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Background : Progesterone (P4) is essential for embryonic development and maintenance of pregnancy when deficiency causes early embryonic loss. In this study, we investigated the ability of hormonal supplementation to improve the fertility of cows subjected to fixed-time artificial insemination (IATF) protocols. Here, we evaluated the effect of long-acting injectable progesterone (iP4) supplementation in the D4 after IATF on pregnancy rate and pregnancy loss in Nellore cows ( Bos taurus indicus ) from different reproductive categories in Western Amazonia. Materials, Methods & Results : Eight hundred thirteen animals from 5 farms were selected and distributed into 2 groups: control [GC; administration of 0.5 mL of 0.9% saline solution, intramuscularly – IM] (n = 407) and a group that received injectable progesterone (iP4) that was long-acting [GiP4; administration of 0.5 mL of iP4, 300 mg, via IM four days after IATF] (n = 406). Each group contained 3 subgroups: heifers, primiparous cows, and multiparous cows. Of the 407 animals in the CG, 103 were heifers, 107 primiparous, and 197 multiparous. Of the 406 animals in the GiP4 group, there were 101 heifers, 107 primiparous, and 198 multiparous. On a random day of the estrous cycle (D0), an intravaginal device containing 1 g of P4 and 2 mg of estradiol benzoate (BE) was inserted by intramuscular injection. On D8, the P4 device was removed and 150 μg of D-cloprostenol (PGF2α), 300 IU eCG, and 1 mg BE were administered IM. Cows were inseminated at D10, 48-52 h after procedure on D8. Pregnancy diagnosis was made between 35 and 40 days after insemination through ultrasound examination. Between 80 and 90 days after insemination, a new ultrasound examination was performed to assess early pregnancy loss. The data were processed using the SAS 9.2. The conception rate, pregnancy loss, and final conception rate were analyzed using PROC GLIMMIX according to groups (CG and GiP4), categories (heifers, primiparous and multiparous), and their interactions as variables. The differences in the means of least squares were adjusted using the Tukey–Kramer method. Statistical significance was defined as P < 0.05. The general conception rate was 46% (375/816). Regardless of the animal class, GiP4 animals (51.97%) had higher conception rates ( P < 0.05) than CG (40.29%). In the subgroups (heifers, primiparous and multiparous cows), there was a difference ( P < 0.05) between animals treated with iP4 (52.48%, 57.94%, and 48.48%, respectively) and those who were not (39.81%, 41.12%, and 40.10%, respectively). Gestational losses, regardless of the animal class, were higher in females in the CG (7.93%) [ P < 0.05] compared to those in the GiP4 group (2.84%). Regardless of treatment with iP4, the percentage of gestational loss in heifers was significantly higher (10.64%) than that in primiparous and multiparous cows (3.77% and 2.86%, respectively). The final conception rates were higher in animals that received long-acting iP4, which increased the final pregnancy in all parity categories . Discussion: In the present study, the use of iP4 increased the pregnancy rate in Nellore females, regardless of the category. Although there has been no consensus on the use of iP4, there is an agreement that increases in the pregnancy rate are related to the moment of exogenous P4 application. In addition to influencing the pregnancy rate, reduction in pregnancy losses is also attributed to iP4 treatment, a fact demonstrated in the present study, where animals treated with iP4 had a lower pregnancy loss rate than normally occurs in beef cattle. Supplementation with long-acting iP4 increased the pregnancy rate at D35-40, reduced pregnancy losses, and increased the conception rate on D80-90 days in Nellore females reared in the Western Amazon, regardless of the animal category. Keywords : abortion, reproductive biotechnologies, Bos taurus indicus , pregnancy, progesterone supplementation. Descritores: aborto, biotecnologias reprodutivas, Bos taurus indicus , gestacao, suplementacao de progesterona. Titulo: Influencia da progesterona injetavel na taxa de prenhez e perda gestacional de femeas nelore de distintas categorias reprodutivas submetidas a inseminacao artificial em tempo fixo.

Made available in DSpace on 2021-06-25T10:20:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Background: In vitro embryo production (IVEP) allows the spread of superior animal genetics, but pregnancy rates show a high variability with this biotechnique. In the initial stage of pregnancy, progesterone plays a fundamental role in uterine preparation, acting on embryonic growth, implantation, and development. However, on the day of the IVEP transfer to the recipients, progesterone levels may be lower than that expected, influencing the uterine environment and, consequently, the pregnancy rate. Therefore, the objective of this study was to evaluate the pregnancy rate in heifers after the administration of injectable progesterone (P4) in the fixed-time embryo transfer (FTET) protocol. Materials, Methods & Results: The experiment was conducted inside a rural property near the city of Rio Branco, Acre, Brazil. The experimental group consisted of 232 animals, including 78 zebuine (Bos indicus) and 154 mixed (½ blood B. indicus and ½ blood B. taurus) animals, aged between 16 and 24 months, with a mean weight of 300 and 330 kg for zebuine and mixed animals, respectively. The selected animals were previously synchronized using the progesterone-estrogen-prostaglandin-estrogen protocol. Embryo transfer was performed on day 18 of the protocol, which was 9 days after the removal of intravaginal progesterone implant. On day 15 of the protocol, that is, 144 h (6 days) after the device removal, the animals were randomly distributed into two experimental groups: Control Group (CG; 0.5 mL of 0.9% saline solution, intramuscular) and Treated Group (P4G; 0.5 mL of injectable P4, 150 mg, intramuscular). Chi-square test was used for the statistical analysis of the pregnancy rate at a 5% probability. After 23 days of embryo transfer, pregnancy was diagnosed by ultrasonography. The general pregnancy rate, considering all groups (CG and P4G) and breeds included, was 55.17% (128/232). The pregnancy rates of the P4G and CG groups, regardless of breeds, were 55.08% (65/118) and 55.26% (63/114), respectively, with no statistical difference (P = 0.8344). Angus animals presented a similar pregnancy rate in the P4G and CG groups of 54.93% (39/71) and 57.83% (48/83), respectively. Furthermore, similar results were found for the Nellore breed, with no difference in pregnancy rate between the CG (55.81%, 24/43) and P4G (48.57%, 17/35) groups. Discussion: The strategy of using P4 to increase the pregnancy rate is very widespread in fixed-time artificial insemination (FTAI) protocols, although differences still exist. The literature presents zero or negative effects, as in this study, when exogenous P4 was used to increase endogenous P4 concentrations and, consequently, the pregnancy rate. However, some studies demonstrated the beneficial effects of increasing blood P4 concentrations, and that the increased fertility depends on the method and time of P4 supplementation and the animal's physiological state. In this context, the fact that the injectable progesterone supplementation did not increase the pregnancy rate in this study is justified mainly by factors such as the animal category used (heifers), time of P4 supplementation (day 4 after ovulation), biotechnology used (FTET), and the heterogeneous characteristics related to phases of the estrous cycle of heifers. Supplementation with 150 mg of injectable long-acting progesterone intramuscularly did not interfere in the pregnancy rate of Angus and Nellore heifers receiving bovine embryos. Universidade Federal do Acre (UFAC) In Vitro Acre Empresa Especializada na Produção de Embriões Bovinos Universidade Estadual Paulista “Julio Mesquita Filho” (UNESP) Instituto Federal do Acre (IFAC) Campus Sena Madureira AC EMBRAPA Caprinos e Ovinos (CNPCO) Bolsista de Desenvolvimento Científico Regional - CNPq (DCR-CNPq/FUNCAP) Universidade Estadual Paulista “Julio Mesquita Filho” (UNESP)