Vitrification of immature and matured bovine oocytes: effect of brilliant cresyl blue selection and hyaluronan addition

The aim of the present study was to evaluate the effect of brilliant cresyl blue (BCB) selection, the type of oocyte (immature or matured) and the use of hyaluronan in the vitrification solution on further embryo developmental competence. Oocytes (n = 1308) obtained from abattoir ovaries were classified by BCB stain. Control oocytes were maintained in holding media for 90 min and then subdivided to be placed into maturation media without any treatment or were vitrified. Immature or matured oocytes were vitrified by the solid-surface technique using two different vitrification solutions. VS1: composed of 10% ethylene glycol (EG) for 10 min followed by 20% EG + 0.2M trehalose for 30 sec and finally into 30% EG + 0.5M trehalose for 30 sec, or VS2 composed by 10% EG for 10 min, followed by 20% EG + 0.2M trehalose for 30 sec, and finally into 30% EG+ 0.5M trehalose + 0.1 g/ml hyaluronan for 30 sec. Oocytes were then loaded into Fyberplugs™ and vitrified. After one week, Fyberplugs™ were open and placed directly into (37°C) 0.5M sucrose solution for 5 min, then into 0.25M of sucrose for another 5 min and finally placed into maturation medium for in vitro production. Cleavage and development rates were examined on days 2 and 7 after fertilization, respectively. The blastocyst rate of vitrified oocytes selected as BCB + (5.5 ± 0.6%) were higher than those selected as BCB - (1.0 ± 0.4%) and those that were not selected by BCB (2.0 ± 1.1%; P < 0.001). Furthermore, immature vitrified oocytes had greater (P < 0.05) cleavage and blastocyst rates (44.8 ± 1.9% and 4.0 ± 0.6%) than matured vitrified oocytes (38.3 ± 2.8% and 2.5 ± 0.6%). Finally, the addition of hyaluronan to the vitrification solution had no significant effect on development rates. In conclusion, the selection of oocytes by BCB and the use of immature oocytes increase the development rates of vitrified-warmed oocytes.

Vitrification of immature and matured bovine oocytes: effect of brilliant cresyl blue selection and hyaluronan addition

The aim of the present study was to evaluate the effect of brilliant cresyl blue (BCB) selection, the type of oocyte (immature or matured) and the use of hyaluronan in the vitrification solution on further embryo developmental competence. Oocytes (n = 1308) obtained from abattoir ovaries were classified by BCB stain. Control oocytes were maintained in holding media for 90 min and then subdivided to be placed into maturation media without any treatment or were vitrified. Immature or matured oocytes were vitrified by the solid-surface technique using two different vitrification solutions. VS1: composed of 10% ethylene glycol (EG) for 10 min followed by 20% EG + 0.2M trehalose for 30 sec and finally into 30% EG + 0.5M trehalose for 30 sec, or VS2 composed by 10% EG for 10 min, followed by 20% EG + 0.2M trehalose for 30 sec, and finally into 30% EG+ 0.5M trehalose + 0.1 g/ml hyaluronan for 30 sec. Oocytes were then loaded into Fyberplugs™ and vitrified. After one week, Fyberplugs™ were open and placed directly into (37°C) 0.5M sucrose solution for 5 min, then into 0.25M of sucrose for another 5 min and finally placed into maturation medium for in vitro production. Cleavage and development rates were examined on days 2 and 7 after fertilization, respectively. The blastocyst rate of vitrified oocytes selected as BCB + (5.5 ± 0.6%) were higher than those selected as BCB - (1.0 ± 0.4%) and those that were not selected by BCB (2.0 ± 1.1%; P < 0.001). Furthermore, immature vitrified oocytes had greater (P < 0.05) cleavage and blastocyst rates (44.8 ± 1.9% and 4.0 ± 0.6%) than matured vitrified oocytes (38.3 ± 2.8% and 2.5 ± 0.6%). Finally, the addition of hyaluronan to the vitrification solution had no significant effect on development rates. In conclusion, the selection of oocytes by BCB and the use of immature oocytes increase the development rates of vitrified-warmed oocytes.(AU)

