Follicular dynamics, luteal characteristics, and progesterone concentrations in synchronized lactating Holstein cows with high and low antral follicle counts.

We performed two experiments in high milk-producing Holstein cows. First, we evaluated the repeatability of the antral follicle count (AFC) - where all follicles were ≥2 mm in diameter - during the days of the ovulation synchronization protocol for timed artificial insemination (TAI) in dairy cows (n = 20). In the second study we investigated the follicular dynamics and Doppler ultrasonography in cows with low (≤15 follicles, n = 9) and high (≥25 follicles, n = 9) AFC, and measured progesterone (P4) concentrations during CL evaluation. In addition, the diameter of the preovulatory follicle, area of blood flow of the preovulatory follicle, CL area, and CL blood flow were compared between groups with high and low AFC. Ultrasound examinations were performed during the days of the protocol and 10 days after ovulation to assess the CL. The constancy of the AFC was analyzed by calculating the repeatability. Parametric variables were analyzed using the t-test, and nonparametric variables were analyzed using the Mann-Whitney test (P ≤ 0.05). The repeatability of the AFC on different days of the protocol was 0.98. Cows with low AFC showed a greater diameter of the preovulatory follicle (16 ± 0.3 vs. 15 ± 0.4 mm), blood flow area of the preovulatory follicle (17.3 ± 2.3 vs. 8.1 ± 3.2 mm2), CL area (579.1 ± 16.9 vs. 405.8 ± 21.2 mm2), area of CL perfusion (97.1 ± 9.4 vs. 68.3 ± 5.2 mm2), as well as higher P4 levels (3.1 ± 0.2 vs. 2.2 ± 0.2 ng/mL). In high milk-producing Holstein cows, the AFC has high repeatability on different days of the TAI protocol, and cows with a low AFC show larger preovulatory follicles and CLs with greater perfusion, in addition to greater P4 concentrations in comparison to those cows with a high AFC.

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 bovine in vitro embryo production by ovarian follicular wave synchronization prior to ovum pick-up.

This study evaluated the effects of the synchronization of ovarian follicular wave emergence on the efficiency of in vitro embryo production. Bos indicus cows (n = 20) were divided into two groups (control vs. synchronization) and subjected to repeated ovum pick-up (OPU) sessions (8 replicates each, with an interval of 21 days in a 2 × 2 crossover design) and subsequent in vitro embryo production. Cows in the control group (n = 10) were submitted to OPU procedures without any stimulation every 21 days. Animals in the synchronization group received a protocol-based progesterone implant, estradiol benzoate and prostaglandin on a random day of the estrus cycle (Day 0) and the OPU was performed on Day 5. After in vitro production, embryos were transferred to recipients synchronized at a fixed time and the diagnosis was performed 60 days later. An evaluation of the parameters for each OPU session revealed that donors that received the synchronization protocol pre-OPU showed a greater number of embryos (5.9 ± 0.5 vs. 4.5 ± 0.4; P = 0.037), higher rate of embryo production (45.8% vs. 38.5%; P = 0.001) and higher mean number of conceptions per group (2.2 ± 0.2 vs. 1.6 ± 0.2; P = 0.07) in relation to the group that did not receive hormonal treatment. We concluded that synchronization of the follicular wave prior to OPU showed positive effects on in vitro embryo production as well as on pregnancy rates.

The development and integrity of equine pre-antral follicles cultured in vitro with follicle-stimulating hormone (FSH) supplementation.

This study investigated the effects of different concentrations of FSH (10, 50, 100 and 200 ng/ml) in supplemented MEM+ on the development of equine pre-antral follicles that were cultured in vitro for 2 or 6 days. The ovaries (n = 5) from mares in seasonal anoestrus were collected from a local abattoir. Ten ovarian tissue fragments of approximately 3 × 3 × 1 mm were obtained from each animal. The fragments were cultured in situ for 2 days (D2) or 6 days (D6) in MEM+ or MEM+ supplemented with FSH at four different concentrations, establishing the following 11 groups: control (D0); MEM + (D2); MEM + (D6); MEM + 10 ng/ml of FSH (D2); MEM + 10 ng/ml of FSH (D6); MEM + 50 ng/ml of FSH (D2); MEM + 50 ng/ml of FSH (D6); MEM + 100 ng/ml of FSH (D2); MEM + 100 ng/ml of FSH (D6); MEM + 200 ng/ml of FSH (D2); and MEM + 200 ng/ml of FSH (D6). Follicles were observed in only 9.65% (388 of 4,018) of the histological sections. Of the 861 follicles evaluated, 488 were in the primordial stage, and 373 were in various developmental stages; 59.7% were morphologically normal. Regarding the integrity of the pre-antral follicles, the groups with 100 ng/ml FSH of 2-days culture as well as 50, 100 and 200 ng/ml FSH of 6-days culture provided the best results. In conclusion, the in vitro culture of abattoir-derived equine ovarian fragments presented better morphological integrity when supplemented with FSH for 6 days, in comparison with the MEM culture group. However, no clear effects were observed with FSH regarding the promotion of activation from a primordial to a developing follicle.

