An investigation of vascularity of ovarian and uterine arteries after hormonal treatment for inactive ovaries using the short-term progesterone-based programme had not yet been explored in repeat-breeder crossbred dairy cows. To investigate the in vivo follicular and uterine arterial indices as an indicator of successful hormonal stimulation for inactive ovaries in repeat-breeder crossbred dairy cattle, 59 cows with inactive ovaries were induced with a 5-day progesterone-based protocol. At the completion of hormonal synchronisation, cows were divided into two groups according to the size of the largest follicle (LF) on their ovary: small (≤10.0 mm) and large (>10.0 mm) LFs. Vascularities of LF and uterine artery (UtA) were evaluated using a colour Doppler tool. Cows that presented with large LF had greater follicular and UtA vascular indices (p < 0.001) and pregnancy rate (p < 0.01) than cows bearing small LF on their ovary. There was a positive correlation (p < 0.001) between follicular size and LF and UtA vascular indices. Our findings highlighted that in vivo LF and UtA vascular indices at the completion of hormonal stimulation might be a promising indicator for predicting success in ovarian response to hormonal stimulation for inactive ovaries of infertile crossbred dairy cows.

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The antral follicle count (AFC) is a test in which the number of oocyte-containing follicles that are developing in both ovaries are visually counted. The count of these follicles strongly relates to the population of the growing follicle reserve on the ovaries. However, the importance of the main number of antral follicle populations (mAFC) in mono-ovulatory animal species has yet to be completely elucidated. Moreover, the investigation of the ovarian interrelationship with unilateral mAFC (main number of antral follicle populations appearing on only one side of the ovary) and bilateral mAFC (main number of antral follicle populations appearing in equivalent numbers on both sides of the ovary) and how understanding this interrelationship can offer possible indicators of ovarian response to hormonal induction have not yet been investigated in mono-ovulatory Bos indicus beef cows. The aim of this study is to investigate the different ovarian interrelationships of mAFC (unilateral and bilateral mAFC) at the time of exogenous hormonal stimulation on the total number of AFC (left and right ovaries) at the beginning of the hormonal protocol for ovarian stimulation and ovarian response at the completion of exogenous hormonal stimulation as well as their usefulness as possible biomarkers of successful hormonal stimulation in Bos indicus beef cattle. Beef cows (n = 104) with low total numbers of AFC (4.7 ± 2.4 follicles) were stimulated with a gonadotropin-releasing hormone-progesterone-prostaglandin F2α-based protocol. At the beginning of the hormonal protocol, ovarian ultrasound scans were performed to evaluate AFC from both ovaries of cows. Beef cows were divided into two groups, unilateral (n = 74) and bilateral mAFC (n = 30), according to the ovarian interrelationship. At the completion of the hormonal stimulation, ovarian ultrasound scans were performed to evaluate the dominant follicle (DF) and cows with DF > 8.5 mm in diameter emerging on their ovaries were defined as having experienced a response to hormonal stimuli. There was a difference of 19.1% between Bos indicus cows bearing unilateral mAFC that produced an increase in ovarian response (odds ratio = 2.717, p < 0.05) compared to the responsive rate of cows displaying bilateral mAFC (82.4% vs. 63.3%). In unilateral mAFC, cows bearing mAFC ipsilateral to the ovary of dominant follicle (DF) had a higher responsive rate than cows bearing mAFC contralateral to the DF ovary (50.0% vs. 32.4%, p < 0.05). In mAFC ipsilateral to the DF ovary, pregnancy rates were greatest in cows bearing mAFC and DF on the right ovary compared with cows bearing mAFC and DF on the left ovary (25.0% vs. 9.1%, p < 0.05). In primiparous and multiparous cows, unilateral mAFC occurs with a greater (p < 0.05) frequency than bilateral mAFC (69.0% and 72.0% vs. 31.0% and 28.0%, respectively). In unilateral mAFC, primiparous cows bearing mAFC ipsilateral to the DF ovary had a greater responsive rate than primiparous cows bearing mAFC contralateral to the DF ovary (55.0% vs. 20.0%, p < 0.05). In mAFC ipsilateral to the DF ovary, responsive and pregnancy rates were greatest (p < 0.05) in multiparous cows bearing mAFC and DF on the right ovary compared with multiparous cows bearing mAFC and DF on the left ovary (58.1% and 22.6% vs. 25.8% and 3.2%, respectively). Furthermore, there was a positive correlation between the mean diameter of AFC at the time of the exogenous hormonal trigger and the mean diameter of DF at the completion of hormonal synchronisation (p < 0.05). Our findings emphasise that the ovarian interrelationship with unilateral mAFC at the time of the hormonal trigger might be a promising biomarker for predicting success in ovarian response to hormonal stimulation of mono-ovulatory Bos indicus beef cows with low AFCs.

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Background: Lower concentrations of endogenous progesterone (P) after fertilization, due to corpus luteum (CL) dysfunction, leads to an increased embryonic loss and reduced pregnancy outcomes not only in female cattle but also in women. Therefore, an increase in the number of corpora lutea (CLs) may improve fertility in infertile bovine females. The aim of the current study was to investigate the influence of increased number of CLs by creating accessory CL on plasma P concentration and fertility in bovine repeat-breeder females undergoing the short-term fixed-time artificial insemination (FTAI) protocol.Methods: In experiment 1, 32 female cattle had induced ovulation with the short-term (5-day) P-based protocol. To induce additional CL, cows were treated with gonadotropin releasing hormone (GnRH) on day 5 post-induction. On day 14, only female cattle with at least one CL on their ovaries were classified into two groups: 1CL (original CL; n = 14) and 2CLs groups (original CL + accessory CL; n = 8). In experiment 2, 213 bovine repeat-breeder females were bred using the short-term FTAI protocol. On day 5 post-FTAI, cows were divided into two groups: treatment with (GnRH5-treated group; n = 113) or without (GnRH5-untreated group; n = 100) GnRH. On day 14 post-FTAI, cows were sub-divided into two groups: 1CL (n = 115) and 2CLs (n = 39) groups.Results: In experiment 1, the ovarian luteal diameter, area, and volume per total CLs were greater in 2CLs group compared with 1CL group (P < 0.001). On days 12 and 14 post-induction, female cattle bearing two CLs had greater P concentrations than female cattle bearing only one CL on their ovaries (P < 0.05). In experiment 2, CL number and pregnancy rates were greater in GnRH5-treated group compared with GnRH5-untreated group (P < 0.01). Pregnancy rates were greater in 2CLs cows compared with 1CL cows (P < 0.01). Moreover, female cattle bearing two CLs had a greater likelihood of pregnancy (odds ratio = 20.86) than female cattle bearing only one CL on their ovaries (P = 0.001). Conclusions: In bovine model, our findings confirmed a beneficial effect of an additional CL on ovarian hormone and fertility in infertile female cattle. The results highlighted that increased number of CLs by creating additional CL leads to enhanced peripheral P concentrations and improved pregnancy outcomes in bovine repeat-breeder females undergoing the short-term FTAI protocol.