Effect of follicle wave synchronization and gonadotropin treatments on the number and quality of cumulus-oocyte complex obtained by ultrasound-guided ovum pick-up in beef cattle

Four experiments were designed to evaluate the effect of different hormonal treatments on the number and quality of cumulus oocyte complexes (COCs) recovered by ovum pick-up (OPU) in beef cattle. Experiment 1 compared the synchronization of follicle wave emergence with 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4) given intramuscularly (i.m.) 6 days before OPU versus a control group in which donors did not receive any treatment. Experiment 2 evaluated the use of equine chorionic gonadotropin (eCG) and prostaglandin F2α prior to OPU. Experiment 3 compared the effect of dominant follicle removal (DFR) by ultrasound guided follicle aspiration or EB+P4 to control follicular wave emergence, and treatment with eCG or FSH to superstimulate follicle growth. Experiment 4 evaluated the effect of inserting a progesterone releasing device (CIDR) during the superstimulation treatment. In experiment 1, treatment with EB+P4 resulted in more (P < 0.05) viable COCs (5.2 ± 0.9 vs. 2.1 ± 0.4) than the controls. In experiment 2, prostaglandin F2α prior to OPU increased (P < 0.05) the number of viable COCs (7.9 ± 1.1), but treatment with eCG did not affect (P > 0.1) the number of COCs (4.5 ± 1.0) recovered compared to the controls (4.7± 0.7). In experiment 3, there were no differences (P > 0.1) between DFR and EB+P4; however, treatment with FSH resulted in more (P < 0.05) COCs recovered than eCG (6.8 ± 0.6 vs. 3.7 ± 0.6). In experiment 4, insertion of a CIDR device did not affect the number of COCsrecovered compared to the controls (6.3 ± 0.7 vs. 5.8 ± 0.7,respectively). In conclusion, the use of treatments that synchronize follicle wave emergence, prostaglandin F2a to avoid the presence CL at the time of OPU and superstimulation with FSH were useful to improve the number of COCs recovered in beef cattle. Conversely, the insertion of a CIDR device during the superstimulation treatment prior to OPU did not improve the number of COCs recovered nor their quality.(AU)

Effect of follicle wave synchronization and gonadotropin treatments on the number and quality of cumulus-oocyte complex obtained by ultrasound-guided ovum pick-up in beef cattle

Four experiments were designed to evaluate the effect of different hormonal treatments on the number and quality of cumulus oocyte complexes (COCs) recovered by ovum pick-up (OPU) in beef cattle. Experiment 1 compared the synchronization of follicle wave emergence with 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4) given intramuscularly (i.m.) 6 days before OPU versus a control group in which donors did not receive any treatment. Experiment 2 evaluated the use of equine chorionic gonadotropin (eCG) and prostaglandin F2α prior to OPU. Experiment 3 compared the effect of dominant follicle removal (DFR) by ultrasound guided follicle aspiration or EB+P4 to control follicular wave emergence, and treatment with eCG or FSH to superstimulate follicle growth. Experiment 4 evaluated the effect of inserting a progesterone releasing device (CIDR) during the superstimulation treatment. In experiment 1, treatment with EB+P4 resulted in more (P 0.1) the number of COCs (4.5 ± 1.0) recovered compared to the controls (4.7± 0.7). In experiment 3, there were no differences (P > 0.1) between DFR and EB+P4; however, treatment with FSH resulted in more (P < 0.05) COCs recovered than eCG (6.8 ± 0.6 vs. 3.7 ± 0.6). In experiment 4, insertion of a CIDR device did not affect the number of COCsrecovered compared to the controls (6.3 ± 0.7 vs. 5.8 ± 0.7,respectively). In conclusion, the use of treatments that synchronize follicle wave emergence, prostaglandin F2a to avoid the presence CL at the time of OPU and superstimulation with FSH were useful to improve the number of COCs recovered in beef cattle. Conversely, the insertion of a CIDR device during the superstimulation treatment prior to OPU did not improve the number of COCs recovered nor their quality.

