Microsoft word - ar105 ferreira pag 370 a 375.doc

Anim. Reprod., v.3, n.3, p.370-375, Jul./Sept. 2006 Effect of synchronizing ovulation in cattle administered a norgestomet ear implant in
association with eCG and estradiol treatments on pregnancy rate after
fixed-time embryo transfer
R.M. Ferreira1,4, C.A. Rodrigues2, H. Ayres3, R.F. Mancilha2, P.H. Franceschini1, C.R. Esper1,
P.S. Baruselli3,4
1Department of Preventive Veterinarian Medicine and Animal Reproduction, FCAV/UNESP, Jaboticabal, SP, Brazil. 3 Department of Animal Reproduction, FMVZ/USP, São Paulo, SP, Brazil. Abstract
cost of maintaining recipients and the time and labor to accomplish all treatments in a fixed-time embryo transfer This study evaluated the effect of changing the (FTET) protocol limit the widespread application and the day of administration of eCG and d-cloprostenol (PGF) success of this technology (Bó et al., 2002). and the replacement of estradiol benzoate (EB) with Previous studies have shown that by using the estradiol cypionate (EC) in fixed-time embryo transfer Ovsynch protocol (Baruselli et al., 2000b) or a (FTET) protocols in order to simplify embryo recipient progesterone (P4)-releasing intravaginal device (Tríbulo management. Three-hundred cycling heifers (Bos et al., 2000; Baruselli et al., 2000a; 2001; Bó et al., taurus x Bos indicus) were allocated to one of three 2001) it is possible to precisely manipulate follicular groups. On a random day of the estrous cycle (D0), and luteal dynamics, thus abolishing the need for estrus all groups received 2 mg of EB and an ear implant detection for artificial insemination (AI; Baruselli et al., containing 3 mg of norgestomet, which was removed on 2002; Martinez et al., 2002; Bó et al., 2003) and for ET. D8. The control group (G-C; n = 100) received 400 IU One approach to increase the overall pregnancy rate is of eCG and 150 µg of PGF on D5 and 1 mg of EB on D9. to elevate circulating progesterone concentrations by Group EB (G-EB; n = 100) received a similar single or multiple ovulations induced by administration protocol, but D5 treatments were postponed until D8. of eCG in association with a P4-releasing intravaginal Group EC (G-EC; n = 100) received the same device during an ovulation synchronization protocol treatments as G-EB, except for the replacement of EB (Fuentes and De la Fuente, 1997; Baruselli et al., 2000a; on D9 with 0.5 mg of EC on D8. Ultrasonographic 2001; Tríbulo et al., 2002). This procedure is supported determination of the number and area of corpora lutea by several studies that found a positive correlation (CLs) was performed on D17 for all groups and was between serum progesterone concentrations and followed by embryo transfer. Recipients with multiple pregnancy rates in cattle (Binelli, et al., 2001; Thatcher CLs or a single CL ≥ 15 mm in diameter received an in et al., 2001; Bó et al., 2002). Recently, Looney et al. vitro produced embryo. Pregnancy was diagnosed by (2006) reported various protocols using eCG or hCG Transferred-to-treated rate was similar among groups concentrations and improve pregnancy rates. Higher (G-C = 92.0%, G-EB = 93.0%, and G-EC = 96.0%). progesterone concentrations have also been associated However, pregnant-to-transferred and pregnant-to- with increased embryo development and the capacity of treated rates were higher (P = 0.03) in G-EC [61.5% the conceptus to produce interferon-τ (Mann et al., (59/96) and 59.0% (59/100)] than in G-C [45.6% 1999), thus improving conception rates (Fuentes and De (42/92) and 42.0% (42/100)] and G-EB [45.2% (42/93) La Fuente, 1997; Baruselli et al., 2001; Santos et al., and 42.0% (42/100)]. As expected, multiple ovulation 2000; Marques et al., 2003). A luteotrophic effect of rate (multiple ovulation-to-treated) in G-C (31.0%) was eCG was also reported in Bos indicus x Bos taurus higher (P = 0.002) than in G-EB (11.0%) and G-EC embryo recipients by increasing both progesterone (13.0%). In conclusion, the modifications to the conventional protocol of FTET reduced animal handling In crossbred Bos taurus x Bos indicus recipients, a conventional synchronization protocol consists of insertion Keywords: fixed-time embryo transfer, norgestomet,
of a P4-releasing intravaginal device plus administration of pregnancy rate, eCG, estradiol cypionate. 2 mg of estradiol benzoate (EB) i.m. on a random day of Introduction
the estrous cycle (designated D0) to synchronize follicular wave emergence, eCG to stimulate follicular Recipients play an important role in the success growth, d-cloprostenol (PGF) on D5 to induce of embryo transfer (ET) programs. However, the high luteolysis, P4-releasing intravaginal device withdrawal __________________________________________________
4Corresponding author: [email protected]; [email protected]
Received: June 1, 2006
Accepted: November 28, 2006
