The present study aimed to assess whether conception rates in primiparous Nellore cows
suffer from the physiological condition of the ovary on day zero (D0) of the treatment of
fixed-time artificial insemination (IATF), and from the reuse of intravaginal progesterone
devices previously used in cycling cows. 776 primiparous Nellore cows with an average
postpartum period of 45 days were used. After ultrasound evaluation, the experimental
animals were divided according to the ovarian condition. In experiment 1, three experimental
groups were formed: Group 1 (G1) - cow cycling (CC), with the presence of corpus luteum;
Group 2 (G2) - non-cycling cows (NCC), with the presence of large follicles (≥ 6 mm); and
Group 3 (G3) - NCC, with the presence of small follicles (<6mm). In experiment 2, the
devices previously used in CC were randomly assigned to two experimental groups: Group A
(GA) - NCC, with the presence of large follicles (≥ 6 mm); and Group B (GB) - NCC, with
the presence of small follicles (<6 mm). The results revealed a conception rate in G1 (52.2%)
and G2 (50.2%), significantly higher when compared to G3 (35.0%). In GA, the conception
rate (60.0%) was significantly higher (P <0.05) when the devices previously used in CC were
reused for synchronization of estrus, when compared with devices previously used in NCC
(44.0%) ). On the other hand, in GB there was no effect of previous use of the devices on the
conception rate. In conclusion, the presence of corpus luteum and large follicles in the ovaries
at the D0 of the treatment of IATF and the reuse of intravaginal progesterone devices
recovered from cycling cows increases the conception rate in primiparous Nellore cows.
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