Regional distribution and integrity of equine ovarian pre-antral follicles.

The goal of this study was to determine the distribution of pre-antral follicles in the ovarian parenchyma of mares. For Experiment 1, each ovary was cut longitudinally at the greater curvature, performing two hemiovaries. After that, six fragments from each hemiovary were obtained, resulting in 12 fragments, which were divided into the innermost region of the parenchyma, the middle region and the outermost region. All the three obtained sections were cut transversally to obtain two fragments from each one. For Experiment 2, each ovary also submitted to a longitudinal cut on the greater curvature, forming two hemiovaries. Each hemiovary was sectioned into four symmetrical fragments, resulting in eight fragments per ovary. The fragments were related as being near to or far from the ovulatory fossa. The fragments of both experiments were immediately fixed in Carnoy for 12 hr and kept in 70% ethanol for 24 hr. Follicles were classified according to the stages of development and for morphological integrity according to oocyte morphology and granulosa cells. After the histological assessment, a total of 1,130 follicles were visualized from Experiment 1, being 1,054 (93.3%) primordial follicles and 76 (4.7%) follicles in development. The innermost region had the highest percentage of pre-antral follicles compared to the other regions (p < .05). The middle and outermost regions showed higher percentages of intact primordial and developing follicles than the innermost region (p < .05). Considering Experiment 2, 938 follicles were found, being 894 (95.3%) primordial and 44 (4.7%) follicles in development. The region near the ovulatory fossa presented higher (58.7%; 551 of 938) follicular concentration compared to the region far from the ovulatory fossa (41.3%; 387 of 938; p < .05). As a conclusion, distribution of pre-antral follicles in the equine ovary has a specific pattern through the parenchyma. Also, the follicular integrity differed in the studied ovarian areas.

Correlation between phenotype, genotype and antral follicle population in beef heifers.

The present study was performed in indicus-taurus heifers 1) to determine if the antral follicle count (AFC) exhibits repeatability from puberty to yearling age and 2) to evaluate whether the phenotypic and genotypic parameters used in genetic improvement programs are correlated with AFC. In study I, Braford heifers (3/8 Nelore x 5/8 Hereford, n = 137) were serially examined by ultrasonography (with 60-day intervals) from weaning (9 ± 1 mo of age) to yearling ages (20 ± 1 mo of age) to monitor the numbers of antral follicles. In study II, the AFC of animals from experiment I and contemporary (same farm, considered at same age and kept under same conditions heifers n = 270 18-24 months) was correlated with the records of a genetic selection program using four statistical models with different covariates: i) model 1 considered effects of contemporary group and covariates age, weight gain from birth to weaning and visual scores for carcass traits at weaning, ii) model 2 covered contemporary group, age, weight gain from weaning to yearling and visual scores for carcass traits at yearling. The effects, variables and covariates of models 1 and 2 were combined to form model 3. Model 4 included the model 3 with addition of paternal effect. In study I, AFC varied from 3 to 64 follicles among females but was highly repeatable (0.89-0.92) within individuals in the same group. In study II, the four models tested showed low correlations with AFC: 0.072, 0.056, 0.082 and 0.172 for models 1, 2, 3 and 4, respectively. However, the model with paternal effect provided 17% of correlation of AFC and genotypic and phenotypic characteristics. Models 1, 3 and 4 also showed that AFC in indicus-taurus heifers can be influenced by finishing precocity at weaning (P < 0.05) with a variation of three follicles. Based on these studies, AFC in heifers from weaning to yearling age is highly variable between individuals and repeatable within the same female. Additionally, there is no correlation between phenotypic or genotypic characteristics and the antral follicle population. However, AFC can be slightly affected by finishing precocity at weaning.