Ferreira et al. Fixed-time embryo transfer. on D8, 1 mg of EB 24 h later to synchronize ovulation, corpus luteum confirmed by ultrasonography), free from and FTET on D17 (Baruselli et al., 2000a). Rodrigues et brucellosis and tuberculosis, and vaccinated against al. (2004) found that the norgestomet ear implant and leptospirosis, foot and mouth disease, clostridiosis, EB treatment on D0 synchronized follicular wave IBR, BVD, PI3, and BRSV, were selected. The experiment emergence and ovulation in heifers destined for FTET. was performed in three replicates (n = 126, n = 120, One attempt to improve ovulation rate was the and n = 54, respectively). All animals were kept on administration of estradiol 24 h after device withdrawal, pasture, supplemented with good quality mineral salt, in order to induce a synchronized LH peak (Hanlon et and had ad libitum access to water. al., 1996; Macmillan and Burke, 1996; Martínez et al., 1999). The administration of EB increased, hastened, Ovulation synchronization and treatments and synchronized ovulation of treated Bos indicus x Bos At the beginning of each replicate, heifers were taurus heifers (Marques et al., 2003). Colazo et al. randomly allocated to one of three treatment groups (n = 100/group). At unknown stages of the estrous cycle administration at the time of P4-releasing intravaginal (D0), all heifers received a norgestomet ear implant device removal induced a synchronous ovulation of the (Crestar, Intervet, Netherlands) plus 2 mg of EB i.m. dominant follicle when the follicular wave was (Estrogin, Farmavet, Brazil) given concurrently. On D5, synchronized with estradiol-17β (E-17β) on D0. the control group (G-C) animals received 400 IU of Preliminary studies on follicular dynamics in eCG i.m. (Folligon; Intervet, Netherlands) and 150 µg Bos indicus cattle (Reis et al., 2004; Martins et al., of d-cloprostenol i.m. (PGF; Preloban; Intervet, 2005) showed that EC administration at the time of Netherlands). On D8, the ear implant was removed and device removal promoted synchronized ovulations 1 mg of EB (i.m.) was administered 24 h later (D9; approximately 70 h later, similar to EB administration Fig. 1). Group EB (G-EB) received the same protocol 24 h after device withdrawal. This finding reinforced used for G-C, except for the administration of eCG and the notion of the ability of EC to synchronize ovulation. PGF at the time of ear implant removal (D8). Group EC Penteado et al. (2005) also compared the use of EC or (G-EC) received the same protocol as G-EB, but the EB EB to synchronize ovulation in fixed-time artificial given on D9 was replaced by the administration of insemination (FTAI) programs using P4-releasing 0.5 mg of EC i.m. (E.C.P.; Pfizer, Brazil) on D8. intravaginal devices and achieved higher pregnancy In the absence of estrus detection, D10 was rates using EC. Marques et al. (2004), in similar study, considered the day of estrus. Embryo transfer of an in and Ayres et al. (2006), having used a norgestomet ear vitro produced embryo was performed for all groups on implant, obtained similar results with both compounds. D17 for recipients with a corpus luteum (CL). Despite advances in conventional recipient synchronization protocols in FTET programs, recipient synchronization still requires frequent animal handling, which may reduce program efficiency. Therefore, the examined using transrectal ultrasonography (Aloka aim of the present study was to compare the use of a SSD-500 console equipped with a 5 MHz linear norgestomet ear implant in addition to EB or EC transducer; Tokyo, Japan) to detect the presence of CLs, treatment and to evaluate the effect of delaying the number of CLs, and the area of a single CL. In heifers administration of eCG and PGF from D5 to D8 in FTET with a single CL, the image with the largest CL protocols. The purpose of these modifications was to diameter was frozen, and its area (including the cavity, when present) was estimated using software integrated Null hypotheses were: (1) recipients that receive in the scanner. In heifers with more than one CL, area of eCG treatment on D5 or D8 (in a protocol using a the CL was not measured. Only heifers with more than norgestomet ear implant) would have the same efficiency one CL or a single CL > 15 mm in diameter were selected to receive an embryo. Ultrasonographic pregnant-to-treated rates) and (2) the replacement of EB pregnancy diagnosis was done 23 d after ET. on D9 with EC on D8 would not affect efficiency. In vitro embryo production and transfer Materials and Methods
Embryos were produced in vitro by a commercial Brazilian company, following standard protocols as previously reported (Dayan et al., 2002). Twenty-one donors and semen of four bulls were used (21 different in vitro fertilization processes) to produce three- commercial farm in southwest Brazil (22o 01’ 27” S and hundred embryos which were transferred during the 47o 53’ 19” W) during August 2005. Crossbred Bos experiment. The same sires were used in all replicates, and indicus x Bos taurus heifers (n = 300) without previous only Grade-1 blastocysts were used. All embryos were service, from 24 to 32 mo of age, having a mean body transferred non-surgically into the uterine horn ipsilateral weight of 315 kg, with ovarian cyclicity (presence of a to the CL by the same veterinarian on D17. Anim. Reprod., v.3, n.3, p.370-375, Jul./Sept. 2006 Ferreira et al. Fixed-time embryo transfer.
