Expression of estrus increases fertility and decreases pregnancy loss in timed-AI or timedET protocols

The objective was to evaluate if expression of estrus in dairy cattle altered fertility in timed AI (TAI) or timed ET (TET) protocols that used estradiol and progesterone (E2/P4) to synchronize ovulation. A retrospective analysis was performed of past studies in which lactating dairy cows received the following protocol: 2mg Estradiol Benzoate (d– 11 Estrogin/Farmavet/SP/Brazil) +intravaginal P4 device (1.9g CIDR®/Zoetis/SP/Brazil) 7d later 25mg of PGF (d-4 Lutalyse/Zoetis/SP/Brazil) 2d later CIDR removal+1mg of ECP (d-2 ECP/Zoetis/SP/Brazil). Two days after CIDR removal, cows received TAI (d0; n=5,430) or on d7 TET (n=2,003). Binomial variables were analyzed using PROC GLIMMIX. Ovarian ultrasonographies (US) were performed on d0 and d7 to determine ovulatory follicle diameter. Only cows with a visible CL on d7 were used in this study. At the time of CIDR removal, all cows received tailchalk and cows with complete removal of tail chalk by d0 were considered to have expressed estrus. Circulating P4 concentrations were evaluated on d7. Pregnancies per AI (P/AI) or ET (P/ET) were determined by US on d32 and d60. At d32 pregnancy diagnosis (PD), cows with expression of estrus had increased (P 17 mm) of follicles had lower P/AI. There was no effect of ovulatory follicle diameter on P/ET in cows that expressed estrus (P=0.34); although, cows that did not express estrus had lower P/ET if they ovulated larger follicles (P=0.05). In cows that showed estrus, follicle diameter did not affect pregnancy loss after TAI (P=0.43) or TET (P=0.34), but in cows that showed no estrus, cows that ovulated larger follicles had greater pregnancy loss after TAI (P=0.04) or TET (P=0.04). Expression of estrus during protocols for TAI or TET is associated with an increase in fertility. In TAI programs, optimizing follicle diameter, increasing circulating P4 on d7 after AI and expression of estrus were associated with increased fertility. However in cows with TET, the association of fertility with either ovulatory follicle diameter or P4 on d7 was less dramatic and seemed to be related to whether cows expressed estrus.