Use of sexed sorted semen for fixed-time artificial insemination or fixed-time embryo transfer of in vitro-produced embryos in cattle.

Artificial insemination and in vitro embryo production are powerful tools for disseminating superior genetic qualities and improving the reproductive performance of dairy and beef cattle. In conjunction with these biotechnologies, sexed-sorted semen has been used to obtain offspring of a predetermined sex. This study compared the pregnancy rates obtained using in vitro fertilization/timed embryo transfer (IVF/TET) and timed artificial insemination (TAI), both performed using sexed-sorted (Y-chromosome-bearing) semen obtained from the same bull. For the in vitro embryo production, the ovaries of 250 Nelore cows with known histories were collected in the slaughterhouse and used for IVF. After evaluation of the recipients (IVF/TET group; n = 974), the resultant embryos were transferred to the females with corpus luteum (n = 822). The pregnancy-related data for this group were compared with those for the TAI group (n = 974). Ultrasonography was performed at 60 days to determine the pregnancy status and confirm the sex of the fetus. A total of 2008 oocytes produced 1050 embryos, with 52% of them reaching the blastocyst stage. The pregnancy rate and the accuracy in determining the fetal sex were 35.4% (345/974) and 95.07% (328/345), respectively, for the IVF/TET group and 30% (293/974; P < 0.05) and 94.88% (278/293), respectively, for the TAI group. In the present study, we concluded that male calves could be better obtained using IVF/TET rather than TAI; therefore, this strategy can be considered to increase the pregnancy rate of beef cattle.

Pregnancy rate and birth rate of calves from a large-scale IVF program using reverse-sorted semen in Bos indicus, Bos indicus-taurus, and Bos taurus cattle.

Obtaining sexed sperm from previously frozen doses (reverse-sorted semen [RSS]) provides an important advantage because of the possibility of using the semen of bulls with desired genetic attributes that have died or have become infertile but from whom frozen semen is available. We report the efficiency of RSS on the pregnancy rate and birth rate of calves in a large-scale program using ovum pick-up and in vitro embryo production (IVEP) from Bos indicus, Bos indicus-taurus, and Bos taurus cattle. From 645 ovum pick-up procedures (Holstein, Gir, and Nelore), 9438 viable oocytes were recovered. A dose of frozen semen (Holstein, Nelore, Brahman, Gir, and Braford) was thawed, and the sperm were sex-sorted and cooled for use in IVF. Additionally, IVF with sperm from three Holstein bulls with freeze-thawed, sex-sorted (RSS) or sex-sorted, freeze-thawed (control) was tested. A total of 2729 embryos were produced, exhibiting a mean blastocyst rate of 29%. Heifers and cows selected for adequate body condition, estrus, and health received 2404 embryos, and 60 days later, a 41% average pregnancy rate was observed. A total of 966 calves were born, and 910 were of a predetermined sex, with an average of 94% accuracy in determining the sex. Despite the lower blastocyst rate with freeze-thawed, sex-sorted semen compared with sex-sorted semen, (P < 0.05), the pregnancy rate (bull I, 45% vs. 40%; II, 35% vs. 50%; and III, 47% vs. 48% for RSS and control, respectively; P > 0.05) and sex-sorted efficiency (bull I, 93% vs. 98%; II, 96% vs. 94%; and III, 96% vs. 97% for RSS and control, respectively; P > 0.05) were similar for each of the three bulls regardless of the sperm type used in the IVF. The sexing of previously frozen semen, associated with IVEP, produces viable embryos with a pregnancy rate of up to 40%, and calves of the desired sex are born even if the paternal bull has acquired some infertility, died, or is located a long distance from the sexing laboratory. Furthermore, these data show the feasibility of the process even when used in a large-scale IVEP program.

Dynamics of follicular growth and progesterone concentrations in cyclic and anestrous suckling Nelore cows (Bos indicus) treated with progesterone, equine chorionic gonadotropin, or temporary calf removal.