Group control (G-C):

Group estradiol benzoate (G-EB):

Group estradiol cypionate (G-EC):
Figure 1. Schemes of treatment protocols (G-C, G-EB and G-EC) for fixed-time embryo transfer recipients. (EB, estradiol benzoate; EC, estradiol cypionate). Statistical analyses sire, or an interaction between replicate and treatment. The effect of treatment on the number of CLs and CL Statistical analyses were performed using the SAS System for Windows (SAS, 2000). Effects of pregnant-to-treated, and multiple ovulation rates are replicates, sires, and interactions between replicates and shown (Table 1). Heifers from Group G-C had the treatments were analyzed. Discrete Dependent variables highest multiple ovulation response and consequently, (i.e. number of CLs and area of a single CL) were analyzed the highest mean number of CLs. Treatment with eCG by ANOVA using the GLM procedure. A chi-square test on D5 (G-C) produced a greater CL area compared to was used to compare rates of transferred-to-treated, eCG administration on D8 (G-EB and G-EC, Table 1). pregnant-to-transferred, pregnant-to-treated, and multiple The proportion of recipients that received an embryo to ovulations (multiple ovulation-to-treated) among groups. those treated was not influenced (P > 0.05) by the conventional one. However, the overall pregnant-to- transferred and pregnant-to-treated rates were higher in There were no significant effects of replicate, recipients from group G-EC (P < 0.05, Table 1). Anim. Reprod., v.3, n.3, p.370-375, Jul./Sept. 2006 Ferreira et al. Fixed-time embryo transfer. Table 1. Mean (± SD) outcomes in three groups of recipient heifers given a norgestomet ear implant and 2 mg of EB (Day 0). 1 In group G-C, heifers were given 400 IU of eCG and PGF on Days 5 (implant removal on Day 8), and 1 mg of EB on Day 9. In the other two groups, Day 5 treatments were given on Day 8, with 0.5 mg of EC on Day 8 (in lieu of EB on Day 9) in group G-EC. a, b Different letters within rows differ significantly. Discussion
Nasser et al. (2004) changed the day of eCG treatment from D5 to D8 but used a P4-releasing intravaginal The impetus for this study was the possibility device; they reported a reduction in transferred-to- to simplify available protocols for FTET. Both null treated, pregnant-to-transferred, and pregnant-to-treated hypotheses were supported; changing the day of eCG rates. This reduction may have been due to higher administration from D5 (G-C) to D8 (G-EB) in Bos indicus x Bos taurus heifers treated with a norgestomet treatment (P4-releasing intravaginal device plus a CL) ear implant and replacing EB on D9 with EC on D8 had resulting in suppression of the dominant follicle (Adams no effect on efficiency of FTET programs. These et al., 1992; Rathbone et al., 2001). This inhibitory changes eliminated handling the cattle on two effect of progesterone on follicular growth in synchronized heifers was confirmed by Carvalho significantly higher in animals in which ovulation was (2004), and it was more pronounced in Bos indicus synchronized using EC at the time of implant removal cattle; these animals, in particular, had higher (G-C) than in those of the other two groups. concentrations of progesterone compared to Bos taurus In this study, we chose to use a norgestomet ear cattle subjected to a similar treatment and management. implant to minimize suppression of follicular growth. Therefore, the success achieved in the present study Norgestomet does not inhibit LH pulse frequency in following changing the day of eCG treatment from D5 contrast to a P4-releasing intravaginal device, which to D8 was attributed to the use of norgestomet, but this suppressed LH pulsatility and follicular growth as is not recommended for progesterone-based protocols. shown by the elegant findings of Kinder et al. (1996) Estradiol cypionate treatment at the time of ear and Rathbone et al. (2001). In a previous study of implant removal produced a satisfactory transferred-to- follicular dynamics that