Updates on embryo production strategies

The embryo production technologies are used to enhance genetic progress through female and male lineages. Advances in the control of ovarian follicular wave emergence, superstimulation and ovulation with self-appointed treatments have facilitated donor and recipient management. However, these procedures can be influenced by several factors related to the animals and their management. Therefore, researchers continue to investigate the ideal reproductive environments and treatments to maintain the viability of the techniques and field applicability.(AU)

Updates on embryo production strategies

The embryo production technologies are used to enhance genetic progress through female and male lineages. Advances in the control of ovarian follicular wave emergence, superstimulation and ovulation with self-appointed treatments have facilitated donor and recipient management. However, these procedures can be influenced by several factors related to the animals and their management. Therefore, researchers continue to investigate the ideal reproductive environments and treatments to maintain the viability of the techniques and field applicability.

Innovative strategies for superovulation in cattle

Although superstimulatory protocols in cattle are usually initiated during mid-cycle, the elective control follicular wave emergence and ovulation have had a great impact on the application of on-farm embryo transfer. However, the most commonly used approach for the sinchronization of follicular wave emergence invoolves the use of estradiol which cannot be used in many parts of the world. Therefore, the need for alternative treatments has driven recent research. An approach that has shown promise is to initiate FSH treatments at the time of the emergence of the first follicular wave folliwing GnRH-induced ovulation. Alternatively, it has been shown that that it may be possible to ignore follicular wave status, and by extending the treatment protocol induce smaller follicles to grow and reach maturity and superovulate. Finally , the short half-life of pintuitary FSH necessitates twice daily treatments which are times consuming, stressful and subject to error. Recent treatment protocols have permitted supertimulation with a single or alternatively two-FSH treatments, reducing the need for animal handling during FSH treatments.

Evaluation and classification of bovine embryos

Bovine Embryo transfer has been used widely to reproduce the most valuable females in the herd with about 750,000 embryos produced annually from superovulated donors and more than 450,000 embryos produced are the safest and most cost affective alternatives to move genetics internationally because og their low risk of transmitting diseases. One of most important factors associated with the success and widepread application of this technologie is evaluation of the embryos before freezing and/or transfer to a recipient. Embryos are usually classified based on a number code system for their stage of development (1 to 9) and for their quality (1 to 4). The basic principles of embryo evaluation are briefly described.

Evaluation and classification of bovine embryos

Bovine Embryo transfer has been used widely to reproduce the most valuable females in the herd with about 750,000 embryos produced annually from superovulated donors and more than 450,000 embryos produced are the safest and most cost affective alternatives to move genetics internationally because og their low risk of transmitting diseases. One of most important factors associated with the success and widepread application of this technologie is evaluation of the embryos before freezing and/or transfer to a recipient. Embryos are usually classified based on a number code system for their stage of development (1 to 9) and for their quality (1 to 4). The basic principles of embryo evaluation are briefly described.(AU)

Innovative strategies for superovulation in cattle

Although superstimulatory protocols in cattle are usually initiated during mid-cycle, the elective control follicular wave emergence and ovulation have had a great impact on the application of on-farm embryo transfer. However, the most commonly used approach for the sinchronization of follicular wave emergence invoolves the use of estradiol which cannot be used in many parts of the world. Therefore, the need for alternative treatments has driven recent research. An approach that has shown promise is to initiate FSH treatments at the time of the emergence of the first follicular wave folliwing GnRH-induced ovulation. Alternatively, it has been shown that that it may be possible to ignore follicular wave status, and by extending the treatment protocol induce smaller follicles to grow and reach maturity and superovulate. Finally , the short half-life of pintuitary FSH necessitates twice daily treatments which are times consuming, stressful and subject to error. Recent treatment protocols have permitted supertimulation with a single or alternatively two-FSH treatments, reducing the need for animal handling during FSH treatments.(AU)

