Comparison of the pregnancy rates and costs per calf born after fixed-time artificial insemination or artificial insemination after estrus detection in Bos indicus heifers

This study compared pregnancy rates (PRs) and costs per calf born after fixed-time artificial insemination (FTAI) or AI after estrus detection (i.e., estrus detection and AI, EDAI), before and after a single PGF2α treatment in Bos indicus (Brahman-cross) heifers. On Day 0, the body weight, body condition score, and presence of a CL (46% of heifers) were determined. The heifers were then alternately allocated to one of two FTAI groups (FTAI-1, n = 139) and (FTAI-2, n = 141) and an EDAI group (n = 273). Heifers in the FTAI groups received an intravaginal progesterone-releasing device (IPRD; 0.78 g of progesterone) and 1 mg of estradiol benzoate intramuscularly (im) on Day 0. Eight days later, the IPRD was removed and heifers received 500 μg of PGF2α and 300 IU of eCG im; 24 hours later, they received 1 mg estradiol benzoate im and were submitted to FTAI 30 to 34 hours later (54 and 58 hours after IPRD removal). Heifers in the FTAI-2 group started treatment 8 days after those in the FTAI-1 group. Heifers in the EDAI group were inseminated approximately 12 hours after the detection of estrus between Days 4 and 9 at which time the heifers that had not been detected in estrus received 500 μg of PGF2α im and EDAI continued until Day 13. Heifers in the FTAI groups had a higher overall PR (proportion pregnant as per the entire group) than the EDAI group (34.6% vs. 23.2%; P = 0.003), however, conception rate (PR of heifers submitted for AI) tended to favor the estrus detection group (34.6% vs. 44.1%; P = 0.059). The cost per AI calf born was estimated to be $267.67 and $291.37 for the FTAI and EDAI groups, respectively. It was concluded that in Brahman heifers typical of those annually mated in northern Australia FTAI compared with EDAI increases the number of heifers pregnant and reduces the cost per calf born.

Comparison of Various Methods of Estrus Detection in Synchronized Virgin Beef Heifers

Methods of heat detection were compared in the Mid- Crest Area Cattle Evaluation Program (MACEP) heifer development program in the 1998-breeding season. A total of 189 heifers from thirteen consignors entered the program on November 10, 1997. These heifers were condition scored, hip height measured, weighed, disposition scored, booster vaccinated, and treated for parasites at the time of arrival. Determination of the heifer’s mature weight was made and a target of 65% of their mature weight at breeding was established. The ration was designed to meet this goal. The heifers were kept in a dry lot until all heifers were AI bred once. The heifers were periodically weighed and condition scored to monitor their gains and the ration was adjusted as needed. The estrus synchronization program consisted of an oral progesterone analog for 14 days; 17 days after completion of the progesterone analog treatment a single injection of prostaglandin was given and the heifers were then estrus detected. Two concurrent methods of estrus detection were utilized: 1) Ovatec â electronic breeding probe (probe), 2) HeatWatchâ estrus detection system (HW), and 3) a combination of probe and HW. Probe readings were obtained each 12 hours and the heifers were continuously monitored for estrus activity using the HW system. The probe was used as the primary estrus detection method and the HW system was used as a back-up system. Those heifers that did not demonstrate any estrus signs prior to 96 hours post prostaglandin treatment were mass inseminated at 96 hours. Post AI breeding, 151 of the heifers were placed on pasture and ran with clean-up bulls for 60 days. The remaining heifers left the program after the AI breeding was completed. Pregnancy to the AI breeding was determined by ultrasound on June 29, 1998. Results from using both probe and HW were 60% pregnant by AI, probe alone was 32% pregnant by AI, and HW alone was 27% pregnant by AI. The result of mass insemination was 20% pregnant by AI.

