-H (80.1%) treatments compared with the AL-H (47.9%) and FR-L (59.9%) treatments. Similarly, the proportion of total embryos or oocytes designated as quality 1 and 2 embryos was greater for AL-L (76.7%) and FR-H (73.4%) treatments compared with AL-H (35.6%) and FR-L (47.3%) treatments. In addition, the number of degenerate embryos was decreased for AL-L (1.3) and FR-H (0.4) treatments compared with the AL-H (2.6) and FR-L (2.3) treatments. Thus, cows with either too low (FR-L) or too high (AL-H) insulin and LH stimulation had lesser embryo production after superstimulation because of reduced fertilization rate and increased percentage of degenerate embryos. Therefore, interaction of the gonadotropin content of the superstimulatory preparation with the nutritional program of the donor cow needs to be considered to optimize success of ovarian superstimulatory protocols.

Effects in cattle of genetic variation within the IGF1R gene on the superovulation performance and pregnancy rates after embryo transfer

The insulin-like growth factor 1 receptor (IGF1R) is a membrane glycoprotein mediating most biological actions of IGF1 and IGF2, and has an important effect on ovulation, pre-implantation embryo development and pregnancy rate. The objectives of this study were to detect IGF1R gene polymorphisms of cattle and analyze the relationship with superovulation performance and pregnancy rates after embryo transfer (ET), as well as the hormone concentrations at the day of ET. One reported SNP of IGF1R G404T and a novel SNP of IGF1R G399A were analyzed in 170 Chinese Holstein donor cows and 118 Luxi recipients cattle. Statistical analysis revealed that the G404T mutation was associated (p=0.019) with increased ovulation rate and females with this mutation had enhanced performance in producing transferable embryos. For the polymorphic locus G399A, recipients with g.399 GG and g.399 GA genotypes had greater pregnancy rates after ET than that of g.399 AA genotype. Furthermore, the same tendency was observed that the genotype groups with greater pregnancy rates had greater progesterone and lesser estrogen concentrations, but these did not reach statistical significance. Results of the present study showed, for the first time, that the polymorphism in IGF1R is associated with superovulation traits, and indicated that the IGFIR gene can be used as a potential marker for donor selection.

Assessment of the viability of embryos stored in liquid nitrogen produced commercially using culture medium as a complementary test for stereoscopic microscopy

Summary The objective of the present study was to evaluate the viability of frozen embryos obtained from various private farmers in a culture medium for 4 h. Forty-seven embryos were used that had been previously graded as good and fair. These embryos were evaluated using stereoscopic microscopy by experienced clinicians prior to freezing. Embryos were divided in two groups: the non-cultured group, made up of six good quality embryos, and five fair; and the cultured group that consisted of 20 good quality embryos and 16 fair. Fifty-four per cent of the good quality embryos achieved a favourable development during culture whereas just 42% of embryos determined to be fair were observed to have adequate development. This evaluation was undertaken by serial photographs obtained at the onset of culture and 4 h later. This finding was corroborated by a more specific technique: terminal deoxynucleotide transferase dUTP nick end labelling-bromodeoxyuridine (TUNEL-BrdU). These results are indicative of the necessity of tight quality controls for commercially produced frozen embryos, as once thawed it is unlikely that clinicians will examine them to determine their physiological status prior to transfer.

Factors affecting fertilisation and early embryo quality in single- and superovulated dairy cattle

Data on fertilisation and embryo quality in dairy cattle are presented and the main factors responsible for the low fertility of single-ovulating lactating cows and embryo yield in superovulated dairy cattle are highlighted. During the past 50 years, the fertility in high-producing lactating dairy cattle has decreased as milk production increased. Recent data show conception rates to first service to be approximately 32% in lactating cows, whereas in heifers it has remained above 50%. Fertilisation does not seem to be the principal factor responsible for the low fertility in single-ovulating cows, because it has remained above 80%. Conversely, early embryonic development is impaired in high-producing dairy cows, as observed by most embryonic losses occurring during the first week after fertilisation. However, in superovulated dairy cattle, although fertilisation failure is more pronounced, averaging approximately 45%, the percentage of fertilised embryos viable at 1 week is quite high (>70%). Among the multifactorial causes of low fertility in lactating dairy cows, high feed intake associated with low concentrations of circulating steroids may contribute substantially to reduced embryo quality. Fertilisation failure in superovulated cattle may be a consequence of inappropriate gamete transport due to hormonal imbalances.

