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      Efecto de la Dosis de eCG sobre las Características Foliculares y Luteales, momento y Tasa de Ovulación de Novillas Mestizas Cebú Sincronizadas con Progestágeno Intravaginal Translated title: Effect of the eCG Dose on Follicular and Luteal Characteristics, Ovulation Time and Ovulation Rate of Crossbred Zebu Heifers Synchronized with an Intravaginal Progestagen Device

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          Abstract

          Para evaluar el efecto de una dosis reducida de la gonadotropina coriónica equina (eCG) sobre el crecimiento folicular, las características luteales, el momento de la ovulación y la tasa de ovulación en novillas mestizas cebú sincronizadas con un progestágeno intravaginal, se seleccionaron 41 novillas cíclicas. Para la sincronización se utilizó una esponja intravaginal (EI) impregnada con 250 mg de medroxi-acetato-progesterona (MAP), bajo el protocolo siguiente: Día 0: Inserción de la EI más 2 mg de benzoato de estradiol (BE) im y 25 mg de PGF2a im; Día 6: 12,5 mg de PGF2a, 21 novillas recibieron 400 UI de eCG im (T1; n=21) y 20 recibieron 200 UI (T2; n=20); Día 8: retiro de EI; Día 9: 0,5 mg de BE im. La evaluación ultrasonográfica se realizó entre los días 6 y 8, cada 24 h, para determinar la tasa de crecimiento folicular (TCF). A partir del día 8 hasta la ovulación, se evaluaron cada 8 h para determinar el diámetro del folículo ovulatorio (DFO), el momento de la ovulación (MO), el diámetro y área del cuerpo lúteo (DCL y ACL), así como la tasa de ovulación (TO). Las variables TCF, DFO, DCL y ACL se analizaron con el PROC GLM, mientras que el MO mediante el procedimiento NPAR1WAY y la TO mediantec2, utilizando el PROC FREQ del SAS. No hubo diferencias en las variables TCF, DFO y ACL (1,44±0,27 vs.1,72±0,27 mm/d; 12,61±0,47 vs.13,85±0,47 mm y 33,9±2,1 vs. 30,3±2,4 mm² para T1 y T2, respectivamente). Las ovulaciones ocurrieron en promedio 61,67±1,8 y 62,73±1,92 h, respectivamente después de retirado el dispositivo para T1 y T2. El DCL fue mayor (P<0,05) en T1 que en T2 (21,7±1,44 vs.16,9±1,56 mm). Se encontraron mayores porcentajes para la TO (P=0,06) en el grupo T1 que en T2 (95,25 vs. 75%). En conclusión, la dosis de 200 UI de eCG fue suficiente para inducir un adecuado crecimiento folicular y no afectar el momento de la ovulación y la dosis de 400 UI de eCG mejoró las características del cuerpo lúteo y permitió obtener un mayor número de ovulaciones en novillas mestizas cebú sincronizadas con un progestágeno intravaginal.

          Translated abstract

          The effect of a reduced dose of eCG on follicular growth, luteal characteristics, ovulation time (OT) and ovulation rate (OR) was evaluated in crossbred Zebu heifers synchronized with an intravaginal progestagen device. A total of 41 cyclic heifers was selected and synchronized with an intravaginal sponge (IE) impregnated with 250 mg of medroxy-progesterone-acetate (MPA), using the following protocol. Day 0: insertion of IE plus 2 mg of estradiol benzoate (EB) im and 25 mg of PGF2a im. Day 6: 12.5 mg de PGF2a, 21 heifers received 400 IU eCG im (T1; n = 21) and 20 received 200 IU (T2; n = 20). Day 8: IE withdrawal. Day 9: 0.5 mg of BE im. Heifers were timed-artificial inseminated (TAI) between 52 and 56 h after IE withdrawal. Ultrasound evaluation was performed between d 6 until d 8, every 24 h, to determine the rate of follicular growth (FGR). Then, from d 8 until ovulation, heifers were evaluated every 8 h to determine diameter of the ovulatory follicle (DOF), OT, and diameter (CLD) and area (CLA) of the corpus luteum. The OR was also assessed. The variables FGR, DOF, CLD and CLA were analyzed using PROC GLM, while OT was analyzed using the NPAR1WAY procedure and OR using Chi-square with PROC FREQ from SAS. No differences were found in FGR, DOF, and CLA (1.44±0.27 vs. 1.72±0.27 mm/d; 12.61±0.47 vs. 13.85±0.47 mm and 33.9±2.1 vs. 30.3±2.4 mm² for T1 and T2, respectively). Ovulations occurred at 61.67±1.8 h and 62.73±1.92 h, respectively, after IE withdrawal for T1 y T2, respectively. The CLD in T1 was higher (P<0.05) than T2 (21.7±1.44 vs. 16.9±1.56 mm). Higher OR (P=0.06) were found in T1 than in T2 (95.25 vs. 75.0%). In conclusion, the dose of 200 IU of eCG was sufficient to induce an suitable follicular growth without affecting OT and dosing with 400 IU of eCG improved the corpus luteum characteristics and allowed to obtain a greater number of ovulations in crossbred Zebu heifers synchronized with an intravaginal progestagen.

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          Equine chorionic gonadotropin.

