Valuation of reused norgestomet implants in estrus synchronization protocols in Brahman cows

Objective. To evaluate progesterone concentrations, occurrence of estrus and pregnancy rates in Bos indicus cows submitted to several estrous synchronization protocols with previously used Norgestomet implants. Materials and methods. Sixty cows were given a reused Norgestomet ear implant on Day 0 and were assigned to receive one of four protocols: (PROT 1) estradiol benzoate (EB) + progesterone (P4) + prostaglandin F2α (PG) (EB+P4+PG); (PROT 2) estradiol valerate (EV) + norgestomet (NG) (EV+NG); (PROT 3) same as EB+P4+PG protocol, plus a 400 UI equine chorionic gonadotropin (eCG) (EB+P4+PG+eCG); (PROT 4) same as EV+NG protocol, plus a 400 UI eCG (EV+NG+eCG). The implant was removed on Day 9, with artificial insemination (AI) 12 h after detection of estrus. Pregnancy was diagnosed 45 d after AI. Blood samples were collected on Day 0, 4 and 9 (after ear implant was placed), for progesterone analysis by RIA. Results. On day 4, progesterone concentrations were lower in cows treated with EB+P4+PG (0.90 ± 0.73 ng/ml; p<0.01). Cows receiving EV+NG+eCG had greater plasma progesterone concentration (p<0.05) on Day 9 (4.72 ± 0.79 ng/ml) than other treatments. There were greater (p<0.05) percentages of estrous detection in cows treated with EV+NG+eCG (66.7%). Pregnancy rates were not affected by the treatment protocols (p>0.05). Conclusions. Reusing Norgestomet implants was effective for synchronizing estrus and promote satisfactory pregnancy rates in Brahman cows.