Evaluation of prostaglandin and injectable progesterone in the early postpartum period on uterine health parameters, follicular dynamics, and fertility in beef cattle.

The postpartum period presents significant reproductive challenges and remains relatively understudied in beef cattle. This study evaluated the effects of prostaglandin F2α (PGF2α) and injectable progesterone (iP4) on uterine health, ovarian dynamics, and pregnancy per insemination in Nelore cows subjected to timed artificial insemination (TAI) during early postpartum. In Study I, cows at 10 days postpartum (dpp) were randomly assigned to one of four groups: Control (0.9 % NaCl, n = 10); PGF2α (0.5 mg cloprostenol, n = 10); iP4 (150 mg, n = 10); or PGF2α+iP4 (0.5 mg cloprostenol and 150 mg iP4, n = 10). Animals were evaluated for uterine inflammation-based on polymorphonuclear cell count (PMN) and uterine body diameter-at 10 and 30 dpp, and underwent an estradiol/progesterone-based TAI protocol to monitor follicular dynamics. In Study II, which was specifically designed to assess pregnancy outcomes, cows at 22 ± 2 dpp were randomized into the same four treatment groups: Control (n = 520), PGF2α (n = 513), iP4 (n = 521), and PGF2α+iP4 (n = 506). At 10 dpp, PMN counts were similar among treatment groups (p = 0.23) but showed a significant reduction by 30 dpp (p < 0.05). No treatment effect was observed at 30 dpp on PMN counts (p = 0.89) or incidence of subclinical endometritis (p = 0.53). Uterine diameter decreased (p < 0.05) in all groups from 10 to 30 dpp, except in the iP4 group. At 30 dpp, the PGF2α and iP4 groups showed a larger dominant follicle diameter compared to controls. PGF2α-treated cows ovulated earlier (p = 0.01), and those receiving PGF2α tended to respond better to the TAI protocol (p = 0.06). In Study II, the PGF2α+iP4 group achieved the highest pregnancy per TAI rate (354/506; 70 %), outperforming the PGF2α (333/513; 64.9 %), iP4 (331/521; 63.5 %), and Control (325/520; 62.5 %) groups (p = 0.05). Treatment with PGF2α+iP4 in early postpartum Nelore cows improved pregnancy rates following TAI.