Strategies for Artificial Insemination of Cattle at Synchronized Ovulation or Synchronized Estrus

Two synchronization protocols in lactating dairy and beef cows and in dairy heifers were tested for efficacy of breeding by artificial insemination (AI) with or without estrus detection. Controls received three prostaglandin F2a (PGF2a) injections 14 days apart before AI at observed estrus. Pregnancy rates were compared with animals on the Ovsynch protocol that combined gonadotropin releasing hormone (GnRH) and PGF2a treatments with a timed AI 16 to 20 hours after the second GnRH injection. The pregnancy rates were similar at synchronized ovulation to fixed-time AI in lactating cows, but not effective in heifers because of the lack of synchronization.

Superovulation and embryo collection in nulliparous Boer goat does immunized against a recombinant ovine alpha-subunit inhibin

With the purpose of eliciting a superovulatory response, 12 adult nulliparous Boer goat does were actively immunized against a recombinant a-subunit of ovine inhibin (roIHN-alpha; two injections of 100 mg 4 weeks apart). Another 12 control Boer goat does were treated with physiological saline and acted as controls. One year later the immunized animals were boostered by the administration of another dose (100 mg) of the immunogen. Following treatment, blood samples were collected twice weekly for the periods of 16 and 12 weeks, respectively, to monitor the inhibin binding ability with the aid of a radio-tracer binding assay. Throughout the experiment, estrus detection was conducted twice daily with the aid of an aproned intact buck. From the first day after treatment to 48 h after standing estrus, ovarian activity was monitored daily by transrectal ultrasonography. On alternate estrous cycles, does were mated and 6 days later flushed transcervically to recover embryos. All goats treated with the roIHN-alpha produced antibodies reactive to the native bovine inhibin tracer-the titre increasing from 2.9 +/- 0.4 to a maximum of 21.9 +/- 2.9% binding after the second injection. The antibody titre gradually subsided over the next 16 weeks. The booster injection restored an elevated antibody titre (11.7 +/- 0.4%), which was maintained until the end of the sampling period 12 weeks later. In the control goats only trace amounts of antibody were recorded throughout the trial. In the roIHN-alpha-immunized goats the number of follicles reaching a diameter of > 4 mm was 14.6 +/- 1.2 per doe. A positive correlation was recorded between the follicle number and antibody titre (r=0.61; P < 0.01). The number of follicles ovulating per doe (6.9 +/- 0.7) followed the same tendency-however, the proportion decreased with increasing follicle numbers. A relatively weak correlation was recorded between the inhibin binding ability and number of ovulations (r=0.27; P < 0.05). In the control goats the majority (92%) of follicles exceeding 4 mm in diameter ovulated (2.5 +/- 0.1 follicles/doe). Embryo collection proved unsatisfactory (42% versus 39% recovery for immunized and control animals, respectively)-presumably because the uterine lumen of the nulliparous does was too narrow to permit effective flushing. In the group of immunized goats the occurrence of short estrous cycles (< 15 days) recorded was 34% versus only 6% in the controls. Overall, immunization of goats against roIHN-alpha led to an almost six-fold increase in number of ovarian follicles, a three-fold increase in ovulations and, despite the low recovery rate, a more than three-fold increase in ova or embryos recovered. It may be concluded that treatment of female goats with roIHN-alpha leads to an inhibin antibody response, accompanied by enhanced ovarian activity. The response was, however, accompanied by a large proportion of retained follicles and a high incidence of short estrous cycles. These problems need to be further investigated before rendering the method fit for application in embryo transfer programs in goats. (C) 2007 Elsevier B.V. All rights reserved.

