Antral follicle count, oocyte production and embryonic developmental competence of senescent Nellore (Bos indicus) cows

Information on the follicular population and oocyte quality of cows in the final period of reproductive life is scarce. The present study aimed to compare the antral follicle count (AFC), oocyte production and embryonic developmental competence of young versus long-lived and senescent Bos indicus beef cows. Nellore cows (Bos indicus) were classified into three groups according to age: young (4-9 years, n = 10), long-lived (14-17 years, n = 10) and senescent (17-23 years, n = 10). At a random time in the estrus cycle, the cows received cloprostenol sodium salt (0.5 mg, IM), estradiol benzoate (1 mg, IM) and an intravaginal P4 device (1.4 g). Five days later, the P4 devise was removed and oocyte collection (OPU1) was performed. A second OPU (OPU2) was performed 5 days after the first in order to aspirate only growing follicles. During each OPU, AFC and the number and quality of cumulus-oocyte complexes (COCs) were evaluated. Then, the COCs were placed in standard maturation medium (IVM), fertilized and incubated for 9 days. The data were subjected to ANOVA and Multinomial Logistic Regression. The AFC was smaller in long-lived and senescent cows in both OPU1 and OPU2 when compared to younger cows. There was no difference in AFC between OPU1 (19.9 +/- 1.8) and OPU2 (17.6 +/- 1.9) in young cows, however, more follicles were punctured in long-lived and senescent cows in OPU1 (12.0 +/- 2.6 and 19.3 +/- 4.6) than in OPU2 (9.2 +/- 1.9 and 10.3 +/- 2.3), respectively (P < 0.01). The numbers of COCs recovered from young cows (OPU1 = 14.2 +/- 1.8; OPU2 = 8.4 +/- 0.9) were higher than those obtained from long-lived cows (OPU1 = 5.9 +/- 2.3; OPU2 = 4.3 +/- 1.0) and senescent cows (OPU1 = 7.2 +/- 3.0; OPU2 = 4.1 +/- 1.7), respectively (P < 0.05). The cleavage rate did not differ between groups. However, the rate of blastocyst formation was higher for young (64.8%) and long-lived (65.0%) compared to senescent (16.5%) cows (P 0.01). In conclusion our results indicate that the AFC is lower in long-lived and senescent cows compared with young cows. However, unlike in senescent cows, the embryonic development of long-lived cows is similar to that of young cows. This suggests that Nellore cows aged 17 years begin to have reduced embryonic development capacity due to ovarian aging. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

The research compared antral follicle count, oocyte production, and embryonic development competence of young, long-lived, and senescent Bos indicus cows. The study found that long-lived and senescent cows had lower AFC compared to young cows, but young cows had higher oocyte production. In terms of embryonic development, young and long-lived cows had higher blastocyst formation rates.