used cycling Nelore (Bos treated rate and a higher pregnancy rate compared to G- indicus) heifers treated with a norgestomet ear implant C and G-EB. The higher pregnancy rate obtained in the or P4-releasing intravaginal device (CIDR), follicular EC-treated group may be related to increased time of growth, maximum diameter of the dominant follicle, exposure to estradiol during the period of follicular and ovulation rate were higher in norgestomet-treated development immediately preceding ovulation, which is heifers (Sá Filho et al., 2005). Furthermore, Torres- critical to enhance luteal lifespan (Day et al., 1990). Junior et al. (2005) synchronized cycling heifers with a Attainment of a threshold concentration of estradiol norgestomet ear implant with or without PGF during the pre-ovulatory period is necessary to allow administration on D0 and the data supported that of the adequate CL formation and maintenance. Potential sites aforementioned work. The addition or not of PGF did of action for estradiol are numerous, including direct not significantly effect dominant follicle diameter on actions on follicular development, effects on uterine D8, dominant follicle maximum diameter, ovulatory function during either the pre-or post-ovulatory period, follicle diameter, ovulation rate, or the interval between and alteration of endocrine support for folliculogenesis implant removal and ovulation. The authors suggested a lack of a suppressive effect of the norgestomet ear Based on studies of follicular dynamics, it does implant when the animals were treated either with or not seem to be relevant whether EC is given at device withdrawal or EB is given 24 h later; the efficiency to Similar to our study, Reis et al. (2004) and synchronize ovulation 70 h after progesterone source Anim. Reprod., v.3, n.3, p.370-375, Jul./ Sept. 2006 Ferreira et al. Fixed-time embryo transfer. removal was similar for both compounds (Reis et al., Madureira EH, Campos Filho EP. 2002. Efeito de
2004; Martins et al., 2005). In a recent study using EC diferentes protocolos de inseminação artificial em for FTAI in Nelore cows, similar pregnancy rates were tempo fixo na eficiência reprodutiva de vacas de corte achieved with EC at the time of implant removal (0.5 or lactantes. Rev Bras Reprod Anim, 26:218-221. 1.0 mg) or EB 24 h later (Ayres et al., 2006). Similarly, Baruselli PS, Marques MO, Madureira EH, Costa
in the present study, EC at the time of implant removal Neto WP, Grandinetti RR, Bó GA. 2001. Increased
was highly efficacious in a FTET protocol. pregnancy rates in embryo recipients treated with Estradiol cypionate was previously used to CIDR-B devices and eCG. Theriogenology, 55:157. synchronize ovulation in heifers in FTAI protocols that used a P4-releasing intravaginal device (Colazo et al., Baruselli PS, Marques MO, Madureira EH, Costa
2003). In that study, synchronized follicular-wave Neto WP, Grandinetti RR, Bó GA. 2000a.
emergence using a P4-releasing intravaginal device plus Superestimulação ovariana de receptoras de embriões E-17β on D0 and induction of ovulation using 0.5 mg of bovinos visando o aumento de corpos lúteos, EC, given at device removal or 24 h later, resulted in concentração de P4 e taxa de prenhez. Arq Fac Vet synchronous ovulation and acceptable pregnancy rates. These data were in agreement with Marques et al. Baruselli PS, Marques MO, Carvalho NAT,
(2003), who used the same protocol in Nelore cows. Valentim R, Berber RCA, Carvalho Filho AF,
Furthermore, similar to our results, Penteado et al. Madureira EH, Costa Neto WP. 2000b. Aumento da
(2005) reported higher pregnancy rates with 1.0 mg of taxa de prenhez em receptoras de embrião bovino pela EC at P4-releasing intravaginal device removal than utilização do protocolo “ovsynch” com inovulação em with EB 24 h later in FTAI protocols using Nelore cows tempo fixo. Arq Fac Vet UFRGS, 28:216. (abstract). (49.4% vs. 41.4%, respectively). Despite such favorable Binelli M, Thatcher WW, Mattos R, Baruselli PS.
