The percentage of estrus induction and plasma LH concentrations were examined in 15 Azawak zebu cows submitted to two different estrus synchronization protocols. In the first treatment (T1, n = 9), the cows received a norgestomet ear-implant for 10 days associated with estradiol valerate, prostaglandin F2alpha (PGF2alpha) and pregnant mare serum gonadotropin (PMSG) injections. Treatment 2 (T2, n = 6) consisted in two PGF2alpha injections 11 days apart, followed by the administration of PMSG two days after the second prostaglandin injection. Blood samples were collected every three hours during five days after implant removal (T1) or PMSG injection (T2) for LH measurements. The proportion of induced estrus was higher in T2, but the difference was not significant. In general, the elapsed time until the estrus onset tended to be shorter in norgestomet-treated animals (35.9 ± 3.9 h) than in prostaglandin-treated ones (49.5 ± 5.8 h). Seven out of nine norgestomet-treated cows, and only two out of the six treated with PGF2alpha, presented a peak of LH. The mean interval from the end of treatments to LH peak tended to be longer in PGF2-treated females than in norgestomet-treated ones. One female presenting abnormally high LH concentrations after implant removal did not show a peak of LH during the observation period
