RESUMO
Two experiments were conducted to assess a hormonal strategy developed to reduce animal handling for timed artificial insemination (TAI) with sex-sorted semen. Four-hundred ninety-one (491) suckled beef cows received a progesterone (P4) intravaginal device and 2â¯mg intramuscular (im) injection of estradiol benzoate (EB) on a randomly chosen day of the estrus cycle (Day 0) in Experiment 1. Cows were treated with 500⯵g of sodic cloprostenol (PGF2α) and with 300 IU of eCG at P4 device removal (Day 8); these cows were also randomly assigned to receive 1â¯mg of estradiol cypionate (EC) administered at P4 device removal (treatment EC-0h) or 1â¯mg of EB 24â¯h after P4 device removal (treatment EB-24h). Both treatments were timed inseminated (TAI) with sex-sorted semen 60â¯h after P4 device removal. Cows treated with EC-0h presented higher pregnancy rate per AI (P/AI) [45.0% (113/251)] than the ones treated with EB-24h [35.4% (85/240); Pâ¯=â¯0.03)]. A subset of cows (nâ¯=â¯26) were subjected to ultrasound examination every 12â¯h after P4 device removal for 96â¯h in the row in order to determine the time of ovulation. Similar interval between device removal and ovulation was recorded for EB-24hâ¯=â¯70.0⯱â¯2.9â¯h vs. EC-0hâ¯=â¯66.0⯱â¯2.8â¯hâ¯(Pâ¯=â¯0.52). Five-hundred ninety-one (591) cows were subjected to the same synchronization protocols and treatments (EC-0h or EB-24h). In addition, they were randomly assigned to a 2â¯×â¯2 factorial arrangement aiming at determining the effects of treatment with estradiol (EC-0h vs. EB-24h) and of semen type (Sex-sorted vs. Non-sex-sorted semen). All animals were timed inseminated 60â¯h after P4 device removal. There was no interaction (Pâ¯=â¯0.07) between the ovulation inducer and semen type. The EC protocol led to greater P/AI than EB (Pâ¯=â¯0.03). Greater (Pâ¯=â¯0.01) P/AI was achieved through treatments with non-sex-sorted semen rather than with sex-sorted semen [sex-sorted (EB-24hâ¯=â¯49.0%; EC-0hâ¯=â¯51.0%) vs. non-sex-sorted semen (EB-24hâ¯=â¯52.4%; EC-0hâ¯=â¯68.2%)]. Therefore, EC administered at P4 device removal resulted in greater P/AI. Furthermore, the EC-0h protocol allowed reducing suckled beef cow handing for timed artificial insemination with sex-sorted semen.