Fertility Rates Following Fixed-Time Artificial Insemination in Dairy Heifers in a Practical Progesterone-Based Protocol

Background: In bovines, more efficient management practices are important for maximizing profitability. In order to increase the pregnancy rates in artificial insemination (AI) programs, several hormonal protocols were developed to synchronize the follicular wave and the moment of ovulation in beef and dairy cattle. In dairy cattle, detection of estrus can be difficult due to a number of factors including the incidence of silent estrus. Hormonal treatments designed to control both luteal and follicular function has permitting efficient synchronizations of time of ovulation. Thus, the AI can be performed in a large number of animals on a fixed schedule without the need for detection of estrus. Using these management techniques, the fixed-time artificial insemination (TAI) can overcome the problem of accurate estrus detection and help in reducing the incidence of repeat breeding. In addition, with TAI in cattle operations, it is possible to facilitate management practices and commercialization, and to reduce the time and semen wasting with animals inseminated at incorrect times. The investigation of practical and efficient TAI protocols is important for reducing the labor and animal handling of TAI in dairy cattle, as well as for increasing the profitability of the cattle management system. This study was carried out in order to investigate the effectiveness of TAI in dairy heifers treated with a practical progesterone-based protocol.Materials, Methods & Results: This experiment was conducted at the university farm located in southwestern Brazil, during May 2009. Thirty-nine cycling crossbred dairy heifers were employed in this study. All animals received a single intramuscular injection of estradiol benzoate and intravaginal progesterone releasing device in a random stage of the estrous cycle (Day 0). on day 7 the animals were treated with PGF2a analogue and on day 9 the device was removed. Forty-eight hours after the device removal (day 11) a synthetic analogue of GnRH was administered and the animals were fixed-time artificially inseminated at the time of GnRH injection. The inseminations were performed using four different batches from the same Holstein bull. Among the heifers that were synchronized (87.2%), 30.8% ovulated until 24 h after TAI and 56.4% ovulated between 24 and 32 h after TAI. The conception rate was 61.5%. No effects of ovulation time in conception rates were detected. The conception rate from heifers that ovulated until 24 h after TAI was 58.3% and from heifers that ovulated between 24 and 32 h after TAI was 77.3%. The mean of ovulatory follicle in heifers that ovulated until 24 h was 14.3 mm and in heifers that ovulated between 24 and 32 h was 11.9 mm.Discussion: Taking together, the findings of the present study, along with those of others, emphasize the concept that development of practical methods for TAI offers significant advantages to dairy producers if conception rates are close or greater to those obtained after breeding at detected estrus. Thus, the results of the present study reinforce the possibility of making dairy cattle production more cost-effective using TAI. In conclusion, with the progesterone-based TAI protocol of the present experiment all synchronized animals ovulated up to 32 h after GnRH+TAI and no effects of ovulation time related to conception rate was detected. The exogenous control of luteal and follicular development facilitated the reproductive management and animal handling. Also, inseminating the heifers at the moment of GnRH injection in a progesterone-based TAI protocol is a practical strategy and provided satisfactory results regarding ovulation and conception rates in dairy heifers.

Influence of sire and sire breed (Gyr versus Holstein) on establishment of pregnancy and embryonic loss in lactating Holstein cows during summer heat stress

Heat stress has negative effects on pregnancy rates of lactating dairy cattle. There are genetic differences in tolerance to heat stress; Bos taurus indicus (B. t. indicus) cattle and embryos are more thermotolerant than Bos taurus taurus (B. t. taurus). In the present study, the effects of sire and sire breed on conception and embryonic/fetal loss rates of lactating Holstein cows during the Brazilian summer were determined. In Experiment 1, cows (n = 302) were AI after estrus detection or at a fixed-time with semen from one Gyr (B. t. indicus) or one Holstein sire (B. t. taurus). Pregnancy was diagnosed 80 days after AI. In Experiment 2, cows (n = 811) were AI with semen from three Gyr and two Holstein sires. Pregnancy was diagnosed at 30-40 and at 60-80 days after AI. Cows diagnosed pregnant at the first examination but non-pregnant at the second were considered as having lost their embryo or fetus. Data were analyzed by logistic regression. The model considered the effect of sire within breed, sire breed, days postpartum, period of lactation, and AI type (AI after estrus versus fixed-time). There was no effect of the AI type, days postpartum or milk production on conception or embryonic loss rates. The use of Gyr bulls increased pregnancy rate when compared to Holstein bulls [9.1% (60/657) versus 5.0% (23/456), respectively, P = 0.008; data from Experiments 1 and 2 combined]. Additionally, in Experiment 2, cows inseminated using semen from sire #4 (Gyr) had lower embryonic loss (10%) when compared with other B. t. indicus (35.3% and 40%) or B. t. taurus sires (18.2% and 38.5%, P = 0.03). In conclusion, the use of B. t. indicus sires may result in higher conception rates in lactating Holstein cows during summer heat stress. Moreover, sire can affect embryonic loss and selection of bulls according to this criterion may result in higher parturition rates in lactating Holstein cows. (c) 2006 Elsevier B.V. All rights reserved.

