The number of oocytes recovered from Bos taurus indicus females subjected to ovum pick-up averaged two to four times greater compared to Bos taurus taurus females. The objective of the present study was to test the hypothesis that this difference in oocyte yield was due to more preantral follicles in the ovaries of Bos indicus females. Ovaries (n = 64) from Nelore (Bos indicus) fetuses (n = 10), heifers (n = 12), and cows (n = 10), and Aberdeen Angus (Bos taurus) fetuses (n = 10), heifers (n = 12), and cows (n = 10) were cut longitudinally into halves, fixed, and processed for histological evaluation. The number of preantral follicles was estimated by counting them in each histological section, using the oocyte nucleus as a marker and employing a correction factor. The average number of preantral follicles in the ovaries of Bos indicus vs Bos taurus was (mean ± SD) 143,929 ± 64,028 vs 285,155 ± 325,195 for fetuses, 76,851 ± 78,605 vs 109,673 ± 86,078 for heifers, and 39,438 ± 31,017 vs 89,577 ± 86,315 for cows (P > 0.05). The number of preantral follicles varied greatly among individual animals within the same category, as well as between breeds. In conclusion, we inferred that the higher oocyte yield from Bos indicus females was not due to a greater ovarian reserve of preantral follicles. Therefore, mechanisms controlling follicle development after the preantral stage likely accounted for differences between Bos indicus and Bos taurus females in number of oocytes retrieved at ovum pick-up.

Interest in indicus-taurus cattle has been increasing, as these animals are likely to present the best characteristics of Zebu and European bovine breeds. The aim of this study was to compare the embryo production of indicus-taurus donors with high vs low antral follicle counts obtained by ovum pickup/in vitro production (OPU/IVP) and superovulation (SOV)/embryo collection. Braford females at weaning age (3/8 Nelore × 5/8 Hereford, n = 137, 9 ± 1 month old) were subjected to six serial ovarian ultrasonographs and were assigned to two groups according to the number of antral follicles ≥ 3 mm as follows: G-High antral follicular count (AFC, n = 20, mean ≥ 40 follicles) and G-Low AFC (n = 20, mean ≤ 10 follicles). When the females (n = 40) reached 24 months of age, they were subjected to both OPU/IVP and SOV/embryo collection. The average number of follicles remained highly stable throughout all of the ultrasound evaluations (range 0.90-0.92). The mean number of COCs recovered (36.90 ± 13.68 vs 5.80 ± 3.40) was higher (p < 0.05) for females with high AFC, resulting in higher (p < 0.05) numbers of total embryos among females with high vs low AFC (6.10 ± 4.51 vs 0.55 ± 0.83). The mean number of embryos per collection was also higher (p < 0.05) for G-High vs G-Low (6.95 ± 5.34 vs 1.9 ± 2.13). We conclude that a single ultrasound performed at pre-pubertal ages to count antral follicles can be used as a predictor of embryo production following IVP and SOV/embryo collection in indicus-taurus females.

The objective was to compare populations of antral and pre-antral ovarian follicles in Bos indicus and Bos indicus-taurus cows with high and low antral follicle counts. Nelore (Bos indicus, n = 20) and Nelore X Angus (1/2 Bos indicus-taurus, n = 20) cows were subjected to follicular aspiration without regard to the stage of their oestrous cycle (day of aspiration = D0) to remove all follicles ≥3 mm and induce growth of a new follicular wave. Ovaries were examined by ultrasonography on D4, D19, D34, D49 and D64, and antral follicles ≥3 mm were counted. Thereafter, cows were assigned to one of two groups: high or low antral follicular count (AFC, ≥30 and ≤15 antral follicles, respectively). After D64, ovaries were collected after slaughter and processed for histological evaluation. There was high repeatability in the numbers of antral follicles for all groups (range 0.77-0.96). The mean (±SD) numbers of antral follicles were 35 ± 9 (Bos indicus) and 38 ± 6 (Bos indicus-taurus) for the high AFC group and 10 ± 3 (Bos indicus) and 12 ± 2 (Bos indicus-taurus) follicles for the low AFC. The mean number of preantral follicles in the ovaries of Bos indicus-taurus cows with high AFC (116 226 ± 83 156 follicles) was greater (p < 0.05) than that of Bos indicus cows (63 032 ± 58 705 follicles) with high AFC. However, there was no significant correlation between numbers of antral and preantral follicles.

