Conception rate and pregnancy loss in fixed-time cattle embryo transfer programs are related to the luteal blood perfusion but not to the corpus luteum size.

This study aimed to evaluate the effect of luteal blood perfusion and corpus luteum (CL) area on the conception rate and occurrence of pregnancy loss of recipients in a large-scale fixed-time embryo transfer (FTET) program. Multiparous Brangus cows (n = 1700) at 45 days postpartum and body condition scores (BCS) between 2.5 and 4.0 (3.0 ± 0.3) were used in this study. On a random day of the estrous cycle (day -10), the females received progesterone and estradiol based on the FTET protocol. On day 7, 1465 recipients had at least one CL and were evaluated using B-mode ultrasound for the CL area (cm2) and color Doppler for the luteal blood perfusion score (I/low-vascularization area <40% of the CL; II/medium-vascularization >45% to < 50%; and III/high-vascularization >50%). Immediately after CL evaluation, each recipient received a single fresh embryo (blastocyst stage) ipsilateral to the CL, in vitro produced from a commercial laboratory. Pregnancy diagnosis was performed at 30 days and repeated 60 days later to evaluate pregnancy loss (30-90 days). Ultrasound evaluation and embryo transfer were performed by a single technician. For data analysis, in addition to luteal blood perfusion groups, recipients were retrospectively ranked according to CL area into small (<3 cm2; 2.63 ± 0.01), medium (>3 to < 4 cm2; 3.44 ± 0.01), and large (>4 cm2; 4.77 ± 0.03). Data were analyzed using a logistic regression model (P < 0.05). The overall conception rate was 44.2% (648/1465), influenced by the luteal blood perfusion score [P = 0.03; high 48.4%a (134/277), medium 44.6%a (427/958), and low 37.8%b (87/230)] but not by CL area ranking [P = 0.37; large 41.8% (225/538), medium 45.2% (276/610), and small 46.4% (147/317)]. There was no interaction between the luteal blood perfusion score and CL area ranking (P = 0.81), and the BCS did not affect the results of this study (P = 0.51). In terms of pregnancy loss up to 90 days, there was no effect on the CL area ranking (P = 0.77), but the flow score showed an effect [P = 0.03; high 3.6%b (5/139), medium 9.3%a (44/471), and low 10.3%a (10/97)]. The conception rate and occurrence of pregnancy loss in the FTET program in beef cattle are related to luteal blood perfusion but not CL size.

Ovarian follicular dynamics and conception rate in Bos indicus cows with different antral follicle counts subjected to timed artificial insemination.

Two experiments in Nelore cows subjected to timed artificial insemination (TAI) were designed to compare the influence of the antral follicle count (AFC/AFCs) on (1) ovarian follicular dynamics and (2) conception rates. First, multiparous cows with high (≥45 follicles; n=43) or low (≤15 follicles; n=32) AFCs were selected to undergo a TAI protocol to monitor ovarian follicular dynamics. Second, the AFCs of 962 cows also subjected to TAI were determined and classified as groups of high (G-high; ≥45 follicles; n=194), intermediate (G-intermediate; ≥20≤40 follicles, n=397) or low (G-low; ≤15 follicles; n=243) AFCs. In study I, the ovarian measurements (diameter, perimeter and area) were greater (P≤0.05) and there was a greater consistency in number of antral follicles during the period of synchronization for TAI in the high than low group. Effects of the AFC and ultrasonic evaluation interval on the follicular diameter were observed (P≤0.05); however, there was no interaction (P>0.05). Dominant follicles had greater diameters (P≤0.05) in the G-low than in the G-high at D4 (7.3±2.2 vs. 6.2±1.4mm, respectively, P=0.06), D8 (11.2±1.8 vs. 9.5±1.8mm, respectively), D9 (12.3±1.7 vs. 10.6±1.7mm, respectively), and D10 (13.4±1.3 vs. 12.2±1.8mm, respectively), as well as greater estimated diameters of ovulatory follicles (14.4±1.5 vs. 13.4±2.1mm, respectively, P=0.08). In study II, the cows with fewer AFCs had greater (P≤0.05) conception rates (61.7%) than the cows with the intermediate (52.9%) and greater (49.5%) AFCs. Nelore cows with fewer AFCs subjected to synchronization of time of ovulation had a larger follicular diameter and a greater conception rate than the groups with intermediate and a greater AFCs.