results in the present study, further studies are necessary 2001. Antiluteolytic strategies to improve fertility in to confirm whether the improvement in pregnancy rate cattle. Theriogenology, 56:1451-1463. Bó GA, Baruselli PS, Martinez MF. 2003. Pattern and
manipulation of follicular development in Bos indicus norgestomet ear implant with EB at implant insertion cattle. Anim Reprod Sci, 78:307-326. and PGF, eCG, and EC at implant removal on D8 was Bó GA, Tríbulo H, Caccia M, Tríbulo R. 2001.
successfully used for FTET in Bos indicus x Bos taurus Pregnancy rates in embryo recipients treated with recipients. This protocol resulted in a satisfactory progesterone vaginal devices and transferred without proportion of recipients selected and higher pregnancy estrus detection. Theriogenology, 55:357. (abstract). rates when compared to G-C and G-EB, thus optimizing Bó GA, Baruselli PS, Moreno D, Cutaia L, Caccia M,
the use of recipients and facilitating the utilization of ET Tríbulo R, Tríbulo H, Mapletoft RJ. 2002. The
technology. These changes not only reduced the control of follicular wave development for self- frequency of animal handling but also increased appointed embryo transfer programs in cattle. Carvalho JBP. 2004. Sincronização da ovulação com
Acknowledgments
dispositivo intravaginal de progesterona (CIDR) em novilhas B. indicus, B.indicus x B.taurus e B. taurus [in Portuguese]. São Paulo, SP: Universidade de São Paulo. employees of Fazenda Santa Rita and Fazenda Ibicatu, Descalvado/SP, Fazenda Santa Eliza, Analândia, SP for Colazo MG, Kastelic JP, Mapletoft RJ. 2003. Effects
infrastructure and animal care, Intervet of Brazil for of estradiol cypionate (ECP) on ovarian follicular supporting the research, and to Dr. S.R.G. Ferreira for dynamics, synchrony of ovulation, and fertility in CIDR-based, fixed-time AI programs in beef heifers. References
Day ML, Dyer RM, Wilson GW, Pope WF. 1990.
Influence of estradiol on duration of anestrus and Adams GP, Matteri RL, Ginther OJ. 1992. The effect
incidence of short estrous cycles in postpartum cows. of progesterone on growth of ovarian follicles, emergence of follicular waves and circulating FSH in Dayan A, Watanabe MR, Ferraz ML, Meirelles FV,
heifers. J Reprod Fertil, 95:627-640. Watanabe YF. 2002. Influence of the embryo stage,
Ayres H, Penteado L, Torres-Júnior JR, Souza AH,
development kinetics and recipient synchronization on Baruselli PS. 2006. Taxa de concepção de vacas nelore
pregnancy rates of OPU-IVP embryos. Theriogenology, lactantes sincronizadas com implante auricular de progestágeno associado ao benzoato ou ao cipionato de Fuentes S, De la Fuente J. 1997. Different
estradiol. Acta Sci Vet, 34:410. (abstract).
synchronization treatments for direct embryo transfer to Baruselli PS, Marques MO, Carvalho NAT,
recipient heifers. In: Proceedings of the 13th Annual Anim. Reprod., v.3, n.3, p.370-375, Jul./ Sept. 2006 Ferreira et al. Fixed-time embryo transfer. Meeting of the European Embryo Transfer Association, 1997, Lyon, France. Lyon: AETE. pp.148. (abstract). Rathbone MJ, Kinder JE, Fike K. 2001. Recent
Hanlon DW, Williamson NB, Wichtel JJ, Steffert IJ,
advances in bovine reproductive endocrinology and Craigie AL, Pfeiffer DU. 1996. The effect of estradiol
physiology and their impact on drug delivery system design for the control of the estrous cycle in cattle. Adv synchronized pregnancy rate in dairy heifers after treatment with exogenous progesterone. Theriogenology, 45:775-785. Reis EL, Gimenes LU, Marques MO, Carvalho JBP,
Kinder JE, Kojima FN, Bergfeld EGM, Wehrman
Mapletoft RJ, Baruselli PS. 2004. Efeitos do
ME, Fike KE. 1996. Progestin and estrogen regulation
Cipionato e do Benzoato de estradiol na dinâmica of pulsatile LH release and development of persistent folicular e luteínica de vacas nelore. Acta Sci Vet, ovarian follicles in cattle. J Anim Sci, 74:1424-1440. Looney CR, Nelson JS, Schneider HJ, Forrest DW.
