Lack of complete regression of the corpus luteum (CL) after prostaglandin F_2α (PGF) treatment can reduce fertility during timed AI (TAI) protocols. The main objective of this study was to evaluate the effect of a second treatment with PGF during the Ovsynch protocol on fertility to the timed AI (TAI). A total of 2,148 lactating dairy cows were used on 11 dairy farms in 4 different regions of the USA, 3 in WI, 3 in CA, 2 in NY, one in PA, one in NM, and one in TX. Cows were synchronized with Ovsynch (GnRH [Gonadorelin acetate; 100 µg/mL; GONAbreed, Parnell]-7d-PGF[Cloprostenol sodium; 250 µg/mL; estroPLAN; Parnell]-56h-GnRH-16h-TAI) for TAI at 50 ± 3 DIM. The cows were randomized to receive: (1) No additional treatments with PGF = Ovsynch, or (2) A second PGF treatment at 24 h after the first PGF treatment = PROCEPT. Statistical analyses were performed using PROC Logistic in SAS, with treatment and parity as factors. In the overall logistic regression model there was no significant effect of Farm (P = 0.712); although, treatment effects on individual farms ranged from positive (P = 0.01) to a tendency for a negative effect (P = 0.12). There was also no interaction of parity and treatment in the overall model (P = 0.741). Overall, there was a tendency (P = 0.068) for an effect of treatment on P/AI with an increase from 33.3% in Ovsynch compared with 36.1% in PROCEPT (2.8% absolute increase; 8.5% relative increase [2.8/33.3]). There was no effect of treatment in primiparous cows (37.1% [99/267] vs. 38.2% [99/259]; Ovsynch vs. PROCEPT; P = 0.393). However, there was a tendency for an effect of treatment in multiparous cows (32.0% [259/809] vs. 35.4% [288/813]; 10.7% relative increase; P = 0.073). When multiparous cows were evaluated by parity, it was found that there was an effect of treatment in cows of second and third lactation (P = 0.047) but no effect of treatment in older cows (P = 0.517). Thus, treatment with a second PGF during the Ovsynch protocol tends to increase pregnancies per TAI producing about 10% more pregnancies per TAI in multiparous cows, with a significant increase in second and third lactation cows.