Efeito do intervalo entre a inseminação e a ovulação na taxa de concepção de vacas Nelore inseminadas em tempo fixo com sêmen sexado

Abstract

NEVES, K. A. L. Effect of interval between insemination and ovulation in conception rates in Nelore cows timed AI with sex-sorted semen. [Efeito do intervalo entre a inseminacao e a ovulacao na taxa de concepcao de vacas Nelore inseminadas em tempo fixo com semen sexado]. 2010. 89f. Dissertacao (Mestrado em Ciencias) – Faculdade de Medicina Veterinaria e Zootecnia, Universidade de Sao Paulo, Sao Paulo, 2010. The identification of most appropriate moment to perform the timed artificial insemination (TAI) using sex-sorted semen following synchronization protocol can be important to improve the fertility of sex-sorted semen and increase the use sexed semen technology in commercial beef farms. The aim of this study was evaluated the better interval to perform the TAI relative to synchronized ovulation in suckled cows. A total of 339 suckled multiparous Nelore cows from an experimental farm (APTA), in Colina-SP, were evaluated in this study. The protocol started between 30 and 60 days post-partum. Cows received one synchronization protocol using an intravaginal device containing 1.0g of progesterone (Sincrogest, Ouro Fino) plus an i.m. injection of 2.0mg of EB (Sincrodiol, Ouro Fino). Eight days later, the device was removed and 0.25mg i.m. injection of cloprostenol sodium (Sincrocio, Ouro Fino) and 300IU of eCG (Folligon, Intervet-Shering Plough) were administered. Cows were homogenously assigned to receive TAI using sex-sorted semen from a single sire (2.1 millions of sperm cell per straw) at 36, 48 or 60 hours after device removal. The TAI to ovulation interval of synchronized cows was determined and the analysis was performed to compare the pregnancy for TAI performed at various intervals before ovulation using 12 hours time intervals. Ovarian ultrasonographic examinations (CTS-3300V, SIUI, China) were performed twice daily from day of the device removal to 96 hours afterwards, to evaluate ovarian follicular dynamics and interval from device removal to ovulation. All females were examined for pregnancy 30 days after AI. The data were analyzed using the SAS program.Incidence of ovulation after the estrous synchronization protocol was 92.0 % (312/339). Diameter of ovulatory follicle was 14.7 ± 2.3 mm and the interval between the P4 device removal and synchronized ovulation occurrence was 71.8 ± 7.7 hours. The distribution of the synchronized ovulation relative to the device removal was: 48 hours (6.73%; 21/312), 60 hours (0.64%; 2/312), 72 hours (80.77%; 252/312), 84 hours (11.22%; 35/312), and 96 hours (0.64%; 2/312). The pregnancy per artificial insemination (P/AI) was increased (P 24 hours (5.8%; 5/87; P = 0.0001) before the synchronized ovulation. Recently ovulated cows had P/AI similar to those performed around the time of ovulation (36,4%; 8/22). In conclusion, P/AI is increased when the TAI using sex-sorted is performed closer to synchronized ovulation in suckled Nelore cows. In experiment 2, resynchronization, were assessed the service rates, conception and pregnancy in cows previously synchronized and timed AI. Two groups were formed: estrous detection and TAI, using in AI, sexed and unsexed semen. The results for groups of estrus detection and TAI were, respectively, service rate [(63.5% (61/96) 100% (88/88)], conception rate [(41% (25/61), 11.4% (10/88))], pregnancy rate [(26% (25/96), 11.4% (10/88))]. The results for groups of estrus detection and TAI according the type of semen used were: conventional semen conception rate [(43.3% (13/30), 14.9% (7 / 47))] ; pregnancy rate [(27.49% (13/61), 14.9% (7 / 47))]; sexed semen conception rate [(38.7% (12/31) 7.3% (3 / 41))]; pregnancy rate [(24.57% (12/ 61), 7.3% (3 / 41))].