Effect of estradiol cypionate and GnRH treatment on plasma estradiol-17β concentrations, synchronization of ovulation and on pregnancy rates in suckled beef cows treated with FTAI-based protocols

Estradiol cypionate administered at the end of a progesterone-based protocol for FTAI induces ovulation and improves postovulatory luteal function and uterine environment in anestrous beef cows

The objective of this study was to evaluate the effect of the administration of estradiol cypionate (ECP) at the end of an estradiol and progesterone-based protocol for fixed time artificial insemination (FTAI) on ovarian response and uterine function in postpartum anestrous beef cows. Multiparous suckled cows were randomly assigned to receive ECP at doses of 0 (control, n = 15), 0.5 (n = 15) or 1.0 mg (n = 15) im at the time of progesterone intravaginal insert removal. Serum 17β-estradiol concentrations at 24 h after insert removal were greater (P < 0.05) in both ECP treatments than in controls. No differences in estradiol were found between 0.5 mg and control cows (P > 0.1) from 48 h after insert removal until ovulation, although greater (P < 0.05) concentrations were maintained until ovulation in 1.0 mg ECP treated cows. Maximum 17β-estradiol concentration attained in each female was greater as ECP dose was greater (10.4 ± 0.4, 11.8 ± 0.5 and 13.5 ± 0.7, for control, 0.5 and 1.0 mg ECP treated cows, respectively; P < 005). Proportion of cows that ovulated tended to be greater (P = 0.06) in ECP treated than in control cows. Ovulation occurred earlier and the size of the ovulatory follicle was smaller (P < 0.05) for 1.0 mg but not for 0.5 mg (P > 0.1) when compared with control cows. After ovulation (Day 13 and 14), serum progesterone concentrations were greater (P < 0.05) in 0.5 and 1.0 mg ECP than control cows. Uterine environment on Day 6 after ovulation was affected by treatment; transcript expression of three of nine evaluated genes (i.e., estrogen, IGF-1 and insulin receptors genes) were upregulated (P < 0.05) after ECP treatment. In conclusion, ECP administration at progesterone insert removal in anestrous cows i) induces greater serum estradiol concentrations and tended to induce greater ovulation rate, ii) acts in a dose-dependent manner, as ECP dose increases ovulation occurs earlier and the size of the ovulatory follicle is smaller, iii) improves postovulatory luteal function and affects uterine gene expression. Altogether, this information contributes with the understanding of the effect of preovulatory estradiol exposure on ovulation and postovulatory ovarian and uterine function in anestrous beef cows.

Effects of extending the length of pro-oestrus in an oestradiol- and progesterone-based oestrus synchronisation program on ovarian function, uterine environment and pregnancy establishment in beef heifers

The aim of the present study was to investigate the effects of a strategy for extending pro-oestrus (the interval between luteolysis and ovulation) in an oestrus synchronisation protocol (named J-Synch) in beef heifers on follicular growth, sexual steroid concentrations, the oestrogen receptor ERα and progesterone receptors (PR) in the uterus, insulin-like growth factor (IGF) 1 and pregnancy rates. In Experiment 1, heifers treated with the new J-Synch protocol had a longer pro-oestrus period than those treated with the conventional protocol (mean (± s.e.m.) 93.7 ± 12.9 vs 65.0 ± 13.7 h respectively; P < 0.05). The rate of dominant follicle growth from the time of progesterone device removal to ovulation was greater in heifers in the J-Synch than conventional group (P < 0.05). Luteal area and serum progesterone concentrations were greater in the J-Synch Group (P < 0.05) for the 12 days after ovulation. Progesterone receptor (PGR) staining on Day 6 after ovulation in the uterine stroma was lower in the J-Synch than conventional group (P < 0.05), and the expression of PR gene (PGR) and IGF1 gene tended to be lower in J-Synch-treated heifers (P < 0.1). In Experiment 2 (n = 2349), the pregnancy rate 30–35 days after fixed-time AI (FTAI) was greater for heifers in the J-Synch than conventional group (56.1% vs 50.7% respectively). In conclusion, our strategy for extending pro-oestrus (i.e. the J-Synch protocol) significantly improves pregnancy establishment in beef heifers. This improvement was related to an increased rate of growth of the dominant ovulatory follicle, greater progesterone concentrations during the ensuing luteal phase and different uterine patterns of PGR and IGF1, which may have favoured embryo development and pregnancy establishment.