Is estradiol valerate an alternative to estradiol benzoate in promoting the synchronization of ovulation and timed artificial insemination in suckled Bos indicus beef cows?

The objective of the present study was to evaluate the effect of estradiol valerate administered at the beginning of the ovulation synchronization protocol on the pregnancy rate of Bos indicus cows. In the experiments, the following products from MSD, Sao Paulo, Brazil were used: estradiol valerate (EV), estradiol benzoate (EB), intravaginal progesterone device (P4), estradiol cypionate (EC), equine chorionic gonadotropin (eCG) and cloprostenol (PGF). In Experiment 1, Bos indicus cows (n=899) with a body condition score (BCS) of 2.76 ± 0.01 were included in a 3 (device) × 2 (protocol: 5 mg of EV or 2 mg of EB) factorial design. There were three types of P4 devices: a new device (New), a device previously used for 9 days (1×), and a device previously used for 18 days (2×). Nine days later (D9), the P4 device was removed, and cows received 300 IU of eCG. In addition, cows in the EB group received 1 mg of EC and 265 µg of PGF. Timed artificial insemination (TAI) was performed 48 h after P4 device removal in the EB group (TAI48) and 54 h after P4 device removal in the EV group (TAI54). In Experiment 2, Bos indicus cows (n=434) with a BCS of 2.62 ± 0.01 received a new P4 device or one previously used for 9 days and 5 mg of EV. On D9, all cows received 300 IU of eCG, and the P4 devices were removed and distributed in TAI48 and TAI54 cows. In Experiment 3, Bos indicus cows (n=429) with a BCS of 2.80 ± 0.01 were divided into the control and EV/EC groups. All cows received a P4 device. In addition, cows in the control group received 2 mg of EB, and cows in the EV/EC group received 5 mg of EV on D0. On D9, all cows received 1 mg of EC and 300 IU of eCG, and the P4 devices were removed. Cows in the control group also received 265 µg of PGF. All cows were inseminated 48 h after the removal of the P4 device. In Experiment 1, there was no effect of the interaction between protocol and P4 device on the occurrence of estrus (P=0.45) or on the pregnancy per artificial insemination ratio (P/AI; P=0.30). In addition, the occurrence of estrus and P/AI were not different between in the two estradiol groups (P=0.12 and P=0.82) and across the types of intravaginal P4 device (P=0.91 and P=0.47). In Experiment 2, the pregnancy rate was lower (tendency) in TAI48 cows (P=0.07). In Experiment 3, the estrus rate (P=0.12) and P/AI (P=0.56) were similar between the experimental groups. In summary, protocols using estradiol valerate without exogenous ovulation induction require adjustments in the timing of AI from 48 to 54 h after P4 device removal. However, a combination of estradiol valerate at the beginning of the protocol and estradiol cypionate nine days later successfully induced ovulation in Bos indicus cows inseminated 48 h after P4 device removal.

Use of injectable progesterone to replace the intravaginal progesterone device on the ovulation synchronization protocol reduces the pregnancy rate in Bos indicus cows.

The aim of this study was to evaluate the effectiveness of using different doses of injectable progesterone (P4i) in a new ovulation synchronization protocol in place of progesterone (P4)-releasing intravaginal devices in Bos indicus cows. For this, three experiments were carried out. To determine the P4-release curve (Experiment 1), 55 Bos indicus cows were distributed into 5 experimental groups for the administration of different doses of P4i at D0 (P4i60, n = 11; P4i105, n = 11; P4i150, n = 11; P4i195, n = 11 and P4i240, n = 11) and submitted to the ovulation synchronization protocol (D0: P4i + EB; D8: PGF2α + EC + eCG). Daily blood samples were collected by jugular venipuncture from D0 to D12 for analysis of the serum P4 profile. To evaluate ovarian follicular dynamics and the timing of ovulation (Experiment 2), three studies were conducted with different doses of P4i at the beginning of the ovulation synchronization protocol (Study a: 150 mg and 105 mg P4i; Study b: 75 mg P4i; Study c: 60 mg P4i). At the end of the ovulation synchronization protocol, after ovulation inducing administration, ultrasound examinations were performed every 24 h until 96 h or until ovulation was detected (Studies a, b and c). To evaluate the pregnancy rate (Experiment 3), 132 Bos indicus cows were subjected to an ovulation synchronization protocol using either a 75 mg progesterone injection (Group P4i75) or an intravaginal P4 device (control group) on D0. Pregnancy was determined by ultrasound 30 days after the end of the ovulation synchronization protocol. All statistical analyses were performed by SAS®. In the P4-release curve, the peak occurred on D1 and on D3 all concentrations remained below 1 ng/mL until the end of the study (D12) in all groups. The ovulation rates were similar between the 75 mg dose group and the Control group (P = 0.24 - Experiment 2 - study b), result not observed with other doses of P4i (study a and c). The pregnancy rate (Experiment 3) was greater [P4i Group 27% and Control Group 72.7% (P = 0.0001)] in cows receiving the intravaginal P4 device. In conclusion, the use of long-acting P4i (75 mg) to replace the intravaginal P4 device negatively affects the conception rate of Bos indicus cows submitted to ovulation synchronization protocol.