RESUMO

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)

Assuntos

RESUMO

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.

Assuntos

RESUMO

The objective of this study was to evaluate the effect of bovine somatotropin (bST) on ovarian follicular population in buffalo heifers and its influence on oocyte quality, recovery rates and in vitro embryo production. We tested the hypothesis that bST treatment in buffalo females submitted to an ovum pick-up (OPU) program would improve the number of follicles recruited, oocyte quality and in vitro embryo production. A total of 10 heifers were assigned into two treatment groups: group bST (n=5; receiving 500 mg of bST in regular intervals) and control group (n=5; without additional treatment). Both groups were subjected to OPU sessions twice a week (every 3 or 4 days), for a total of 10 sessions per female, although due to procedural problems, only the first five OPU sessions produced embryos. The number of follicles and the diameters were recorded at all OPU sessions. The harvested oocytes were counted and classified according to their quality as either A, B, C, D or E, with A and B considered good quality. Cleavage and blastocyst production rates were evaluated 2 and 7 days after in vitro fertilization, respectively. The bST treatment increased the total number of antral follicles (>3mm in diameter; 12.2 compared with 8.7; p<0.05) and of small antral follicles (<5mm; 9.1 compared with 6.5; p<0.05) per OPU session. The bST also tended to increase the number of oocytes recovered per session (5.2 compared with 4.1; p=0.07), and enhanced the percentage of good quality oocytes (48.8% compared with 40.6%; p=0.07). bST showed no effect on cleavage and blastocyst production rates (p>0.05). The significant effects of performing repeated OPU sessions were decreasing the follicular population (p<0.001) as well as the number of follicles aspirated (p<0.001), and oocytes recovered (p<0.02). In conclusion, bST treatment improves the follicular population, demonstrating its possible application in buffalo donors submitted to OPU programs.

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RESUMO

Induction of parturition has been used as a management tool in cattle in several countries, but not commonly in Zebu breeds in tropical production systems. When timed according to the stage of gestation, most induction protocols employing a combination of PGF2alpha and a potent, short-acting corticosteroid, resulted in a predictable interval from induction to calving, with no detrimental effects on calf viability; however, the incidence of placental retention was usually elevated. Pretreatment with a long-acting corticosteroid induced placental maturation and greatly reduced the incidence of placental retention following induction with PGF2alpha and a short-acting corticosteroid. Recently, Brazilian cattle breeders have faced a new challenge with a large number of in vitro-produced embryos. Without a reliable method of cryopreservation, large numbers of embryos have been transferred fresh, creating a new demand for protocols for synchronizing recipients and managing their calving. A parturition-induction protocol, efficacious in Bos taurus cattle, was modified for use in Bos indicus cattle (which generally have a longer gestation than B. taurus cattle). Zebu-cross recipients carrying Nelore in vitro-produced embryos were pretreated with 1 mg/60 kg triamcinolone acetonide on Day 280 of gestation, followed by treatment with 500 microg of cloprostenol and 25 mg of dexamethasone on Day 287. The interval from treatment to calving was predictable and the incidence of retained placenta was low, similar to that described previously for B. taurus cattle, demonstrating that this treatment protocol could be used for induction of parturition in Zebu cattle in Brazil.

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RESUMO

The objective was to evaluate the effects of 400 IU of eCG given on Days 5 or 8 of an estrus synchronization protocol with progesterone-releasing intravaginal devices (PRID) and estradiol benzoate (EB), in recipients for fixed-time embryo transfer. A secondary objective was to determine the effects of injectable progesterone (given concurrent with EB treatment). Three-hundred-and-four crossbred Bos taurus x Bos indicus beef heifers were randomly assigned to one of four treatment groups (2 x 2 factorial design). At unknown stages of the estrous cycle (Day 0), all heifers received a progesterone-releasing intravaginal device (PRID), plus 2mg of EB i.m., with or without a concurrent treatment of 50mg of progesterone i.m. Heifers were further subdivided to receive 0.15 mg of d-cloprostenol (PGF) i.m. and 400 IU of eCG i.m. on Days 5 or 8. In all heifers, intravaginal devices were removed on Day 8 and 1mg of EB was given i.m. on Day 9 (Day 10 was arbitrarily considered the day of estrus). On Day 17, all heifers with >1 CL or a single CL with a diameter > or =18 mm (based on ultrasonographic examination), received an in vitro produced (IVP) embryo by non-surgical transfer. On Day 17, there was an effect of day of eCG administration on the number of CL (1.35 +/- 0.08 versus 1.13 +/- 0.04, for Day 5 versus Day 8, respectively; P = 0.02) and (in a subset of 154 heifers) mean (+/-S.E.M.) plasma progesterone concentrations (2.41 +/- 0.26 versus 1.74 +/- 0.19 ng/mL; P = 0.03). Although the proportion of recipients transferred/treated and pregnant/transferred did not differ among groups, the proportion of recipients pregnant/treated tended (P = 0.1) to be higher in heifers treated with eCG on Day 5 versus Day 8 (47.0% versus 40.7%, respectively). Progesterone treatment had no significant effect. In conclusion, treatment with eCG (and D-cloprostenol) on Day 5 significantly increased the number of CL and plasma progesterone concentrations and tended to increase pregnancy rates, although progesterone treatment had no significant effect.

Assuntos

RESUMO

Most of the world's bovine herd is found in tropical regions. Bos indicus predominates, due to their adaptation to the climate and management conditions. Anestrous is the main factor that negatively affects reproductive performance of animals bred in these regions of the globe. Several factors affect postpartum anestrous, including suckling and maternal-offspring bond, and pre- and postpartum nutritional status. The short duration of estrus and the tendency to show estrus during the night, greatly affect the efficiency of artificial insemination (AI) programs in B. indicus cattle managed in tropical areas. Several restricted suckling or weaning procedures (temporary or permanent), and hormonal treatments have been used to induce ovulation and cyclicity in postpartum cows. Most hormonal treatments are based on progesterone/progestogen (P4) releasing devices associated with estradiol benzoate (EB), or a combination of GnRH/PGF(2alpha)/GnRH (Ovsynch). Treatments with GnRH/PGF(2alpha)/GnRH has presented inconsistent results, probably due to the variable number of cows in anestrous. Treatments using P4 devices and EB have resulted in apparently more consistent results than Ovsynch programs in B. indicus cattle; however, pregnancy rates are low in herds presenting high anestrous rates and moderate to low body condition. The addition of an eCG treatment at the time of device removal, which increased plasma progesterone concentrations and pregnancy rates in anestrous postpartum suckled B. indicus cows, may be useful to improve reproductive performance of beef cattle in tropical climates.

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Assuntos