Early resynchronization of follicular wave emergence among Nelore cattle using injectable and intravaginal progesterone for three timed artificial inseminations

ABSTRACT Follicular dynamics and pregnancy per AI (P/AI) of cattle submitted to resynchronization 13 d after TAI using a progesterone (P4) insert and supplementary injectable progesterone (iP4) were determined. There was synchronization of ovulation timing imposed (Day0 = expected estrus; Experiment 1). On Day13, animals were assigned to: control (only P4 insert; 15 cows and 13 heifers) and iP4 (P4 insert+100 mg iP4; 13 cows and 12 heifers) groups, and submitted to daily ovarian ultrasonography and blood collection (Day13 to Day22). In Experiment 2, 760 suckled cows and 498 heifers were submitted to a TAI on Day-0 and assigned into control and iP4 groups on Day13. In animals with luteolysis on Day22, there was a second TAI on Day24, and on Day37 were subjected to the opposite treatments as imposed in first resynchronization procedure. On Day37, there was pregnancy diagnosis in animals with functional CL. The third TAI was performed on Day48. Day of follicular wave emergence did not differ between groups and parities. Dominant follicles were larger in cows than heifers, and in animals of the control group on Day24. Greater P4 concentrations were detected on Day14 and Day15 in the iP4-treated animals. Luteolysis occurred earlier in cows than heifers. Overall P/AI percentage as a result of second and third TAIs, regardless of parity, was greater in iP4-treated animals. In conclusion, females treated with a supplementary iP4 had a greater plasma P4 concentration and P/AI, but there was no effect of iP4 treatment on synchrony of timing of follicular wave.