Increasing pregnancies following synchronization of bovine recipients

The success of a commercial embryo transfer program depends on the production of high numbers of viable embryos from donor cows that result in high numbers of calves born when the embryos are transferred to suitable recipien ts. In recent years, a great deal of effort has been devoted to the development of treatment protocols that permit the efficient use of recipients and result in high pregnancy per recipient synchronized, especially in recipients managed on pasture. One of the most successful alternatives to increase the number of recipients utilized in embryo transfer programs is the use of protocols that allow for embryo transfer without the need for estrus detection, usually called fixed-time embryo transfer (FTET). Pregnancies to FTET have been reported to be similar to those after detection of estrus, but the overall proportion of recipients pregnant over those synchronized are higher because these treatments have increased the proportion of recipients that receive embryos. Treatments that increase pr ogesterone concentrations and pregnancies per embryo transfer have also been investigated in recent years. Most of these treatments have resulted in increased pregnancy per embryo transfer in recipients with Bos indicus influence, while benefit were not so obvious in Bos taurus recipients managed under more optimal conditions. While factors such as the reproductive histor y of the recipients and the stage and quality of embryos may affect pregnancy per embryo transfer, other factors such as estrus detection and the time interval from thawing to transfer do not seem to affect the proportion of recipients pregnant with embryos frozen in ethylene glycol and transferred at a fixed-time.

Increasing pregnancies following synchronization of bovine recipients

The success of a commercial embryo transfer program depends on the production of high numbers of viable embryos from donor cows that result in high numbers of calves born when the embryos are transferred to suitable recipien ts. In recent years, a great deal of effort has been devoted to the development of treatment protocols that permit the efficient use of recipients and result in high pregnancy per recipient synchronized, especially in recipients managed on pasture. One of the most successful alternatives to increase the number of recipients utilized in embryo transfer programs is the use of protocols that allow for embryo transfer without the need for estrus detection, usually called fixed-time embryo transfer (FTET). Pregnancies to FTET have been reported to be similar to those after detection of estrus, but the overall proportion of recipients pregnant over those synchronized are higher because these treatments have increased the proportion of recipients that receive embryos. Treatments that increase pr ogesterone concentrations and pregnancies per embryo transfer have also been investigated in recent years. Most of these treatments have resulted in increased pregnancy per embryo transfer in recipients with Bos indicus influence, while benefit were not so obvious in Bos taurus recipients managed under more optimal conditions. While factors such as the reproductive histor y of the recipients and the stage and quality of embryos may affect pregnancy per embryo transfer, other factors such as estrus detection and the time interval from thawing to transfer do not seem to affect the proportion of recipients pregnant with embryos frozen in ethylene glycol and transferred at a fixed-time.(AU)

Developmental rates of in vivo and in vitro produced bovine embryos cryopreserved in ethylene glycol based solutions by slow freezing or solid surface vitrification

The aim of this study was to compare in vitro survival rates of in vivo and in vitro -produced bovine embryos by slow freezing or solid surface v itrification. In vivo -produced blastocysts (n = 210) and in vitro - produced blastocysts (n = 445) were randomly allocated in two cryopreservation groups. Group 1 - embryos were exposed to 1.5 M ethylene glycol (EG) for 5 min, loaded in 0.5 ml straws, frozen at -6.5ºC and seeded. After 10 min of equilibration, straws were cooled at -0.6ºC/min until - 35ºC, and then plunged into liquid nitrogen (-196ºC). Group 2 - embryos were exposed to a 15% EG + 0.25 M trehalose solution for 1 min and then a 30% EG + 1 M trehalose solution for 30 sec to be vitrified using the Cryologic Vitrification Method (CVM ® ). After at least one week of storage, embryos in the slow freezing group were thawed in a wate r bath at 30°C for 12 sec and then placed in holding medium for 5 min and transferred into SOF culture media. Vitrified embryos were placed directly into a 0.25 M sucrose solution for 5 min then cultured in SOF medium. Re-expansion and hatching rates were evaluated at 24 and 72 h, respectively. In vivo -produced embryos had higher (P < 0.01) re-expansion (179/210, 81% vs . 244/445, 54%) and hatching rates (159/210, 72% vs . 177/445, 39%) than in vitro -produced embryos, regardless of the cryopreservation method. However, re-expansion and hatching rates were higher (P < 0.01) for in vitro -produced vitrified embryos (155/223, 69% and 132/223, 59%) than in vitro -produced embryos cryopreserved by slow freezing (89/222, 40% a nd 45/222, 20%). Although similar re-expansion rates were obtained with in vivo - produced embryos cryopreserved by the two systems, hatching rates tended to be lower (P = 0.09) with in vivo -produced embryos that were vitrified as compared to slow freezing. In conclusion, solid surface vitrification improved the cryosurvival rates of in vitro - produced embryos compared to the conventional slow freezing procedure.