The aim of the present study was to compare the lipid profile in oocytes of indicus and 1/2 indicus × taurus cows with high and low antral follicle count (AFC)/oocyte yields. After an OPU procedure (D0), antral follicles ≥3 mm were counted by ultrasonography (D4, 19, 34, 49, 64), and cows were assigned to groups with either high AFC (≥30 follicles; indicus, NH group; 1/2 indicus × taurus, AH group) or low AFC (≤15 antral follicles; indicus, NL group; 1/2 indicus × taurus, AL group). The lipid profiles of the oocytes were determined by MALDI-MS. For GI, GII and GIII oocytes, the indicus samples tend to cluster separately from the 1/2 indicus × taurus samples. The lipid species [PC (P-38:5) + H](+) and/or [PC (P-36:2) + Na](+) , [PC (38:2) + H](+) , [PC (38:5) + Na](+) and [TAG (60:8) + NH(4) ](+) were more abundant in indicus (NH and NL groups) than 1/2 indicus × taurus. The higher lipid content in the indicus oocytes likely reflects differences in the rate of lipid metabolism and may contribute to oocyte competence and embryo development.

Bos taurus indicus females provide a greater in vivo oocyte recovery (2-4 times more) in comparision with Bos taurus taurus. This aspect has strongly contributed for the success of the embryo industry in Brazil. Little information is available to explain this difference. Our objective was to test the hypothesis that the difference in oocyte yield is a result of higher numbers of preantral follicles in the ovaries of B. indicus females. Ovaries (n = 44) of fetuses aging from 180 to 240 days and of heifers from 20 and 24 months were collected from Bos taurus indicus (Nelore) and Bos taurus taurus (Aberdeen Angus) females at a slaughterhouse. Fetal age was estimated from the crown-rump length (Evans HE and Sack WO 1973 Anat. Hist. Embryol. 2, 11-45). Ovaries from Nelore fetuses (n = 10) and heifers (n = 12) and Aberdeen Angus fetuses (n = 10) and heifers (n = 12) were cut longitudinally into two halves, fixed in Bouin’s solution, and processed for histological evaluation. The ovarian halves were dehydrated in alcohol, cleared with xylene, embbebed in paraffin, and serially sectioned at 7 μm. Every 120th section was mounted and stained with periodic acid Schiff and hematoxylin. The number of preantral follicles was estimated through the counting of follicles in each section using the nucleus of the oocyte as a marker and a correction factor (Gougeon A and Chainy GBN 1987 J. Reprod. Fertil. 81, 433-442). Only 1 ovary per female was analyzed. Preantral follicles were classified according to the developmental stage as primordial (1 layer of flattened granulosa cells surrounding the oocyte), primary (1 layer of cuboidal granulosa cells), or secondary (2 or more layers of cuboidal granulosa cells), and as normal or degenerated according to their morphological appearance. The number of preantral follicles was not normally distributed and was compared using the Mann-Whitney test. There was no difference (P > 0.05) between the average number of preantral follicles in the ovaries of Bos indicus and Bos taurus females. The average number of preantral follicles per female was 143 929 ± 253 (mean ± SD) and 285 155 ± 570 for Bos taurus and Bos indicus fetuses, respectively, and 76 851 ± 280 and 109 673 ± 293 for Bos taurus and Bos indicus heifers (P > 0.05), respectively. A large variation in numbers of preantral follicles was observed among individuals within the same category and between breeds. Our results suggest that there might be differences in mechanisms controlling follicle development after the preantral stage accounting for the greater oocyte yield from Bos indicus females. This work was supported by grants from the Universidad Nacional del Litoral (CAI+D program), Universidad Nacional de Lomas de Zamora, the Argentine National Agency for the Promotion of Science and Technology (ANPCyT), and the Argentine National Council for Science and Technology (CONICET).