Use of injectable progesterone at the beginning of the TAI protocol is not necessary in super-early resynchronization started 14 days after artificial insemination in Bos indicus beef heifers.

In a protocol for the resynchronization of ovulation starting 14 days (D14) after timed artificial insemination, the effects of short-action injectable progesterone (P4i) administration and the length of treatment with an intravaginal progesterone (P4) device on follicular dynamics, the conception rate (P/AI) and the percentage of false positives were evaluated in 1065 Nelore heifers previously timed-inseminated. On D14, P4 devices were inserted, and heifers allocated, based on a 2 × 2 factorial design, to receive (P4i) or not 50 mg of P4i (NoP4i), and to remove the P4 device after 6 (6Day) or 8 days (8Day). At the time of P4 device removal (D20 and D22), non-pregnancy diagnosis was performed using vascularization of the corpus luteum (VCL) evaluated. At this time, non-pregnant heifers received 150 µg of D-cloprostenol, 0.6 mg of estradiol cypionate and 300IU of eCG. TAI was performed 48 h after P4 device removal. For these heifers, ultrasound examinations were performed at P4 device removal and at TAI to evaluate follicular dynamics and at 30 days after TAI to evaluate the P/AI. Pregnant heifers based on VCL were evaluated using B-mode ultrasonography 10 days after Doppler ultrasound to evaluate the percentage of false positives. Statistical analyses were performed using the GLIMMIX procedure of SAS. There were no interaction effects between P4i and duration of treatment with a P4 device. The P/AI was diagnosed by Doppler, 1st TAI, 2nd TAI, total and percentage of false positives did not differ between heifers receiving or not P4i. Similarly, duration of treatment with a P4 device did not influence the P/AI by Doppler, 1st TAI, 2nd TAI and total. However, the percentage of false positives diagnoses was higher in 6Day heifers (P = 0.01). The diameter of largest follicle at P4 device removal was greater in the 8Day heifers (P = 0.001), and at TAI was higher in the P4i-treated heifers (P = 0.03). Additionally, the percentage of false positives diagnoses was lower in heifers that ovulated to the 1st TAI protocol (P = 0.001). In conclusion, for resynchronization 14 days after TAI, it is not necessary to inject P4i at the beginning of the protocol. In addition, P4 device removal after 6 instead of 8 days increases the percentage of false positives because of the earlier diagnosis (20 days after TAI), but does not interfere in P/AI of resynchronization protocol. Furthermore, the percentage of false positives is higher in heifers that did not ovulate to 1st TAI protocol.

Exposure to progesterone previous to the protocol of ovulation synchronization increases the follicular diameter and the fertility of suckled Bos indicus cows.

The objective was to evaluate the effect of injectable progesterone previous to the timed artificial insemination (TAI) protocol on follicular growth, ovulation and pregnancy rate of suckled Bos indicus cows. In experiment 1, 10 days before the beginning to TAI protocol (D-10), 431 suckled-anestrus Nelore cows (249 multiparous and 182 primiparous), were allocated to one of three treatments groups (control, P4i and P4iGnRH). At this moment, cows in the P4i and P4iGnRH group received 150 mg of injectable progesterone intramuscularly (Sincrogest injetável®, Ouro Fino, Brazil). On Day 0 (D0), all cows were synchronized using an estradiol/progesterone-based TAI protocol. Simultaneously, in the P4iGnRH group, cows received 10 µg of Busereline intramuscularly (Sincroforte®, Ouro Fino, Brazil). Ultrasound exams were performed to evaluate the diameter of the largest follicle (D0, D8 and D10), ovulation rate and diameter of the corpus luteum (D24). In experiment 2, 681 suckled Nelore cows (356 multiparous and 325 primiparous) were synchronized using an estradiol/progesterone-based TAI protocol and received treatments similar to experiment 1. TAI was performed 48 h after removal of the progesterone (P4) device. Pregnancy diagnosis was 30 d after TAI. In experiment 3, blood samples were collected to evaluated the progesterone concentration for 168 h after administration of injectable progesterone intramuscularly. Statistical analyses were performed by GLIMMIX procedure of SAS. In experiment 1, the diameter of the largest follicle (LF) on D10 (P = 0.21), follicular growth rate (P = 0.34) and ovulation rate (P = 0.62) were similar among experimental groups. However, there was difference among groups for the LF on D0 [Control (10.9 ±â€¯0.2 mm)b, P4i (12.7 ±â€¯0.3 mm)a and P4iGnRH (12.6 ±â€¯0.3 mm)a; P = 0.001], LF on D8 [Control (9.7 ±â€¯0.2 mm)b, P4i (10.4 ±â€¯0.2 mm)a and P4iGnRH (9.9 ±â€¯0.2 mm)ab; P = 0.05], presence of the CL on D8 [Control 0% (0/136)b, P4i 0% (0/140)band P4iGnRH 26.4% (38/144)a; P = 0.001], diameter of the CL on D24 [Control (19.7 ±â€¯0.4 mm)ab, P4i (20.1 ±â€¯0.4 mm)a and P4iGnRH (18.5 ±â€¯0.4 mm)b; P = 0.001] and pregnancy rate [Control 35.0% (78/223)b, P4i 45.9% (105/229)a and P4iGnRH 40.6% (93/229)ab; P = 0.01]. The circulating concentration of P4 remained above 1.5 ng/mL until 168 h after the P4i treatment. In conclusion, the injectable progesterone previous to the TAI protocol increased diameter of the LF on D0 and D8 without interfering on the ovulation rate. Furthermore, such exposure increases the pregnancy rate in suckled Nelore cows.

Molecular and endocrine factors involved in future dominant follicle dynamics during the induction of luteolysis in Bos indicus cows.

The growth profiles of the future dominant follicle (DF) and subordinate follicle (SF) and the gene expression of the granulosa cells during luteolysis induction in Bos indicus cows were evaluated. Forty cows were synchronized with a progesterone and estradiol based protocol. After synchronization, cows with a corpus luteum (CL) were evaluated by ultrasonography every 12 h, beginning at eight days post ovulation. Cows identified with a follicle of at least 6.0 mm in diameter in the second wave were split into two groups (BD-before follicular deviation and AD-after follicular deviation. In the BD group cows received 500 µg of cloprostenol (a synthetic analogue of prostaglandin F2α) when the DF reached a mean diameter of 7.0 mm (6.5-7.5 mm). In the AD group, cows received 500 µg of cloprostenol when the DF reached a mean diameter of 8.0 mm (7.5-8.5 mm). Cows in both groups were submitted to aspiration of the DF at 96 and 72 h after prostaglandin was given. Follicular aspirations were performed to quantify IGF1R, LHR and PAPPA transcripts in the granulosa cells. The diameter of the DF at the moment of prostaglandin administration (P = 0.001) and the growth rate of the SF (P = 0.05) were greater in the AD group. There was greater abundance of LHR transcripts in BD cows (P = 0.04). The remaining variables tested were similar between the experimental groups (P > 0.05). In conclusion, the induction of luteolysis before follicular deviation does not interfere with dominant follicle dynamics. However, it causes granulosa cell LHR down regulation.