Developmental rates of in vivo and in vitro produced bovine embryos cryopreserved in ethylene glycol based solutions by slow freezing or solid surface vitrification

The aim of this study was to compare in vitro survival rates of in vivo and in vitro -produced bovine embryos by slow freezing or solid surface v itrification. In vivo -produced blastocysts (n = 210) and in vitro - produced blastocysts (n = 445) were randomly allocated in two cryopreservation groups. Group 1 - embryos were exposed to 1.5 M ethylene glycol (EG) for 5 min, loaded in 0.5 ml straws, frozen at -6.5ºC and seeded. After 10 min of equilibration, straws were cooled at -0.6ºC/min until - 35ºC, and then plunged into liquid nitrogen (-196ºC). Group 2 - embryos were exposed to a 15% EG + 0.25 M trehalose solution for 1 min and then a 30% EG + 1 M trehalose solution for 30 sec to be vitrified using the Cryologic Vitrification Method (CVM ® ). After at least one week of storage, embryos in the slow freezing group were thawed in a wate r bath at 30°C for 12 sec and then placed in holding medium for 5 min and transferred into SOF culture media. Vitrified embryos were placed directly into a 0.25 M sucrose solution for 5 min then cultured in SOF medium. Re-expansion and hatching rates were evaluated at 24 and 72 h, respectively. In vivo -produced embryos had higher (P < 0.01) re-expansion (179/210, 81% vs . 244/445, 54%) and hatching rates (159/210, 72% vs . 177/445, 39%) than in vitro -produced embryos, regardless of the cryopreservation method. However, re-expansion and hatching rates were higher (P < 0.01) for in vitro -produced vitrified embryos (155/223, 69% and 132/223, 59%) than in vitro -produced embryos cryopreserved by slow freezing (89/222, 40% a nd 45/222, 20%). Although similar re-expansion rates were obtained with in vivo - produced embryos cryopreserved by the two systems, hatching rates tended to be lower (P = 0.09) with in vivo -produced embryos that were vitrified as compared to slow freezing. In conclusion, solid surface vitrification improved the cryosurvival rates of in vitro - produced embryos compared to the conventional slow freezing procedure.(AU)

Follicular dynamics and pregnancy rates in Bos taurus x Bos indicus embryo transfer recipients treated to increase plas ma progesterone concentrations

