The aim of this study was to evaluate the effect of age of Nellore (Bos indicus) donors on the efficiency of in vitro embryo production (IVEP) and pregnancy rate. Thirty‐six donors, including 11 female calves (13 ± 0.61 months), 17 prepubertal heifers (25 ± 0.78 months) and 8 cows (83 ± 28 months), were submitted to 3 procedures of ovum pickup (OPU) on random days of the estrous cycle at intervals of 21 days. Caspase‐3 and IGFBP2 were quantified in oocytes and blastocysts for the evaluation of oocyte and embryo quality. The produced embryos were vitrified (n = 445) and transferred to synchronized recipients. Cows produced a larger number of follicles (cows: 54.5 ± 6.2; calves: 20.0 ± 0.57; prepubertal heifers: 20.8 ± 0.46), total oocytes (cows: 45.97 ± 7.22; calves: 28.93 ± 6.14; prepubertal heifers: 27.21 ± 4.94) and cleaved oocytes (cows: 21.14 ± 4.22; calves: 13.09 ± 3.72; prepubertal heifers: 12.4 ± 3.19). The cleavage rate was similar between age categories; however, cows tended (p < 0.07) to produce a larger number of blastocysts (9.74 ± 2.26) per OPU than calves (5.57 ± 1.99) and prepubertal heifers tended to have a higher blastocyst yield (35.4%) than calves (27.1%) (p < .07). The expression levels of IGFBP2 and caspase‐3 were higher in oocytes derived from calves compared to the other two categories. The pregnancy rate was higher in calves (43.1%) and cows (40.4%) than in prepubertal heifers (33.8%) (p = .03). Despite the larger numbers of follicles and viable oocytes in cows, the blastocyst production results and pregnancy rates obtained indicate that the use of young females as oocyte donors in IVEP is feasible and may contribute to reduce the generation interval.
Residual feed intake (RFI) is one of the main tools used to identify feed efficiency. However, there is no consensus on the true impact of RFI on male reproductive traits in cattle. The study aimed to evaluate characteristics of the testicular parenchyma and vascular parameters of the pampiniform plexus obtained by ultrasound, semen quality parameters, and sperm freezability in Nellore bulls classified based on RFI. Twenty-seven bulls (21.82±0.88 months of age) evaluated for feed efficiency were sampled for the study, including 15 with low RFI (-0.592±0.09 kg dry matter/day) and 12 with high RFI (0.792±0.10 kg dry matter/day). In ultrasound and Doppler assessment, the most efficient animals (low RFI) showed higher pulsatility and resistive indexes, as well as a tendency (P=0.061) towards greater heterogeneity of the testicular parenchyma (0.625±0.032 vs. 0.508±0.032; 1.012±0.072 vs. 0.802±0.072 and 12.9±0.96 vs. 10.2±0.96, respectively, for low vs. high RFI). However, these animals tended (P=0.0652) to have lower peak diastolic velocity (5.19±0.50 for low RFI vs. 6.54±0.50 for high RFI). Analysis of fresh semen showed a lower percentage of minor defects in low RFI animals (2.67±1.19%) compared to high RFI animals (8.10±1.19%), without differences in the other parameters in fresh or thawed semen and after thermoresistance testing. Evaluation of flow cytometry parameters showed a higher quality of mitochondrial respiration in semen samples of low RFI animals (22.04±2.50%) compared to high RFI animals (12.29±2.71%). In conclusion, although RFI exerts an effect on the Doppler parameters of the pampiniform plexus, it was not sufficient to affect the quality of fresh or thawed semen.
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