A total of 48 repeat breeder cows were equally divided in to two treatment groups as NOR and NOR-PG and were treated with norgestomet ear implants on day 10 following natural oestrus and a control group. At the time of ear implant insertion, 2 ml of SMB injection was administered intramuscularly to all the cows. The implant was removed after 9 days. Cows in NOR-PG group were injected with 0.98 mg of PGF2a at the time of implant removal. In NOR and NOR-PG groups, AI was done at 48 and 72 hours of implant withdrawal. In control group, cows were artificially inseminated twice at 24 hours interval during natural oestrus. Blood samples were collected at the time of implant insertion and withdrawal in all the treated cows for progesterone assay. There was 100 per cent oestrus response following implant removal in NOR and NOR-PG groups. The conception rate obtain in NOR, NOR-PG and control groups were 43.75, 37.50 and 18.75 per cent, respectively. The overall mean level of progesterone (6.31±0.32 ng/ml) noticed at the time of implant insertion was significantly reduced to a lower level (1.38±0.16 ng/ml) by the time of its removal in treated cows. It is inferred that norgestometâ€“oestradiol alone without PGF2a may be used to augment fertility in repeat breeder cows under field conditions.
PGF2 alpha, Oestrus, Norgestomet, Oestradiol, Fertility Rate, Repeat Breeder Cows.