Impact of 17β-estradiol addition at the moment of timed-AI in Nelore cows

• Ano de defesa: 2023
• Autor(a) principal: Bisinotto, Danilo Zago
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Dominant follicle; Estradiol; Folículo dominante; Inseminação artificial em tempo fixo; Modulação uterina; Timed artificial insemination; Uterus modulation
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/10/10131/tde-08122023-171851/

This study aimed to evaluate the effects of administering estradiol (E-17β) at the time of TAI on uterine gene expression, estrous expression rate (EER), and pregnancy rate (P/TAI) in Nelore cows with a small dominant follicle (DF) or not showing estrus until the time of TAI. In Experiments 1 and 2, non-lactating cows were submitted to a P4/ E-17β -based protocol for starting at early diestrus (D0). On D7, 12.5mg dinoprost tromethamine and 1mg E-17β cypionate were injected. On D9, cows with DF<11.5 mm were assigned to different experimental groups. In Exp1 (n=16/group): Control (C, no treatment), E-2 (i.m., 2mg E-17β) and E-4 (.i.m, 4mg E-17β); whereas in Exp2: C (no treatment; n=12); E-2 (2mg E-17β, n=14); GnRH (0.1mg gonadorelin acetate, n=13); and E-2+GnRH (association of GnRH and E- 17β, n=13). In both experiments, between D9 and D11 cows were submitted to transrectal ultrasonography every 12 (Exp1) or 6 (Exp2) hours (h) for ovulation detection, determination of endometrial thickness (ET), and a patch was fitted halfway between the hip and tail head for EER. In Exp1, a uterine cytological sample was collected 4h after treatment to evaluate the transcript expression of receptors for E-17β (E2R), oxytocin (OXTR), and P4 (PGR). In Exp3, 3,829 suckled cows with a BCS of 2.9 (scale 1 to 5) were submitted to a TAI. On D0, cows received a P4- device (0.6g) and 2mg E-17β benzoate. On D9, devices were removed and cows received 300IU eCG, 0.39mg sodium cloprostenol, 1mg E-17β cypionate, and a marker stick at the base of the tail for EER. On D11, TAI was performed and cows that did not demonstrate estrus had the DF diameter determined, received 0.1mg gonadorelin acetate, and were allocated into two groups: GnRH (n=368) and E- 2+GnRH (2mg E-17β; n=363). In Exp1, data were separated by orthogonal contrasts (C1; C vs. E-17β; and C2: E-2 vs. E-4) and Exp2 in a 2x2 factorial. Variables were evaluated by ANOVA or logistic regression using SAS software. In Exp1, ET was reduced (P<0.05) 12h after treatment in E-17β-treated cows. The E-17β-treated cows had greater (P<0.05) transcript abundance for OXTR and lesser (P<0.05) for ESR1 and ESR2. For C2 contrast, no significant difference (P>0.1) was observed. In Exp2, the EER did not differ (P>0.1), but the interval from treatment to ovulation (h) was longer (P<0.05) in cows from the E-17β (40±1.6) compared to others (C: 31±2; GnRH: 28±0.9; E-2+GnRH: 29±0.1). When evaluating ovulation rates, there was an effect of both GnRH (P>0.01), where treated groups showed higher ovulation rates (88.9%) when compared to untreated groups (35.4%), as groups that received E-17β (P>0.01) had a lower rate (43.9%) when compared to those that did not receive it (77.8%), up to 36 hours. In Exp3, the P/TAI was 55% for cows in estrus. For those not showing estrus, no difference (P>0.1) in pregnancy rate was observed between GnRH (34%) and E-2+GnRH (31%) groups. Regardless of the E-17β- treatment, cows with a DF≥11 mm (n=192) had a greater (P<0.05) P/TAI (49%) than those with DF<11 mm (n=377; 29%). In conclusion, E-17β administration in the moment of TAI modulates the mRNA expression of uterine receptors in cows with a small DF but does not impact the P/TAI compared with GnRH treatment in suckled Nelore not showing estrus previous to TAI.