Reduced-dose norgestomet ear implant for estrous synchronization in santa inês ewes undergoing fixed-time artificial insemination

Resumo

The present study evaluated the reproductive performance of a reduced-dose norgestomet ear implant as an alternative to a conventional medroxyprogesterone acetate (MAP) intravaginal sponge for estrous synchronization in Santa Inês ewes submitted to fixed-time artificial insemination (FTAI). Thirty-five clinically healthy, non-lactating ewes were randomly assigned to two synchronization protocols: one-third of a commercial 3 mg norgestomet ear implant (approximately 1 mg of norgestomet) (n = 18) or a 50 mg MAP intravaginal sponge (n = 17), both maintained for 14 days. At device removal, all ewes received 200 IU equine chorionic gonadotropin (eCG), and FTAI was performed 56 h later using chilled semen. Pregnancy was diagnosed by transabdominal ultrasonography 45 days after insemination. Pregnancy rates were 50.0% (9/18) in the norgestomet group and 35.3% (6/17) in the MAP group, with no significant difference between treatments (Fisher's exact test, P = 0.51). No premature device losses occurred in either group. Mild vaginal discharge was observed after removal of MAP sponges, whereas ewes treated with the ear implant showed only slight transient swelling at the insertion site. These findings indicate that a reduced-dose norgestomet ear implant is as effective as a conventional MAP sponge for estrous synchronization in Santa Inês ewes undergoing FTAI. In addition to comparable reproductive performance, the ear implant offers practical advantages by avoiding direct contact with the vaginal mucosa, which may reduce local alterations associated with intravaginal devices and, based on previous studies, presents potential for reuse after appropriate sanitation, which may improve its cost-effectiveness under field conditions.