          Cells from the chorionic girdle of the equine trophoblast invade the maternal endometrium at day 36 of gestation and become established as secretory elements known as the endometrial cups. These structures, which persist for 40-60 days, produce a gonadotropin which can be found in circulation until about day 130 of gestation. This glycoprotein has been identified in the horse and the donkey, with the former having received much better characterization. It consists of 2 noncovalently linked peptide chains; an alpha-subunit of 96 amino acids, which is common to that found in other horse glycoprotein hormones. The beta-subunit of 149 amino acids is identical to horse LH beta. Horse CG is the most heavily glycosylated of the known pituitary and placental glycoprotein hormones. The alpha-subunit has two and the beta-subunit one N-linked glycosylation site, and the beta-chain has in excess of four O-linked glycosylation sites. The N-linked glycans have some oligosaccharides that are not found on other glycoprotein hormones. The sialic component of glycosylation confers an exceptionally long half-life on CG compared to other glycoprotein hormones. Horse CG has LH-like activity in horse receptor and in vitro bioassays. In spite of the amino acid homology, it has lower LH activity than does horse LH. Its most intriguing, and as yet unexplained, characteristic is its pronounced FSH and LH activity in species other than the horse. Horse CG binds to FSH receptors of virtually all mammalian species, other than the horse, in which it has been tested and will produce biological effects peculiar to FSH. It has similar and potent interaction with LH receptors. The structural basis of this duality is not known but may be related to the region 90-110 of the beta-chain. Horse CG is believed to be constitutively expressed by the trophoblastic cells until the endometrial cups degenerate. The role of CG in equine gestation is not completely understood. It is believed to act as an LH-like hormone to induce supplementary ovulation and/or luteinization of follicles in the mare. It has not been established whether CG or the accessory corpora lutea are necessary for successful horse pregnancy. They may serve as a redundant system to assure that there is sufficient secretion of the primary corpus luteum to maintain pregnancy until the placenta assumes its role as the principal steroidogenic organ of gestation.
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            Manipulation of follicle development to ensure optimal oocyte quality and conception rates in cattle.

            Over the last several decades, a number of therapies have been developed that manipulate ovarian follicle growth to improve oocyte quality and conception rates in cattle. Various strategies have been proposed to improve the responses to reproductive biotechnologies following timed artificial insemination (TAI), superovulation (SOV) or ovum pickup (OPU) programmes. During TAI protocols, final follicular growth and size of the ovulatory follicle are key factors that may significantly influence oocyte quality, ovulation, the uterine environment and consequently pregnancy outcomes. Progesterone concentrations during SOV protocols influence follicular growth, oocyte quality and embryo quality; therefore, several adjustments to SOV protocols have been proposed depending on the animal category and breed. In addition, the success of in vitro embryo production is directly related to the number and quality of cumulus oocyte complexes harvested by OPU. Control of follicle development has a significant impact on the OPU outcome. This article discusses a number of key points related to the manipulation of ovarian follicular growth to maximize oocyte quality and improve conception rates following TAI and embryo transfer of in vivo- and in vitro-derived embryos in cattle.
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              Fixed-time AI protocols replacing eCG with a single dose of FSH were less effective in stimulating follicular growth, ovulation, and fertility in suckled-anestrus Nelore beef cows.

              The aim of the present study was to evaluate the effects of a single treatment with FSH on diameter of the largest follicle and on conception rates of suckled Bos indicus beef cows submitted to timed artificial insemination (TAI). Four hundred fifty-six suckled anestrous Nelore beef cows at 30-60 days postpartum were assigned to treatments. At the first day of the estrous synchronization protocol (Day 0), all cows received a progesterone-releasing intravaginal device plus 2mg of estradiol benzoate. On Day 8, cows were assigned to blocks according to the diameter of the largest follicle and then allocated to one of three treatment groups (Control, FSH, or eCG) within each block. Simultaneously to progesterone device withdrawal on Day 8, cows in the eCG treatment group (n=150) received 300 IU of eCG and cows in FSH treatment group (n=153) received 10mg of FSH, and Control cows (n=153) did not receive any additional treatment. Additional treatments with 150 μg of cloprostenol and 1mg of estradiol cypionate (EC) were also administered concurrently to progesterone device removal in all cows on Day 8. Two days later (D10), TAI and ovarian ultrasonic examinations to evaluate follicle size were performed in all cows. On Day 12, a subset of cows (n=389) were submitted a second ultrasonic exam to confirm ovulation. Final follicular growth (mm/day) was less (P=0.006) in both Control (0.95±0.11) and in FSH-treated cows (0.90±0.10) than in eCG-treated cows (1.40±0.13). Interestingly, there was a treatment-by-BCS interaction in ovulation results (P=0.03), in which, eCG treatment increased percentage of cows having ovulations with a lesser BCS. Similarly, there was a treatment-by-BCS interaction for conception (P=0.04), where the eCG treatment increased fertility in cows with a lesser BCS. In conclusion, FSH failed to stimulate final follicular growth, ovulation, and conception rate in sucked-anestrous beef cows submitted to TAI as effectively as eCG. However, physiological effects of eCG seem to be more evident in cows with a lesser BCS.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                rfcv
                Revista de la Facultad de Ciencias Veterinarias
                Rev. Fac. Cienc. Vet.
                Revista de la Facultad de Ciencias Veterinarias. Universidad Central de Venezuela.
                0258-6576
                2015
                : 56
                : 1
                : 035-041
                Affiliations
                [1 ] Universidad del Zulia Venezuela
                Article
                S0258-65762015000100005
                44893ef3-e731-40fb-86b7-33a4d3b47caf

                http://creativecommons.org/licenses/by/4.0/

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                Product

                SciELO Venezuela

                Self URI (journal page): http://www.scielo.org.ve/scielo.php?script=sci_serial&pid=0258-6576&lng=en
                Categories
                AGRICULTURE, DAIRY & ANIMAL SCIENCE
                VETERINARY SCIENCES

                Animal agriculture,General veterinary medicine
                Animal agriculture, General veterinary medicine

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