Influence of sperm post-thaw subpopulations of angus and nelore bulls on pregnancy rates by fixed-time artificial insemination

BACKGROUND

The heterogeneity of ejaculate indicates that fertility is still variable among bulls and that more stringent evaluation methods are needed to identify the ejaculates suitable for AI.

OBJECTIVE

To identify and characterize the sperm subpopulations (SP) in thawed semen doses of Nelore and Angus bulls and to evaluate the influence of these sperm subpopulations on pregnancy rate in cows submitted to fixed-time AI (FTAI).

MATERIALS AND METHODS

A dose of post-thawed semen from each bull (n=18; consisting of Angus n = 9 and Nelore n = 9) was analyzed for: sperm kinetics; morphology and plasma membrane integrity; and the determination of the sperm subpopulations. Differences between the groups were estimated with the t-test considering a significance level of <5%.

RESULTS

There was no influence between breeding bulls for sperm morphology, plasma membrane integrity, and pregnancy rate (P > 0.05). Regarding the kinetic parameters evaluated by the CASA system, Nelore had greater values, for cells with slow velocity (Angus: 16.4 %; Nelore: 21.7%; P = 0.028). In contrast, ANGUS bulls had more static cells (Angus: 27.2%; Nelore: 9.3%; P = 0.048). Based on CASA system data and clustering procedures, four sperm subpopulations were statistically established. In Angus bulls, a higher level of fast and nonlinear spermatozoa were found in SP3 (33.3%), followed by SP1 (32.7%%) with fast and progressive spermatozoa. Whereas, SP1 of Nelore bulls had 33.8% fast and progressive spermatozoa, followed by 32.2% of SP3 with fast and nonlinear spermatozoa.

CONCLUSION

Both breeds of bulls presented similar proportions of sperm SP. Consequently, no influence on the pregnancy rates was shown in cows submitted to the IATF programs on a large scale. doi.org/10.54680/fr22310110312.

Antral follicle population in prepubertal and pubertal heifers

The antral follicle count (AFC) is an important tool in the selection of bovine females destined for biotechnology. However, little is known about AFC in prepubertal and pubertal heifers. Some challenges inherent to the physiology of young females must be considered to achieve efficient rates with different procedures, such as ovum pick-up and IVF. This paper covers some important topics about ovarian physiology related to the population of antral follicles and reproductive efficiency in young female cattle.

Improvement of development of equine preantral follicles after 6 days of in vitro culture with ascorbic acid supplementation

The aim of this study was to evaluate the effects of different concentrations of ascorbic acid (25, 50, and 100 μg/mL) in supplemented minimum essential medium (MEM+) on the development of equine preantral follicles that were cultured in vitro for 2 or 6 days. The contralateral ovaries (n = 5) from five mares in seasonal anestrus were collected from a local abattoir. Nine ovarian tissue fragments of approximately 5 × 5 × 1 mm were obtained from each animal. One fragment was immediately fixed and subjected to histologic analysis (control group; Day 0), and the other eight were placed in PBS supplemented with penicillin (200 IU/mL) and streptomycin (200 mg/mL) at 4 °C for 1 hour (during transport to the laboratory). The fragments were cultured in situ for 2 days (D2) or 6 days (D6) in MEM+ or MEM+ plus ascorbic acid at three different concentrations, establishing the following nine groups: control; MEM+ (D2); MEM+ (D6); MEM+ 25 μg/mL of ascorbic acid (D2); MEM+ 25 μg/mL of ascorbic acid (D6); MEM+ 50 μg/mL of ascorbic acid (D2); MEM+ 50 μg/mL of ascorbic acid (D6); MEM+ 100 μg/mL of ascorbic acid (D2); and MEM+ 100 μg/mL of ascorbic acid (D6). The preantral follicles were classified according to their stage (primordial, primary, secondary, or antral) and their morphology (normal or abnormal). Slides (n = 951) including 4450 histologic sections were evaluated. Follicles were observed in only 4.85% (216 of 4450) of the histologic sections. Of the 407 follicles evaluated, 120 were in the primordial stage and 287 were in different developmental stages; additionally, 43.5% were morphologically normal. After 6 days of culture, the groups cultured with 50 and 100 μg/mL of ascorbic acid differed in terms of follicular development compared with the other groups. On the basis of occurrence of follicular development and the presence of viable follicles, it can be concluded that a positive effect of culture for 6 days in MEM+ supplemented with 50 and 100 μg/mL of ascorbic acid was observed on equine ovarian fragments.

