Ovarian dynamics in response to two modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocols designed for use in Brahman heifers

Understanding the Ovarian Interrelationship with Low Antral Follicle Counts (AFC) in the In Vivo Bos indicus Cow Model: Unilateral and Bilateral Main AFC as Possible Biomarkers of Ovarian Response to Hormonal Synchronisation

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.

Progesterone-based timed AI protocols for Bos indicus cattle I: Evaluation of ovarian function

Three experiments evaluated ovarian dynamics and circulating progesterone (P4) during P4-based protocols initiated with GnRH, estradiol benzoate (EB), or no additional treatment in Nelore (Bos indicus) cattle. In Exp 1 (n = 59 cows), a 5-d P4-only protocol (P-5d; D0: P4 implant alone (1g); D5: P4 removal, 0.5 mg estradiol cypionate [EC], 0.526 mg cloprostenol [PGF], and 300 IU equine chorionic gonadotropin [eCG]; D7: 8.4 μg buserelin acetate [GnRH]) was compared to a 9d protocol initiated with EB (EB-9d; D0: 2 mg EB + P4; D9: P4 removal + EC + PGF + eCG), and to a 7d GnRH protocol (G-7d; D0: 16.8 μg GnRH + P4; D6: PGF + eCG; D7: P4 removal + PGF; D9: GnRH). Exp 2 (n = 55 cows) compared G-7d and EB-7d protocols (similar to EB-9d, but D9 treatments were done on D7). Exp 3 (n = 64 heifers) compared EB-7d, G-7d, and P-5d protocols. For all experiments, daily ovarian ultrasonography was done from D0 until 4d after implant withdrawal and blood samples were collected at D0 and first PGF. Follicle dynamics were determined for each individual animal, analyzed within individual experiments, and afterwards combined to determine overall effects of treatments. The protocol that began with GnRH, G-7d, had greater ovulation rate after D0 with subsequently greater number of CL and circulating P4 at time of PGF (52.8%, 1.0 ± 0.1 CL, 4.0 ± 0.4 ng/mL) than for EB protocols (12.1%, 0.4 ± 0.05 CL, 2.0 ± 0.2 ng/mL), or P-5d (2.5%, 0.6 ± 0.09 CL, 2.6 ± 0.3 ng/mL). The G-7d and EB protocols had synchronized follicle wave emergence in 92.1% of animals but with distinct patterns. For the G-7d group, wave emergence occurred earlier in ovulating than non-ovulating animals (1.4 ± 0.2 d vs 2.5 ± 0.4 d). By comparison, most animals in EB-7d or EB-9d (80.3%) displayed atresia of the dominant follicle, followed by wave emergence 2-3 d after EB treatment. In contrast, P-5d protocol synchronized wave emergence in only 30.0% of cows. Nevertheless, no differences among treatments were detected for ovulation at end of the protocol (85.7%). In conclusion, the P-5d protocol did not synchronize follicle wave emergence but produced similar final ovulation, whereas, GnRH and EB protocols had follicle dynamics synchronized by distinct mechanisms that produced differences in CL number and P4 at the time of PGF treatment but similar final ovulation. Based on ovarian function, each of these synchronization methods are promising for use in FTAI, although fertility still needs to be evaluated.

Associations among thermal biology, preovulatory follicle diameter, follicular and luteal vascularities, and sex steroid hormone concentrations during preovulatory and postovulatory periods in tropical beef cows

