estradiol valerate and 3.0 mg norgestomet (EVþN) on the first day of the treatment. Nine days later, the ear implant was withdrawn and cows were given 400 IU
eCG. Cows were bred by TAI 52 to 56 hours after ear implant removal and concurrently given 100 ug of GnRH. Cows from the TAIþNS group received TAI on Day
11 of the BS, followed by NS until the end of the BS; TAIþEDþNS: cows in the TAIþEDþNS received TAI on Day 11, then were observed for estrus twice a day with
AI 12 hours after ED until Day 45 of the BS, followed by NS until the end of BS; EDþNS: cows were artificially inseminated after estrous detection during the first
45 days of the BS followed by NS until the end of the BS; NS: breeding was exclusively by NS throughout the entire BS. BS, breeding season; ED, estrus detection;
NS, natural service; TAI, timed AI.