Reproductive performance of prepubertal Bos indicus heifers after progesterone-based treatments

The objective was to evaluate the effects of exogenous progesterone (P4) on reproductive performance of prepubertal Bos indicus heifers. Prepubertal Nelore heifers (n = 589; 24.0 +/- 1.13 mo; 298.0 +/- 1.89 kg; body condition score of 3.2 +/- 0.26; mean +/- SEM) were randomly assigned to receive, between experimental Days -12 and 0: no treatments (CIDR0; n = 113); a new intravaginal insert (CIDR) containing 1.9 g of P4 (CIDR1; n = 237); or a similar insert previously used three times, with each use occurring for 9 d (CIDR4; n = 239). An additional treatment group was pubertal heifers given 12.5 mg dinoprost tromethamine im on Day 0 (PGF; n = 346), and used as controls for evaluation of conception rates. on Day 0, transrectal palpation was done for uterine score evaluation (UtS; 1-3 scale), blood samples were taken for serum P4 concentrations, and follicle diameter (FD) was measured. The breeding season started on Day 1 and consisted of AI after detection of estrus between Days I and 45, and exposure to bulls between Days 46 and 90. There were effects of treatment (P < 0.05) on serum concentrations of P4 on Day 0 (0.37 +/- 0.16, 2.31 +/- 0.11, and 1.20 +/- 0.11 ng/mL for CIDR0, CIDR1, and CIDR4, respectively; mean SEM), FD on Day 0(9.45 +/- 0.24, 9.72 +/- 0.17, and 11.42 +/- 0.16 mm), UtS on Day 0 (1.49 +/- 0.06, 1.88 +/- 0.04, and 2.24 +/- 0.04), estrus detection rates at 7 d (19.5, 42.6, and 38.3%) and 45 d (52.2, 72.1, and 75.3%) of the breeding season, and on pregnancy rates at 7 d (5.3, 14.3, and 18.4%), 45 d (27.4, 39.2, and 47.7%) and 90 d (72.6, 83.5, and 83.7%) of the breeding season. Conception rate 7 d after the start of the breeding season was greater (P < 0.05) in heifers from the CIDR4 (46.8%) and PGF (43.8%) groups than in the CIDR0 (27.3%) and CIDR1 (33.7%) groups. In conclusion, exogenous P4 hastened puberty and improved pregnancy rates at the beginning of the breeding season in prepubertal Bos indicus heifers. Furthermore, previously used CIDR inserts were better than new inserts. (C) 2010 Elsevier B.V. All rights reserved.

Dinâmica folicular e momento da ovulação em vacas não lactantes das raças Gir e Nelore durante duas estações do ano

Estudou-se o efeito da estação do ano na dinâmica folicular e no momento de ovulação utilizando-se 25 vacas não lactantes da raça Gir (10 no inverno e 15 no verão) e 15 vacas não lactantes da raça Nelore (sete no inverno e oito no verão), todas com ciclo estral normal. Após a detecção do estro, as vacas foram submetidas a exames ultra-sonográficos a cada seis horas com a finalidade de monitorar o momento de ovulação e, posteriormente, uma vez ao dia durante todo o ciclo estral, sendo monitorado um ciclo estral por animal e por estação do ano. As características foliculares não foram afetadas pela estação do ano e não diferiram entre as raças. Houve maior percentagem de ciclos com três (68,0 e 66,7%) e duas ondas foliculares (24,0 e 26,7%) nas raças Gir e Nelore, respectivamente. Os intervalos entre estros e entre ovulações foram menores para ciclos com duas ondas foliculares. A manifestação do estro ocorreu mais nas primeiras horas da manhã (57,3%) e no final da tarde e início da noite (28,0%). O momento de ovulação ocorreu 23,1±5,6 horas após a detecção do estro nas duas raças.