The aim of this study was to evaluate the effects of GnRH, LH, hCG or exogenous progesterone administration on plasma progesterone concentrations and pregnancy rates following embryo transfer in Bos taurus x Bos indicus cross-bred heifers. In Experiment 1, animals with body condition scores  3.5 (1 to 5 scale) were synchronized with two injections of a prostaglandin F2  analog 13 days apart. He ifers detected in estrus (day 0; n = 37) were randomly assigned on day 7 to receive one of five treatments: Control (2 ml saline im; n = 6), GnRH (10  g Buserelin im; n = 8), hCG (1500 IU Chorulon im; n = 8), LH (25 mg pLH im; n = 7) or a CIDR-B device for 13 days (n = 8). Ovarian ultrasonography was performed daily from day 6 until the subsequent estrus. Heifers in the GnRH, hCG and LH groups were evaluated every 12 h between days 7 and 9 to confirm ovulation of the first-wave dominant follicle. Blood samples were collected daily for determination of P4 levels. Estrus detection was performed daily with the aid of androgenized cows. Ovulation rate for the first wave dominant follicle was 100% for heifers treated with GnRH, hCG and LH. Between days 13 and 17, the mean diameter of original CLs, diameter of accessory CLs and P4 concentrations were greater in heifers treated with hCG than in heifers in all other groups (P < 0.05). Duration of the luteal phase (number of days with a P4 concentration  1.0 ng/ml) was similar in hCG (14.3 ± 0.6), LH (13.4 ± 0.6), GnRH (13.4 ± 0.4), CIDR-B (14.5 ± 0.2) and Control (12.8 ± 0.5) groups. In Experiment 2, animals were kept on a grazing regimen at commercial farms in Brazil and were synchronized with one injection of a prostaglandin F2  analog. The same hormonal treatments as in Experiment 1 were given on day 7 after estrus at the time of transfer of frozen/thawed embryos to Bos taurus x Bos indicus recipients (n = 485). Pregnancy rates were higher in GnRH- (53.5%; 53/99) and hCG- (51.0%; 49/96) treated heifers (P < 0.05) than in control heifers (28.6%; 28/98), but were similar to heifers treated with CIDR devices (41.1%; 39/95) and LH (45.4%; 44/97). It was concluded that the improvement in conception rates in hCG treated Bos taurus x Bos indicus cross-bred heifers receiving frozen/thawed embryos were due to both P4-dependent and P4-independent mechanisms.

Follicular dynamics and pregnancy rates in Bos taurus x Bos indicus embryo transfer recipients treated to increase plas ma progesterone concentrations

The aim of this study was to evaluate the effects of GnRH, LH, hCG or exogenous progesterone administration on plasma progesterone concentrations and pregnancy rates following embryo transfer in Bos taurus x Bos indicus cross-bred heifers. In Experiment 1, animals with body condition scores  3.5 (1 to 5 scale) were synchronized with two injections of a prostaglandin F2  analog 13 days apart. He ifers detected in estrus (day 0; n = 37) were randomly assigned on day 7 to receive one of five treatments: Control (2 ml saline im; n = 6), GnRH (10  g Buserelin im; n = 8), hCG (1500 IU Chorulon im; n = 8), LH (25 mg pLH im; n = 7) or a CIDR-B device for 13 days (n = 8). Ovarian ultrasonography was performed daily from day 6 until the subsequent estrus. Heifers in the GnRH, hCG and LH groups were evaluated every 12 h between days 7 and 9 to confirm ovulation of the first-wave dominant follicle. Blood samples were collected daily for determination of P4 levels. Estrus detection was performed daily with the aid of androgenized cows. Ovulation rate for the first wave dominant follicle was 100% for heifers treated with GnRH, hCG and LH. Between days 13 and 17, the mean diameter of original CLs, diameter of accessory CLs and P4 concentrations were greater in heifers treated with hCG than in heifers in all other groups (P < 0.05). Duration of the luteal phase (number of days with a P4 concentration  1.0 ng/ml) was similar in hCG (14.3 ± 0.6), LH (13.4 ± 0.6), GnRH (13.4 ± 0.4), CIDR-B (14.5 ± 0.2) and Control (12.8 ± 0.5) groups. In Experiment 2, animals were kept on a grazing regimen at commercial farms in Brazil and were synchronized with one injection of a prostaglandin F2  analog. The same hormonal treatments as in Experiment 1 were given on day 7 after estrus at the time of transfer of frozen/thawed embryos to Bos taurus x Bos indicus recipients (n = 485). Pregnancy rates were higher in GnRH- (53.5%; 53/99) and hCG- (51.0%; 49/96) treated heifers (P < 0.05) than in control heifers (28.6%; 28/98), but were similar to heifers treated with CIDR devices (41.1%; 39/95) and LH (45.4%; 44/97). It was concluded that the improvement in conception rates in hCG treated Bos taurus x Bos indicus cross-bred heifers receiving frozen/thawed embryos were due to both P4-dependent and P4-independent mechanisms.(AU)

