174 Pregnancy rate and pregnancy loss in precocious primiparous Nelore cows treated with injectable progesterone pre- or post-timed artificial insemination

We aimed to evaluate the pregnancy per AI (P/AI) of precocious primiparous cows exposed to injectable progesterone (iP4) 7 days before the beginning of timed AI (TAI) protocol (Day 0), and compare the pregnancy loss (PL) of primiparous cows with active corpus luteum (CL) at 22 days post-TAI treated with iP4 pre- (Day −7) and/or post-TAI (Day 33) protocol. Primiparous Nelore cows aged 23 to 30 months with an average of 33 ± 0.3 days postpartum (DPP) at Day 0 were used. On Day −7, cows were randomly distributed into two groups: control (n = 465), no treatment; and iP4, treated with 150 mg of iP4 on Day −7 (n = 458). Cows were submitted to an E₂/P₄-based TAI protocol. A resynchronization protocol was started 14 days post-TAI (Day 25). On Day 33, colour Doppler ultrasound (PD1) was used to determine CL blood perfusion (CLBP) and detect nonpregnant cows (CLBP < 30%). Cows in control and iP4 groups with active CL (blood perfusion ≥ 30%) had the CLBP recorded and were randomly assigned to receive or not receive 150 mg of iP4 at Day 33, resulting in four experimental groups: control (n = 122), iP4-Pre (n = 124), P4i-Post (n = 124), and iP4-Pre/Post (n = 129). Cows with active CL on Day 33 were submitted to pregnancy diagnoses at 29–34 (PD2), 56–62 (PD3), and 94–146 (PD4) days post-TAI. Pregnancy loss was divided into potential PL (PD1 to PD2), early PL (PD2 to PD3), late PL (PD3 to PD4), and total PL (PD1 to PD4). Statistical analysis was performed in SAS using PROC GLIMMIX, considering the main effects of DPP (early (≤28 days) or late (>28 days)), CLBP (low (≤40%) or high (>40%)), BCS, and iP4 treatment Pre- and Post-TAI and their interactions. The P/AI at PD1 did not differ (P > 0.1) between control and iP4 groups (53% (247/465) vs 55% (253/458)). The P/AI was greater (P ≤ 0.05) in cows with late DPP (58% (328/566)) than in cows with early DPP (49% (172/355)). The iP4 treatment Pre- or Post-TAI or an interaction between the two factors did not affect (P > 0.1) the potential PL (9.6% (48/499)), early PL (4.87% (22/451)), late PL (3.5% (15/429)), and total PL (17% (85/499)). However, the total PL tended to be greater (P = 0.06) in cows with early DPP (22% (37/172)) than those with late DPP (15% (48/325)). Also, potential PL, late PL, and total PL were greater (P ≤ 0.05) in cows with low CLBP (17% (27/159), 7% (9/126), 26% (42/159), respectively) than with high CLBP on Day 33 (7% (21/321), 2% (6/285), 13% (42/321), respectively). In conclusion, iP4 treatments pre- and/or post-TAI did not affect the pregnancy rates or pregnancy losses in precocious primiparous Nelore cows; however, pregnancy losses are increased in cows with low CLBP at Day 22 after post-TAI and at early DPP.

Research was supported by Agropecuária Nelore Paranã and Ouforino Saúde Animal.