Comparison of two progesterone formulations in an ovulation induction protocol with fixed-time artificial insemination in beef cows in postpartum anestrus

Abstract

Three trials were conducted to compare a natural, injectable, progesterone (MAD-4) with an intravaginal device (DIV). The protocol used was: Day 0: 2 mg of estradiol benzoate (BE) i/m plus 320 (trial 1) or 200 (trials 2 and 3) mg of MAD-4 s/c or insertion of a DIV; Day 7: 0.15 mg of D-Cloprostenol (PG) i/m plus 400 IU of eCG i/m and withdrawal of the DIV; Day 9: 8 µg Buserelin acetate (GnRH) i/m; Day 10: FTAI. The pregnancy rate (PR) to the ultrasound performed 30 days after the FTAI were: 31.6% in trial 1, 13.5% in trial 2, and 26.0% in the 3 trial; there was a significant difference (P<0.001) of the P4 formulation (trial 1: 47% DIV vs. 17% MAD-4; trial 2: 23% DIV vs. 5% MAD-4; trial 3: DIV 43% vs. MAD-4 8%). In the three trials there were differences in PC with ovarian status at the beginning: 19% for deep anestrus, 30% for shallow anestrous, and 46% for cycling (that represented a 3.8%). Primiparous presented better PC than the multiparous in trial 2 (28% vs. 18%). In trial 1 the body condition score at the beginning of the protocol affected PC (9% for ≤3, 21% for 3.5, 35% for 4 and 35% for ≥4.5; P<0.05). It was concluded that, in the conditions in which these trials were done, injectable progesterone would not be a good replacement for intravaginal device in a protocol for induction of ovulation with FTAI in postpartum anestrous beef in cows.