Follicular growth and plasma progesterone patterns in Bos indicus x Bos taurus heifers submitted to different PGF2/progesterone-based synchronization protocols

The effect of different levels of progesterone (P4) concentrations on follicle growth and ovulatory capacity was evaluated in 40 crossbred Bos indicus x Bos taurus cyclic heifers submitted to distinct PGF2α + progesterone-based protocols. Heifers in CIDR_PGF8 group (n = 10) received 2.0 mg i.m. estradiol benzoate (EB) and a new controlled internal drug release containing 1.9 g of progesterone (CIDR) on day 0 of study. At the time of CIDR withdrawal (day 8), heifers received an i.m. injection of PGF2α and 24 h later a second EB i.m. injection (0.5 mg). The three other groups received EB injections and CIDR insertion/withdrawal as aforementioned, except that an i.m. injection of PGF2α was administered on day 5. In addition, heifers in the CIDR_PGF5 group (n = 10) received a new CIDR, while heifers in theCIDR1x_PGF5 (n = 9) and CIDR2x_PGF5 (n = 11) groups received a previously used CIDR for 8 and 14 days, respectively. Heifers that received a PGF2α injection on day 5 showed lower circulating P4 than heifers treated on day 8 (CIDR_PGF5 = 1.98 ± 0.21 ng/ml; CIDR1x_PGF5 = 1.69 ± 0.17 ng/ml and CIDR2x_PGF5 = 1.33 ± 0.08 ng/ml versus CIDR_PGF8 = 3.31 ± 0.45 ng/ml). The dominant follicle (DF) growth rate was slower in those heifers receiving PGF2α injection on day 8 (CIDR_PGF8 = 0.72 ± 0.13 mm/day) than groups treated on day 5 (CIDR_PGF5 = 0.96 ± 0.12 mm/day; CIDR1x_PGF5 = 1.06 ± 0.15 mm/day and CIDR2x_PGF5 = 1.01 ± 0.06mm/day). In consequence, preovulatory follicle diameter on day 10 was smaller in those animals injected on day 8 (CIDR_PGF8 = 8.81 ± 6.7 mm) than in those treated on day 5 (CIDR_PGF5 = 10.00 ± 0.58 mm CIDR1x_PGF5 = 10.5 ± 0.69 mm and CIDR2x_PGF5 = 10.5 ± 0.35 mm). For heifers receiving PGF2α injection on day 5, no significant differences on plasma P4 concentrations, folliculargrowth rate and DF diameters were observed among heifers that received new or previously used CIDR inserts. These results suggest that the presence of corpus luteum during synchronization protocols is the main factor responsible for the increase in the plasma P4 concentrations and inhibition of DF growth.(AU)

Follicular growth and plasma progesterone patterns in Bos indicus x Bos taurus heifers submitted to different PGF2/progesterone-based synchronization protocols