Superovulation and embryo transfer in Bos indices cattle

Compared to Bos taurus breeds, Bos indices breeds of cattle present several differences in reproductive physiology. Follicular diameter at deviation and at the time of ovulatory capability are smaller in B. indicus breeds. Furthermore, B. indicus breeds have a greater sensitivity to gonadotropins, a shorter duration of estrus, and more often express estrus during the night. These differences must be considered when setting up embryo transfer programs for B. indicus cattle. In recent studies, we evaluated follicular dynamics and superovulatory responses in B. indicus donors with the objective of implementing fixed-time AI protocols in superstimulated donors. Protocols using estradiol and progesterone/progestrogen releasing devices to control follicular wave emergence were as efficacious as in B. taurus cattle, allowing the initiation of superstimulatory treatments (with lower dosages of FSH than in B. taurus donors) at a self-appointed time. Furthermore, results presented herein indicate that delaying the removal of progesterone/progestogen-releasing devices, combined with the administration of GnRH or pLH 12 h after the last FSH injection, results in synchronous ovulations, permitting the application of fixed-time AI of donors without the necessity of estrus detection and without compromising the results. (c) 2005 Elsevier B.V. All rights reserved.

Taxa de prenhez de vacas Nelore lactantes tratadas com progesterona associada à remoção temporária de bezerros ou aplicação de gonadotrofina coriônica eqüina

Avaliaram-se os efeitos da remoção temporária de bezerros (RTB) ou da aplicação de gonadotrofina coriônica eqüina (eCG) na taxa de prenhez (TP) de vacas Nelore lactantes tratadas com um dispositivo intravaginal liberador de progesterona (DILP). No experimento 1, 83 vacas Nelore e 102 mestiças (Nelore × Red Angus) foram distribuídas em três grupos. em dia aleatório do ciclo estral (D0), os animais do grupo 1 foram tratados com benzoato de estradiol (BE; 2,5 mg, IM, Estrogin®) e um DILP (1 g de progesterona, DIB®), removido no D9, quando também se administrou d-cloprostenol (150 µg, IM, Prolise®) e aproximadamente 12 horas após identificação do estro realizou-se a inseminação artificial. No grupo 2 (IATF), o tratamento foi semelhante ao aplicado no grupo 1, porém, administrou-se uma segunda dose de benzoato de estradiol (1 mg) no D10 e 30-36 horas mais tarde realizou-se a inseminação artificial em tempo fixo (IATF). No grupo 3 (IATF/RTB), os bezerros foram removidos a partir do D9 até a inseminação artificial com tempo fixo (IATF). As taxas de prenhez para as vacas Nelore e mestiças foram, respectivamente, de 7,69 e 41% (Controle); 23,52 e 59,57% (IATF); 69,44 e 55,81% (IATF/RTB). No experimento 2, 255 vacas Nelore lactantes foram distribuídas em três grupos. Os animais do grupo 4 (IATF) foram tratados com benzoato de estradiol (2 mg) e um DILP (1,9 g de progesterona, CIDR-B®) no D0 e no D8 sofreram remoção do DILP no D8 e administração de 25 mg de dinoprost (IM, Lutalyse®). No D9, foi aplicado benzoato de estradiol (1 mg) realizando-se a IATF 30-36 horas mais tarde. No grupo 5 (IATF/RTB), os bezerros foram removidos no D9 até a IATF. O grupo 6 (eCG) foi semelhante ao IATF, exceto pela aplicação de eCG no D9 (400 UI, IM, Novormon®). As taxas de prenhez foram de 50,57 (IATF), 53,57 (IATF/RTB) e 54,76% (eCG). A associação de RTB ao tratamento hormonal com DILP aumenta as taxas de prenhez, enquanto a adição de eCG ao tratamento não melhora as taxa de prenhez de vacas Nelore lactantes ciclando e em boa condição corporal.