Rodrigues CA, Ayres H, Reis EL, Madureira EH,
2006. Improving fertility in beef cow recipients. Baruselli PS. 2004. Aumento da taxa de prenhez em
vacas Nelore inseminadas em tempo fixo com o uso de Macmillan KL, Burke CR. 1996. Effects of estrous
eCG em diferentes períodos pós-parto. Acta Sci Vet, cycle control on reproductive efficiency. Anim Reprod Sá Filho MF, Gimenes LU, Ayres H, Carvalho JB,
Mann GE, Lamming GE, Robinson RS, Wathes DC.
Carvalho NAT, Baruselli PS. 2005. Dinâmica folicular
1999. The regulation of interferon-τ production and de novilhas Bos indicus tratadas com implante auricular uterine hormone receptors during pregnancy. J Reprod de Norgestomet ou com dispositivo intravaginal de progesterona. Acta Sci Vet, 33:266. (abstract). Marques MO, Ayres H, Reis EL, Mapletoft RJ,
Santos JEP, Thatcher WW, Poll L, Overton MW,
Baruselli PS. 2004. Efeito do cipionato e do benzoato de
Reynolds JP. 2000. Human chorionic gonadotropin
estradiol na taxa de prenhez de vacas nelore inseminadas em tempo fixo. Acta Sci Vet, 32:222. (abstract). progesterone and conception rates of dairy cows. In: Marques MO, Nasser LF, Silva RCP, Bó GA,
Proceedings of the 14th International Congress on Baruselli PS. 2003. Increased pregnancy rates in Bos
Animal Reproduction, Stockholm, Sweden. Stockholm: taurus x Bos indicus embryo recipients with treatments SAS user’s guide: statistics version 8.0. 2000. Cary,
Theriogenology, 59:369. (abstract). Martins CM, Castricini ESC, Sá Filho MF, Gimenes
Thatcher WW, Moreira F, Santos JEP, Mattos RC,
LU, Baruselli PS. 2005. Dinâmica folicular de vacas
Lopez FL, Pancarci SM, Risco CA. 2001. Effects of
nelore tratadas com Cipionato ou Benzoato de estradiol hormonal treatments on reproductive performance and em protocolos de inseminação artificial em tempo fixo. embryo production. Theriogenology, 55:75-90. Acta Sci Vet, 33:285. (abstract). Torres-Júnior JRS, Sá Filho MF, Gimenes LU,
Martinez MF, Adams GP, Bergfelt D, Kastelic JP,
Madureira EH, Baruselli PS. 2005. Efeito da
Mapletoft RJ. 1999. Effect of LH or GnRH on the
administração de PGF2α no início do tratamento com dominant follicle of the first follicular wave in heifers. implante auricular de Norgestomet na dinâmica folicular de novilhas nelore (Bos indicus). Acta Sci Vet, Martinez MF, Kastelic JP, Adams GP, Cook RB,
Olson WO, Mapletoft RJ. 2002. The use of progestins
Tríbulo H, Moreno D, Cutaia L, Gatti G, Tríbulo R,
in regiments for fixed-time artificial insemination in Caccia M, Bó GA. 2002. Pregnancy rates in embryo
beef cattle. Theriogenology, 57:1049-1059. recipients treated with progesterone vaginal device and Nasser LF, Reisa EL, Oliveira MA, Bó GA, Baruselli
PS. 2004. Comparison of four synchronization protocols
Theriogenology, 57:563. (abstract). for fixed-time bovine embryo transfer in Bos indicus x Tríbulo H, Bó GA, Gatti G, Tegli JC, Cutaia, L,
Bos taurus recipients. Theriogenology, 62:1577-1584. Moreno D, Brito M, Tríbulo R. 2000. Pregnancy rates
Penteado L, Sá Filho MF, Martins CM, Gimenes LU,
in embryo recipients treated with Estradiol benzoate and Ayres H, Baruselli PS. 2005. Variação na taxa de
CIDR-B vaginal device to eliminate the need for estrus concepção de vacas nelore lactantes sincronizadas com detection. In: Proceedings of the 14th International dispositivo intravaginal de progesterona associado ao Congress on Animal Reproduction, Stockholm. Sweden. benzoato ou ao cipionato de estradiol. Acta Sci Vet, Stockholm: ICAR. vol.2, pp.115. (abstract) Anim. Reprod., v.3, n.3, p.370-375, Jul./ Sept. 2006

Source: http://www.delavidaboran.co.za/article_synchronizing%20ovulation.pdf