Fixed-time artificial insemination with estradiol and progesterone for Bos indicus cows I: basis for development of protocols.

Five experiments were conducted on commercial farms in Brazil aiming to develop a fixed-time artificial insemination (TAI) protocol that achieved pregnancy rates between 40% and 55% in Bos indicus cows. These studies resulted in the development of the following protocol: insertion of an intravaginal device containing 1.9 g of progesterone (CIDR) plus 2.0mg im estradiol benzoate on Day 0; 12.5mg im dinoprost tromethamine on Day 7 in cycling cows or on Day 9 in anestrous cows; CIDR withdrawal plus 0.5mg im estradiol cypionate plus temporary calf removal on Day 9; TAI (48h after CIDR withdrawal) plus reuniting of calves with their dams on Day 11. Reduced dose of prostaglandin F(2alpha) (PGF(2alpha); 12.5mg im dinoprost tromethamine) effectively caused luteolysis. In cycling cows, fertility was greater when the treatment with PGF(2alpha) was administered on Day 7 than on Day 9, but in anestrous cows, no effects of time of the PGF(2alpha) treatment were found. Estradiol cypionate effectively replaced estradiol benzoate or gonadotropin-releasing hormone as the ovulatory stimulus, reducing labor and cost. In this protocol, CIDR inserts were successfully used four times (9 d each use) with no detrimental effects on fertility.