Effect of fixed-time embryo transfer on reproductive efficiency in high-producing repeat-breeder Holstein cows

The aim of the present study was to compare a synchronization of time of ovulation protocol for fixed-timed embryo transfer (FTET) with the usual administration of a single dose of prostaglandin associated with detection of estrus. Also, the effect of the presence of CL at the beginning of FTET protocol was evaluated. Lactating Holstein cows (n=651) with three previous artificial inseminations were classified according to presence or absence of a corpus luteum (CL). Cows with a CL were randomly assigned to two additional treatments and submitted to embryo transfer after detection of estrus (PGF-Estrus) or FTET (FTET-CL). Cows without CL were allocated to the FTET-NoCL treatment. On a random day of the estrous cycle (Day 0), cows in the PGF-Estrus treatment (n=229) were treated with 150 microg d-cloprostenol (PGF) i.m. followed by detection of estrus from Day 1 through Day 5 after PGF. Embryos were transferred 6-8 days after estrus detection. Cows in the FTET-CL (n=208; presence of CL) and FTET-NoCL (n=214; absence of CL) treatments received a norgestomet ear implant plus 2mg estradiol benzoate (EB) and 50mg progesterone i.m. on Day 0. On Day 8, the implant was removed and 400 IUeCG, 150 microg d-cloprostenol and 1mg estradiol cypionate i.m. were administered. No detection of estrus was performed and Day 10 was arbitrarily considered as the estrus day. Ultrasonographic exams were performed in all recipients and only cows with a single CL> or =15 mm or multiple CL received a fresh or frozen-thawed embryo on Day 17. Pregnancy was diagnosed by ultrasonography at 30 and 60 days of pregnancy. When FTET and PGF-Estrus were compared, the proportion of cows receiving an embryo (recipients transferred-to-treated rate) was greater in the FTET-CL (75.0% (156/208) than in PGF-Estrus (34.5%, 79/229; P<0.0001) treatment. Pregnancy rate (60 days) was also greater in FTET-CL (29.3%, 61/208) when compared to PGF-Estrus (16.2%, 37/229; P=0.001). However, no differences were found in pregnancy loss [PGF-Estrus=11.9% (5/42), FTET-CL=9.0% (6/67); P=0.62] and circulating progesterone concentration at embryo transfer [PGF-Estrus=4.02+/-0.52 ng/mL (n=25), FTET-CL=3.33+/-0.32 ng/mL (n=27); P=0.25] among these treatments. The presence of CL at the beginning of FTET protocol resulted greater transferred-to-treated rate [FTET-CL=75.0% (156/208) vs. FTET-NoCL=61.2% (131/214); P=0.003], but showed no effect on pregnancy rate at 60 days [FTET-CL=29.3% (61/208) vs. FTET-NoCL=22.9% (49/214); P=0.13], pregnancy loss [FTET-CL=9.0% (6/67) vs. FTET-NoCL=2.0% (1/50); P=0.15] and circulating progesterone concentration at ET [FTET-CL=3.33+/-0.32 ng/mL (n=27) compared to FTET-NoCL=3.44+/-0.40 ng/mL (n=2 9); P=0.82]. In conclusion, the protocol for synchronization of time of ovulation using norgestomet ear implant, EB and eCG increased recipients transferred-to-treated and pregnancy rates in high-producing repeat-breeder Holstein cows. Also, recipients without CL at the beginning of the time of ovulation synchronization treatment resulted in similar pregnancy rate as recipients with CL submitted to FTET protocol. Thus, the suggested protocol allowed the performance of FTET, without the need for detection of estrus, simplifying the reproductive management and increasing the reproductive efficiency in repeat-breeder Holstein recipients.