The objectives were to evaluate effects of tropical seasons on thermal biology, preovulatory follicle (POF) diameter, POF and luteal vascularities, and estradiol (E2) and progesterone (P4) concentrations; and to determine the associations among the values for these variables during preovulatory and postovulatory periods in Thai native cows in tropical climates: cold, hot, and rainy seasons. Development and vascularity of the POF and corpora lutea (CL) were evaluated using color Doppler ultrasonography. The temperature-humidity index (THI) was greater when the preovulatory period occurred during the rainy season when compared with the occurrence during the hot and cold seasons of the year. Furthermore, POF diameter was less when the THI was greater. The THI was greater when the postovulatory period occurred during the rainy season when compared to the occurrence of the postovulatory period during the hot and cold seasons of the year. Furthermore, the CL vascularity and P4 concentration were less when the THI was greater. The THI was inversely correlated with CL vascularity and P4 concentrations. When the THI was greatest during the hot and rainy seasons of the year, there were the greatest negative effects on POF size, POF and CL blood flow, and concentrations of E2 and P4 during the preovulatory and postovulatory periods. While native Bos indicus are capable of adapting to tropical conditions, there are still negative effects, such as impaired POF and CL functions, when the THI induces heat stress.

Locational relationship between corpus luteum and ovulatory follicle on ovaries alters follicular dynamics and progesterone concentrations of Thai indigenous beef cows exhibiting two follicular waves

The present study aims to determine the impact of differences in the locational relationship between the previous corpus luteum (CL) and the further ovulatory follicle (OF) on follicular dynamics and progesterone (P4) concentrations in Thai indigenous beef cows (White Lamphun) exhibiting two follicular waves. Twenty-one cows, exhibiting the two-wave follicular pattern, were studied through interovulatory intervals (IOI), and classified according to the relationship between the previous CL and the further OF on the cattle model ovaries. Classifications were outlined as either an ipsilateral (same ovary) relationship (n = 12), or a contralateral (opposite ovaries) relationship (n = 9). Ultrasound monitoring, which evaluated the follicular diameter, and collection of blood for determining the P4 concentration were performed each day throughout the IOI. The IOI was longer (P &lt; 0.05) in the contralateral cows than in the ipsilateral cows (19.7 ± 0.33 days vs 18.5 ± 0.29 days). Cows with an ipsilateral relationship were found to have further OFs with greater (P &lt; 0.05) diameters than were cows with a contralateral relationship (13.9 ± 0.31 mm vs 12.1 ± 0.21 mm). The mean growth rate of the further OF was greater (P = 0.05) in the ipsilateral cows than in the contralateral cows (1.1 ± 0.11 mm/day vs 0.8 ± 0.04 mm/day). On Day 17 of the IOI, the ipsilateral cows demonstrated their lowest concentration of P4 (P &lt; 0.05). On Day 18 of the IOI, the concentrations of P4 tended to be lower (P = 0.09) in the ipsilateral cows than in the contralateral cows (0.6 ± 0.04 ng/mL vs 1.1 ± 0.12 ng/mL). The interval from the luteinisation until the end of the luteolysis was longer (P &lt; 0.05) in the contralateral group than in the ipsilateral group (18.5 ± 0.50 days vs 16.7 ± 0.33 days). Thus, we conclude that in Thai indigenous beef cows, the growth rate and diameter of the further OF during luteolysis increases more in the ipsilateral relationship than in the contralateral relationship.

Genome-wide association for the outcome of fixed-time artificial insemination of Brahman heifers in northern Australia

Fixed-time AI (FTAI) is a powerful tool for genetic improvement of extensively managed beef cattle. A genomewide association study (GWAS) was conducted to investigate genes and genetic markers associated with the outcome (pregnant or not pregnant) of FTAI in 614 commercial Brahman heifers genotyped for 18,895 SNP and imputed to 51,588 SNP. The likelihood of Brahman heifers becoming pregnant after hormonal treatment to synchronize ovulation followed by FTAI was influenced by the content of their genomes, as determined by a principal component analysis. The principal component analysis involved comparisons between the studied heifers and populations of known and ancestry. The heritability of FTAI outcome was = 0.18, which is higher than for most other reproductive outcome traits. The number of SNP associated with FTAI outcome was 101 ( < 0.001, false discovery rate = 0.53). Compared with all SNP tested, associated SNP had a tendency for highly divergent allelic frequencies between and . Associated SNP were located in nearly all chromosomes, a result that shows a complex genetic architecture that is typical of highly complex traits with low heritability. Considering this and previous GWAS that examined Brahman heifer puberty and postpartum anestrus interval, 3 genomic regions emerge as important for overall Brahman heifer fertility, which mapped to chromosomes 1, 7, and 9. Further analyses, including improved genome annotation, are required to elucidate the link between these regions and heifer fertility. Additional studies are needed to confirm SNP and gene associations reported herein and further elucidate the genetics of FTAI outcome. Future GWAS should target other Braham populations and additional cattle breeds with FTAI records, including breeds with higher ancestry.

