Autor(es)

Consentini, Carlos E. C. ; Melo, Leonardo F. ; Abadia, Tattiany ; Gonzales, Bruno ; Motta, Jessica C. L. ; Alves, Rodrigo L. O. R. ; Silva, Lucas O. e ; Wiltbank, Milo C. ; Sartori, Roberto

• Tipo de documento: Artigo Científico
• Fonte: JOURNAL OF DAIRY SCIENCE; v. 107, n. 7, p. 10-pg., 2024-06-26.

Resumo

The present study compared 2 strategies to initiate a progesterone (P4) -based timed artificial insemination (TAI) protocol for lactating dairy cows: only GnRH or estradiol benzoate (EB) plus GnRH (EB+GnRH). Lactating Holstein cows (n = 487; 184 primiparous and 303 multiparous) from 2 commercial dairy herds were used for their second or greater services postpartum. Each week, cows that were nonpregnant at the pregnancy diagnosis 32 d after a previous AI were randomly assigned to 1 of 2 experimental groups that differed only in the strategy to initiate (d 0) the TAI protocol. On d 0, every cow received a 2.0-g P4 implant; in the EB+GnRH group, cows were treated with 2.0 mg i.m. of EB and 16.8 mu g i.m. of the GnRH analog buserelin acetate, whereas in the GnRH group, cows received only 16.8 mu g i.m. of GnRH. On d 7 after the initial treatment, 0.530 mg i.m. of cloprostenol sodium (PGF) was administered in all cows, followed by a second dose on d 8, concomitant with 1.0 mg i.m. of estradiol cypionate and P4 implant withdrawal. The TAI was performed on d 10 (48 h after P4 device withdrawal) in both experimental groups. Only conventional Holstein semen was used throughout the study. The percentage of cows with corpus luteum (CL) on d 0 (73%) and overall ovulation rate after d 0 (54%) did not differ between groups. The CL regression between d 0 and the first PGF treatment was greater in the EB+GnRH group than the GnRH group (42% vs. 31%). Consequently, the proportion of cows with CL at PGF was greater when only GnRH was used on d 0 compared with EB+GnRH (86% vs. 82%), and the mean number of CL at PGF was greater (1.23 vs. 1.11). The expression of estrus near TAI was greater in GnRH group (84% vs. 77%), and cows showing estrus had greater (44% vs. 10%) pregnancy per AI (P/AI) on d 32 for both treatments. We found no effect of the presence of CL on d 0 or at PGF, nor of ovulation after d 0 or CL regression between d 0 and d 7 on fertility. However, fertility was critically impaired when cows did not have CL at both times, d 0 and at PGF treatment. We did not observe any interaction between treatment and other variables, and the P/AI was similar in cows receiving EB+GnRH or only GnRH on d 0 (37.8% vs. 36.6%). In summary, although there was no detectable difference in P/AI between treatments, this study demonstrated potential negative physiological outcomes caused by EB treatment on d 0 (greater incidence of luteolysis after d 0 and fewer cows with CL at PGF treatment). Overall, we found no benefit of adding EB at the initiation of a P4 -based TAI protocol on fertility compared with using GnRH alone, despite differences in ovarian dynamics and expression of estrus. (AU)

• Processo FAPESP: 17/15904-3 - Programas inovadores de pré-sincronização, sincronização e ressincronização para IATF em vacas leiteiras
• Beneficiário: Carlos Eduardo Cardoso Consentini
• Modalidade de apoio: Bolsas no Brasil - Mestrado
• Processo FAPESP: 18/03798-7 - Estudos de fisiologia ovariana e uterina e aprimoramento de Tecnologias de Reprodução Assistida para elevar a eficiência reprodutiva em bovinos
• Beneficiário: Roberto Sartori Filho
• Modalidade de apoio: Auxílio à Pesquisa - Temático