The effect of type of vaginal insert and dose of pLH on embryo production, following fixed-time AI in a progestin-based superstimulatory protocol in Nelore cattle

The objective was to analyze and report field data focusing on the effect of type of progesterone-releasing vaginal insert and dose of pLH on embryo production, following a superstimulatory protocol involving fixed-time artificial insemination (FTAI) in Nelore cattle (Bos taurus indicus). Donor heifers and cows (n = 68; 136 superstimulations over 2 years) received an intravaginal, progesterone-releasing insert (CIDR® or DIB®, with 1.9 or 1.0 g progesterone, respectively) and 3-4 mg of estradiol benzoate (EB) i.m. at random stages of the estrous cycle. Five days later (designated Day 0), cattle were superstimulated with a total of 120-200 mg of pFSH (Folltropin-V®), given twice daily in decreasing doses from Days 0 to 3. All cattle received two luteolytic doses of PGF2α at 08:00 and 20:00 h on Day 2 and progesterone inserts were removed at 20:00 h on Day 3 (36 h after the first PGF2α injection). Ovulation was induced with pLH (Lutropin-V®, 12.5 or 25 mg, i.m.) at 08:00 h on Day 4 with FTAI 12, 24 and in several cases, 36 h later. Embryos were recovered on Days 11 or 12, graded and transferred to synchronous recipients. Overall, the mean (±S.E.M.) number of total ova/embryos (13.3 ± 0.8) and viable embryos (9.4 ± 0.6) and pregnancy rate (43.5%; 528/1213) did not differ among groups, but embryo viability rate (overall, 70.8%) was higher in donors with a DIB (72.3%) than a CIDR (68.3%, P = 0.007). In conclusion, the administration of pLH 12 h after progesterone removal in a progestin-based superstimulatory protocol facilitated fixed-time AI in Nelore donors, with embryo production, embryo viability and pregnancy rates after embryo transfer, comparable to published results where estrus detection and AI was done. Results suggested a possible alternative, which would eliminate the need for estrus detection in donors. © 2006 Elsevier Inc. All rights reserved.

Eficiência do protocolo Ovsynch em ovelhas da raça Santa Inês

Twenty six Santa Inês ewes were asigned to three treatments to evaluate the efficiency of the Ovsynch protocol. In the treatment 1 - control (n=8), the estrus was synchronized with sponges containing 60 mg MAP for 14 days. On D14, 300 IU eCG were administered. In treatment 2 (n=9) the Ovsynch protocol was used: 25 μg of GnRH (D0), 37.5 μg of PGF2α (D7) and 25 μg of GnRH (D9). In treatment 3 (n=9) the modified Ovsynch protocol was used: the administration of PGF2α and second GnRH as two days early. Estrus detection was accomplished using teaser. All ewes were mated twice with 12 hours of interval. Pregnancy rate (PR) was evaluated by ultrasonography 30 days after the end of mating. Estrus response was of 88.46% on average, and without differences among treatments (p>0.05). The interval for onset of estrus was greater (p<0.05) in T1, when compared with T2 and T3 (41.31±7.2, 13.37±8.42 and 6.75±5.2 h, respectively). The time of receptivity was greater (p<0.05) in females of T1 and T3 (40.5±6.49 h and 53.68±10.27 h, respectively), compared to females of T2 (34.56±7.2 h). The duration of the induced estrus did not differ significant among treatments (p>0.05). Pregnancy rate was significantly greater (p<0.05) in ewes synchronized with Ovsynch protocol (37.5%, 62.5% and 25% for treatment 1, 2 and 3, respectively). The results show superior efficiency of the Ovsynch protocol, under the experimental conditions.