High numbers of antral follicles are positively associated with in vitro embryo production but not the conception rate for FTAI in Nelore cattle.

The objective was to compare the conception rates for FTAI and in vitro embryo production between Nelore cows with different antral follicle counts (AFC=number of follicles ≤3mm in diameter in the ovaries). Nelore cows (n=547) were subjected to ovulation synchronization. Randomly during the estrous cycle (D0), cows received an intravaginal device containing 1.9g P4 (CIDR(®)) and 2mg BE (Estrogin(®)), IM. When the device was removed (D8), the cows received 500µg PGF2α (Ciosin(®)), 300IU eCG (Novormon(®)) and 1mg EC (ECP(®)), IM. All cows were inseminated 48h after P4 device removal. Antral follicles ≥3mm were counted using an intravaginal microconvex transducer (D0), and the cows were assigned to high (G-High, ≥25 follicles, n=183), intermediate (G-Intermediate, 16-20 follicles, n=183) or low AFC groups (G-Low, ≤10 follicles, n=181). In another experiment, COCs were retrieved by OPU from Nelore cows (n=66), which were assigned to groups according to oocyte production: G-High (n=22, ≥40 oocytes), G-Intermediate (n=25, 18-25 oocytes) or G-Low (n=19, ≤7 oocytes). All COCs from the same cow were cultured individually (maximum of 25 COCs per drop) and then in vitro fertilized using thawed frozen sperm (2×10(8)/dose) from a Nelore sire of known fertility. The data were analyzed using a Kruskal-Wallis and a Chi-square test (P≤0.05). There was no difference in the conception rates after FTAI between Nelore cows with high, intermediate or low AFC (51.9 vs. 48.6 vs. 58.6%). 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). Therefore, AFC had no influence on the conception rates for FTAI; however, Nelore cows with high oocyte production exhibited better in vitro embryo production.

The correlation between the number of antral follicles and ovarian reserves (preantral follicles) in purebred Bos indicus and Bos taurus cows.

The objectives of this study were to compare populations of preantral follicles between purebred Bos indicus and Bos taurus cows with high or low antral follicle counts (AFC) and to correlate the number of preantral follicles with the population of antral follicles. Nelore (Bos indicus, n=100) and Angus (Bos taurus, n=100) cow ovaries were collected at abattoirs and examined using ultrasonography. Antral follicles ≥3mm were counted, and the cows ovaries were assigned to high (G-High) or low (G-Low) AFC groups based on the mean number (±1 SD) of ovarian antral follicles: Bos indicus with high AFC (≥57 follicles, n=8) or low AFC (≤21 follicles, n=8) and Bos taurus with high (≥45 follicles, n=10) or low AFC (≤13 follicles, n=10). The ovaries were processed, and the number of preantral follicles was estimated. Between-groups comparisons were performed using a Kruskal-Wallis test, and the correlation between preantral and antral follicles was evaluated using a Pearson's correlation test (P≤0.05). A large variation in the number of preantral follicles was observed among the animals. Although there was a correlation between the population of preantral follicles and the number of antral follicles, there was no difference between the mean number of preantral follicles in the Bos indicus G-High (48,349±30,149) and G-Low groups (33,037±31,710) or between the Bos taurus G-High (35,050±36,060) and G-Low groups (30,481±43,360). Therefore, the preantral follicle population did not differ between purebred Bos indicus and Bos taurus cattle with high or low AFC but was correlated with the number of antral follicles. In addition to the large within-groups variation in the number of preantral follicles, some cows with high AFC had lower populations of preantral follicles compared to the low AFC group, and the highest population of preantral follicles was observed in both Bos indicus and Bos taurus with low AFC.