Sistema para inseminação artificial sem observação de estro em vacas de corte amamentando

O objetivo deste estudo foi desenvolver um protocolo de inseminacao artificial com tempo fixo (IATF) em vacas de corte amamentando, avaliando o intervalo entre a retirada do progestageno e a aplicacao de GnRH sobre a dinâmica folicular e a prenhez. Para isto, 227 vacas 60-80 dias pos-parto receberam benzoato de estradiol (5mg) e um pessario vaginal de acetato de medroxiprogesterona (250mg MAP; dia 0). No dia seis, cloprostenol sodico (125μg), gonadotrofina corionica equina (400UI) e desmame temporario (88h). O MAP foi retirado no dia sete (Grupo BioRep) ou no dia oito (Grupo IATF) e, 48h ou 24h apos os animais receberam GnRH (100μg; dia 9), respectivamente. No experimento I, o monitoramento das estruturas ovarianas de 14 vacas foi realizado a cada 24h, desde o dia seis ate 36h apos a aplicacao de GnRH em ambos os grupos. O tamanho medio do foliculo dominante no dia nove foi de 11,10,99mm (BioRep n=7) e 11,50,65mm (IATF n=7) e todos os animais ovularam. No experimento II, no grupo BioRep (n=106), apos a retirada do MAP, as femeas foram inseminadas com deteccao de estro durante 48 horas. O restante dos animais do grupo BioRep e todos do grupo IATF (n=107) receberam 100μg de GnRH (dia 9) e, apos 16h, IATF. Os indices de prenhez foram de 57,6% (BioRep) e de 52,3% (IATF). O intervalo de 24h entre a retirada do MAP, mantido por 8 dias, e a aplicacao de GnRH nao interfere na dinâmica folicular e prenhez, viabilizando inseminar vacas de corte amamentando sem observacao de estro.%%%%The aim of this study was to develop a timed artificial insemination system (TAI) in suckled beef cows. For this, in 227 cows 60-80 days postpartum, received estradiol benzoate (5mg) and a vaginal device containing 250mg of medroxyprogesterone acetate (MAP; day 0). On day six, prostaglandin analogous (125μg), eCG (400IU) was administered and calves were removed for 88h. The device was removed on day seven (BioRep group) or on day eight (TAI group) and the cows of both groups received GnRH (100μg; day 9) 48h or 24h after device withdrawal, respectively. Experiment I: the follicular growth was daily monitored, from day 6 to day 9 (36h after GnRH), in 14 cows. The average of dominant follicle size on day nine was 11.10.99mm (BioRep, n=7) and 11.50.65mm (TAI, n=7) and all animals ovulated. Experiment II: in the BioRep group (n=106), the cows was observed for estrus behavior after withdrawal the device, twice a day during 48h and inseminated at 12h after detection; In the TAI group (n=107), the devices were withdrawn on day eight and after 24h these cows and those from the BioRep group, which were not stand in estrus, received 100μg of GnRH and TAI 16h later. The pregnancy rates were 57.6% (BioRep) and 52.3% (TAI). The time of MAP exposure and the period from MAP to GnRH did not affect the follicular dynamic and pregnancy rates. Furthermore, the treatment for eight days allows an efficient TAI system in suckled beef cows.