233 HIGH NUMBERS OF ANTRAL FOLLICLES INFLUENCE THE IN VITRO EMBRYO PRODUCTION, BUT NOT THE CONCEPTION RATE OF FIXED-TIME ARTIFICIAL INSEMINATION IN NELORE CATTLE

The aim of this study was to compare the conception rates to fixed-time artificial insemination (FTAI) and in vitro embryo production between Nelore cows with high or low antral follicle counts (AFC). First, multiparous Nelore cows (Bos indicus, n = 547, 40–60 days postpartum) were subjected to synchronization of ovulation. Randomly during their oestrous cycle (Day 0), cows received an intravaginal device containing 1.9 g of P4 (CIDR®) and 2 mg of oestradiol benzoate (Estrogin®), intramuscularly. At device removal (Day 8), cows received 500 µg of PGF2α (Ciosin®), 300 IU of eCG (Novormon®), and 1 mg of oestradiol cipionate (ECP®), intramusculary. All cows were inseminated 48 h after P4 device removal. Antral follicles = 3 mm were counted using an intravaginal microconvex transducer (Day 0), and cows were assigned to groups of high (G-High, = 25 follicles, n = 183), intermediate (G-Intermediate, 16–20 follicles, n = 183), or low AFC (G-Low, = 10 follicles, n = 181). In another study to compared the in vitro embryo production, Nelore cows (n = 66, 72–96 months) were subjected to ultrasound-guided follicular aspiration using an intravaginal microconvex array transducer (7.5 MHz). The COC were selected and cows were assigned to groups according to the oocyte production: G-High (n = 22, = 40 oocytes), G-Intermediate (n = 25, 18–25 oocytes), or G-Low (n = 19, = 7 oocytes). Previously tested semen from a single bull was used for IVF using a previously described protocol (Silva-Santos et al. 2014 Reprod. Domest. Anim. 49, 228–232). The oocyte and embryo production (viable embryo: grade I, II, III; vitrifiable embryo: grade I, II) were evaluated. The number of follicles was evaluated by Kruskal-Wallis, and the chi-square test was used for data on oocyte and embryo production (P = 0.05). The average follicular population was 30.7 ± 5.7 (G-High), 18.6 ± 1.64 (G-Intermediate), and 7.8 ± 2.4 follicles (G-Low; P < 0.05), but there were no differences in the conception rates among groups (51.9 v. 48.6 v. 58.6%, respectively; P > 0.05). The total number of oocytes recovered were 1109 (G-High), 534 (G-Intermediate), and 101 (G-Low; P < 0.05). The mean number of viable oocytes was 40.4 ± 10.6 (G-High), 14.8 ± 3.0 (G-Intermediate), and 3.8 ± 1.1 (G-Low; P < 0.05) and the percentage of viable oocytes was 80% (G-High), 69% (371/534, G-Intermediate), and 71% (G-Low; P < 0.05). Cleavage rate was 79% (G-High), 74% (348/472, G-Intermediate), and 71% (G-Low; P < 0.05), and blastocyst rate was 42% (G-High), 32% (153/472, G-Intermediate), and 13% (G-Low; P < 0.05). The number of viable embryos was 18.4 ± 6.7 (G-High), 6.1 ± 3.6 (G-Intermediate), and 0.6 ± 0.7 (G-Low; P < 0.05) and the percentage of vitrifiable embryos was 81% (G-High), 77% (118/153, G-Intermediate), and 58% (G-Low; P < 0.05). Therefore, Nelore cows with high oocyte production had ~10-fold higher oocyte production and produced ~30-fold more embryos compared with the low AFC group. In conclusion, AFC had no influence on the conception rates to FTAI; however, Nelore cows with high oocyte production exhibited higher in vitro embryo production.