The objective of this study was to investigate the effects of eCG and temporary calf removal (TCR) associated with progesterone (P4) treatment on the dynamics of follicular growth, CL size, and P4 concentrations in cyclic (n = 36) and anestrous (n = 30) Nelore cows. Cyclic (C) and anestrous (A) cows were divided into three groups. The control group received 2 mg of estradiol benzoate via intramuscular (IM) injection and an intravaginal device containing 1.9 g of P4 on Day 0. On Day 8, the device was removed, and the animals received 12.5 mg of dinoprost tromethamine IM. After 24 hours, the animals received 1 mg of estradiol benzoate IM. In the eCG group, cows received the same treatment described for the control group but also received 400 UI of eCG at the time of device removal. In the TCR group, calves were separated from the cows for 56 hours after device removal. Ultrasound exams were performed every 24 hours after device removal until the time of ovulation and 12 days after ovulation to measure the size of the CL. On the same day as the CL measurement, blood was collected to determine the plasma P4 level. Statistical analyses were performed with a significance level of P ≤ 0.05. In cyclic cows, the presence of the CL at the beginning of protocol resulted in a smaller follicle diameter at the time of device removal (7.4 ± 0.3 mm in cows with CL vs. 8.9 ± 0.4 mm in cows without CL; P = 0.03). All cows ovulated within 72 hours after device removal. Anestrous cows treated with eCG or TCR showed follicle diameter at fixed-timed artificial insemination (A-eCG 10.2 ± 0.3 and A-TCR 10.3 ± 0.5 mm) and follicular growth rate (A-eCG 1.5 ± 0.2 and A-TCR 1.3 ± 0.1 mm/day) similar to cyclic cows (C-eCG 11.0 ± 0.6 and C-TCR 12.0 ± 0.5 mm) and (C-eCG 1.4 ± 0.2 and C-TCR 1.6 ± 0.2 mm/day, respectively; P ≤ 0.05). Despite the similarities in CL size, the average P4 concentration was higher in the A-TCR (9.6 ± 1.4 ng/mL) than in the A-control (4.0 ± 1.0 ng/mL) and C-TCR (4.4 ± 1.0 ng/mL) groups (P < 0.05). From these results, we conclude that eCG treatment and TCR improved the fertility of anestrous cows by providing follicular growth rates and size of dominant follicles similar to cyclic cows. Additionally, TCR increases the plasma concentrations of P4 in anestrous cows.

Antral follicle populations and embryo production--in vitro and in vivo--of Bos indicus-taurus donors from weaning to yearling ages.

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.

Comparison of antral and preantral ovarian follicle populations between Bos indicus and Bos indicus-taurus cows with high or low antral follicles counts.

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.

Resynchronization of estrous cycle with eCG and temporary calf removal in lactating Bos indicus cows.

The aim of this study was to compare four methods of estrus resynchronization performed 23 days after timed artificial insemination (TAI) plus estrus observation in Bos indicus cows. Eight hundred fourteen lactating Nelore cows were submitted to TAI and then randomly assigned to one of the five following treatments: R23 (resynchronization without eCG), R23/200 (resynchronization with 200 IU of eCG), R23/300 (resynchronization with 300 IU of eCG), R23/TCR (resynchronization with temporary calf removal [TCR]), and a control group, with estrus observation followed by AI (with no resynchronization). Treatment consisted of a progesterone device plus administration of estradiol benzoate on Day 0; on Day 8, the device was removed and cloprostenol was applied, together with estradiol cypionate. Also on Day 8, either eCG was administered or TCR was performed in the resynchronized groups, except for R23. The females were inseminated 48 hours after device removal or TCR (33 days after the first TAI). The control group was kept under estrus observation from 18 to 23 days after the first TAI and was inseminated 12 hours after detection of estrus. The first pregnancy evaluation was performed using ultrasound examination 31 days after the first TAI. After 30 days of the resynchronization, a second pregnancy evaluation was performed and the animals in the R23/300 and R23/TCR groups achieved the highest conception rates, 76.6% and 74.0%, respectively (P < 0.05). There were no differences between the conception rates of the animals in the R23/200 (63.3%), R23 (61.3%), and control (54.3%) groups (P > 0.05). These results suggest that estrus resynchronization at 23 days after TAI can effectively improve the conception rate of lactating Bos indicus cows in a short time period. Furthermore, resynchronization with 300 IU of eCG or with TCR provided the best results.