A field investigation of a modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocol designed for fixed-time artificial insemination of Brahman heifers

Pregnancy rates (PR) to fixed-time AI (FTAI) in Brahman heifers were compared after treatment with a traditional oestradiol-based protocol (OPO-8) or a modified protocol (OPO-6) where the duration of intravaginal progesterone releasing device (IPRD) was reduced from 8 to 6 days, and the interval from IPRD removal to oestradiol benzoate (ODB) was increased from 24 to 36 h. Rising 2 yo heifers on Farm A: (n = 238 and n = 215; two consecutive days AI); B (n = 271); and C (n = 393) were allocated to OPO-8 or OPO-6. An IPRD was inserted and 1mg ODB i.m. on Day 0 for OPO-8 heifers and Day 2 for OPO-6 heifers. On Day 8, the IPRD was removed and 500 μg cloprostenol i.m. At 24h, for OPO-8 heifers, and 36 h, for OPO-6 heifers, post IPRD removal all heifers received 1mg ODB i.m. FTAI was conducted at 54 and 72 h post IPRD removal for OPO-8 and OPO-6 heifers. At Farm A, OPO-6 heifers, AI on the second day, the PR was 52.4% to FTAI (P = 0.024) compared to 36.8% for OPO-8 heifers. However, no differences were found between OPO-8 and OPO-6 protocols at Farm A (first day of AI) (39.9 vs. 35.7%), or Farms B (26.2 vs. 35.4%) and C (43.2% vs. 40.3%). Presence of a corpus luteum at IPRD insertion affected PR to FTAI (43.9% vs. 28.8%; P < 0.001). This study has shown that the modified ovulation synchronisation protocol OPO-6 may be a viable alternative to the OPO-8 protocol for FTAI in B. indicus heifers.

Influence of biostimulation and temporary weaning on follicular dynamics and pregnancy rates in Nelore cows (Bos taurus indicus)

The objective of this study was to evaluate the effect of biostimulation and temporary weaning on the follicular dynamics and pregnancy rates in Nelore cows. We used three groups of 75 cows: a control group without biostimulation and suckling calves (WB), a group that was biostimulated and had suckling calves (BE) and a group that was biostimulated and subjected to temporary weaning for 56 h (BETW). Ovarian dynamics were examined using ultrasonography. All groups showed follicular atresia. The interval between beginning of the treatment and wave emergence was 3.25 ± 0.30 days for BE, 3.40 ± 0.27 days for BETW and 3.37 ± 0.50 days for WB. The time between implant removal and ovulation was 64.50 ± 1.88 h for BE, 66.75 ± 1.35 h for BETW and 60.85 ± 3.10 h for WB. Eight cows were submitted to ultrasound analysis, and the percentages of cows that had ovulatory follicles of the new follicular wave with maximum diameters greater than 0.80 cm were 100 % (8/8) in BE (1.28 ± 0.12 cm), 100 % (8/8) in BETW (1.52 ± 0.07 cm) and 87.5 % (7/8) in WB (1.21 ± 0.10 cm). The pregnancy rate was 52 % (39/75) in BE, 69.3 % (52/75) in BETW and 37.3 % (28/75) in WB. The association of biostimulation and temporary weaning increased follicular development, ovulation synchronisation and, consequently, the pregnancy rate in beef cows.