The effect of different levels of progesterone (P4) concentrations on follicle growth and ovulatory capacity was evaluated in 40 crossbred Bos indicus x Bos taurus cyclic heifers submitted to distinct PGF2α + progesterone-based protocols. Heifers in CIDR_PGF8 group (n = 10) received 2.0 mg i.m. estradiol benzoate (EB) and a new controlled internal drug release containing 1.9 g of progesterone (CIDR) on day 0 of study. At the time of CIDR withdrawal (day 8), heifers received an i.m. injection of PGF2α and 24 h later a second EB i.m. injection (0.5 mg). The three other groups received EB injections and CIDR insertion/withdrawal as aforementioned, except that an i.m. injection of PGF2α was administered on day 5. In addition, heifers in the CIDR_PGF5 group (n = 10) received a new CIDR, while heifers in theCIDR1x_PGF5 (n = 9) and CIDR2x_PGF5 (n = 11) groups received a previously used CIDR for 8 and 14 days, respectively. Heifers that received a PGF2α injection on day 5 showed lower circulating P4 than heifers treated on day 8 (CIDR_PGF5 = 1.98 ± 0.21 ng/ml; CIDR1x_PGF5 = 1.69 ± 0.17 ng/ml and CIDR2x_PGF5 = 1.33 ± 0.08 ng/ml versus CIDR_PGF8 = 3.31 ± 0.45 ng/ml). The dominant follicle (DF) growth rate was slower in those heifers receiving PGF2α injection on day 8 (CIDR_PGF8 = 0.72 ± 0.13 mm/day) than groups treated on day 5 (CIDR_PGF5 = 0.96 ± 0.12 mm/day; CIDR1x_PGF5 = 1.06 ± 0.15 mm/day and CIDR2x_PGF5 = 1.01 ± 0.06mm/day). In consequence, preovulatory follicle diameter on day 10 was smaller in those animals injected on day 8 (CIDR_PGF8 = 8.81 ± 6.7 mm) than in those treated on day 5 (CIDR_PGF5 = 10.00 ± 0.58 mm CIDR1x_PGF5 = 10.5 ± 0.69 mm and CIDR2x_PGF5 = 10.5 ± 0.35 mm). For heifers receiving PGF2α injection on day 5, no significant differences on plasma P4 concentrations, folliculargrowth rate and DF diameters were observed among heifers that received new or previously used CIDR inserts. These results suggest that the presence of corpus luteum during synchronization protocols is the main factor responsible for the increase in the plasma P4 concentrations and inhibition of DF growth.

Control of ovarian function for assisted reproductive technologies in cattle

Although the discovery that follicles in bovine ovaries grow in a wave-like fashion has presented challenges for estrus synchronization and superovulation, recent protocols, designed to control follicular function have permitted fixed-time AI or fixed-time embryo transfer with high pregnancy rates, and the initiation of superstimulatory treatments at a self-appointed time, all without the necessity of estrus detection. The key is the synchronization of follicle wave emergence. More recent studies have revealed that it is not only possible to synchronize the timing of ovulation for fixed-time AI in single ovulating animals, but also in superstimulated donors. Ultrasound-guided follicle ablation is very efficacious in synchronizing follicle wave emergence but is difficult to apply in the field. Similarly, the induction of ovulation with GnRH or LH will effectively synchronize follicle wave emergence, but ovulation occurs in only 60 to 70% of cases. The administration of estradiol benzoate in progestin-treated cattle effectively synchronizes follicle wave emergence for both superovulation and estrus synchronization, but estradiol benzoate is not available in many countries. The challenge now is to use knowledge of follicle wave dynamics to design alternatives.

Control of ovarian function for assisted reproductive technologies in cattle

Although the discovery that follicles in bovine ovaries grow in a wave-like fashion has presented challenges for estrus synchronization and superovulation, recent protocols, designed to control follicular function have permitted fixed-time AI or fixed-time embryo transfer with high pregnancy rates, and the initiation of superstimulatory treatments at a self-appointed time, all without the necessity of estrus detection. The key is the synchronization of follicle wave emergence. More recent studies have revealed that it is not only possible to synchronize the timing of ovulation for fixed-time AI in single ovulating animals, but also in superstimulated donors. Ultrasound-guided follicle ablation is very efficacious in synchronizing follicle wave emergence but is difficult to apply in the field. Similarly, the induction of ovulation with GnRH or LH will effectively synchronize follicle wave emergence, but ovulation occurs in only 60 to 70% of cases. The administration of estradiol benzoate in progestin-treated cattle effectively synchronizes follicle wave emergence for both superovulation and estrus synchronization, but estradiol benzoate is not available in many countries. The challenge now is to use knowledge of follicle wave dynamics to design alternatives.(AU)