Use of LH or eCG in the last day of superestimulatory treatment

In the last decades several hormonal treatments to induce multiple ovulation and embryo transfer (MOET) have been developed. Tight control of the time of ovulation allowed the use of fixed-time artificial insemination (FTAI) in embryos donors, facilitating animal management. Although, protocols that allow FTAI have evolved and yield as much embryo as conventional protocols that requires estrus detection, substantial increase in viable embryo production has not been observed in superestimulated bovine cattle. The present mini-review put emphasis on superstimulatory protocols in which the last two doses of pFSH are replaced by eCG or LH. Recent results indicate that an extra LH stimulus (using eCG or LH), on the last day of P-36 superestimulatory treatment, seems to improve transferable embryo yield in both Bos taurus and Bos indicus cattle.

How FTAI and FTET impact reproductive efficiency of Brazilian dairy herds

Background: Throughout dairy cows evolution, milk production was always the key point to select the superior animal. Currently, several evidences has shown that high milk production have intensively contributed to the decline of dairy cattle fertility. Beyond milk production, dairy cows have their reproductive performance impaired by another factors, heat stress and repeat-breeding. Methods like fixed time artificial insemination and embryo transfer were developed to minimize the effects of these factors, and improve dairy herds profitability. This review aims to show some key-point experiments conducted to improve the efficiency of the self-appointed protocols for artificial insemination and embryo transfer in Brazil, overcoming several reproductive problems. Our goal is to develop cheap and easy self-appointed programs that facilitate animal handling and maximize their reproductive outcomes all over the year. Review: Failure in estrus detection is the mainly limiting factor for the use of artificial insemination in high-production dairy herd. An excellent alternative to overcome the need of estrus detection is fixed time artificial insemination. Many protocols with and without the use of estradiol have been developed to that end. Among the protocols for fixed time artificial insemination without estradiol, DoubleOvsynch has been extensively used recently in American dairy herds. In Brazil, similar pregnancy rate was obtained compared to progesterone-estradiol based protocols for fixed time artificial insemination. Particularities of progesterone-estradiol based protocols as (1) new progesterone device or devices previously used for eight days; (2) different doses of eCG; and (3) the use of estradiol cypionate for fixed time artificial insemination have been studied in Brazil. The use of self-appointed artificial insemination also enabled the reduction of the interval calving-conception compared to cows inseminated following the standing estrus. Regarding the low fertility of repeat breeders and the effect of heat stress at early pregnancy, other methods like embryo transfer became important tools to enhance reproductive efficiency of Brazilian dairy herds. Protocols were also developed to allow fixed time embryo transfer, eliminating the need of estrus detection and improving the reproductive efficiency of lactating recipients. As well as described for fixed time artificial insemination treatments, there is a large variety of hormone combination for fixed time embryo transfer (with and without estradiol). An experiment conducted in Brazil demonstrated that protocols for fixed time embryo transfer without estradiol can be as good as with estradiol to synchronize high-producing Holstein recipients, essentially during summer. Particularities related to embryos cryopreservation, synchronization of the estrus cycle of donors and recipients and the site of embryo release into the uterine horn were also investigated. Greater conception rates were achieved when fresh embryos were transferred compared to frozen-thawed ones. Also, the tight synchronization between donor and recipient (same day of estrus) resulted more pregnancies than when recipients were one day later or in advantage in relation to donors. Moreover, the site of embryo release into the uterine horn (ipsilateral to the corpus luteum) had no effect on pregnancy rates after in vivo produced embryo transfer. Conclusion: Both fixed time artificial insemination and fixed time embryo transfer are important tools to improve reproductive efficiency of high-producing dairy cows. These biotechnologies help bypassing some of the greatest challenges of dairy cattle reproduction: the difficulties of estrus detection, and the low fertility associated to heat stress and repeat breeding.