Somatic cell nuclear transfer (SCNT) is a reproductive biotechnology with great potential in the reproduction of different species of zootechnical interest, including sheep. This study aimed to carry out a bibliometric analysis of scientific papers published on the application of SCNT in sheep reproduction during the period 1997–2023. The search involved the Science Citation Index Expanded and Social Sciences Citation Index databases of the main collection of the Web of Sciences with different descriptors. A total of 124 scientific papers were analyzed for different bibliometric indicators using the VOSviewer software. Since 2001, the number of SCNT-related papers that have been published concerning sheep reproduction has increased and it has fluctuated in ensuing years. The main authors, research groups, institutions, countries, papers, and journals with the highest number of papers related to the application of SCNT in sheep reproduction were identified, as well as the topics that address the research papers according to the terms: somatic cell, embryo, oocyte, gene expression, SCNT, and sheep.

Background: The fertility of the flock depends largely on the male, so the selection of studs with high genetic potential and good semen quality is essential. The frequency of collection directly influences sperm parameters such as volume, concentration, motility, and viability, with variations depending on species and breed. Objective: To evaluate the effects of the number and frequency of ejaculate collection on pre- and post-freezing semen characteristics in Katahdin sheep. Methodology: Fifteen one-year-old males were used, divided into three groups according to collection frequency: high (every 2 days), medium (every 4 days), and low (every 8 days). Semen parameters such as volume, motility, concentration, vitality, and DNA fragmentation were analyzed in both fresh and post-thaw semen. Results: Motility was significantly lower in the high frequency group (67.4 ± 6.5%) compared to the medium (73.9 ± 6.0%) and low (72.3 ± 8.7%) frequency groups (p ≤ 0.05), with no differences between the latter two groups. Sperm concentration decreased in the high frequency group (3001.66 ± 709.7 * 10⁶/mL) compared to the medium (4024.15 ± 595.1 * 10⁶/mL) and low (4035.44 ± 420.7 * 10⁶/mL) frequency groups (p ≤ 0.05). Vitality was lower in the high frequency (72.6 ± 6.5%) compared to the medium (78.6 ± 4.7%) and low (78.3 ± 5.9%) (p ≤ 0.05). DNA fragmentation increased in the second ejaculate of the high frequency group (16.3 ± 4.2%) compared to the medium (11.5 ± 3.7%) and low (10.4 ± 2.8%) frequency groups (p ≤ 0.05). After cryopreservation, motility of the second ejaculate was lower in the high frequency group (39.2 ± 6.3%) compared to the medium (45.7 ± 5.9%) and low (46.3 ± 5.2%) frequency groups (p ≤ 0.05). Implications: High collection frequency reduces semen quality in Katahdin sheep, negatively affecting critical parameters such as motility, concentration, vitality, and DNA stability. Optimizing extraction frequency not only promotes semen preservation and reproductive program efficiency, but also contributes to animal welfare by avoiding excessive collections that compromise semen quality. Conclusion: Collection frequency and number of ejaculates significantly influence semen quality in Katahdin sheep. Too frequent collections decrease sperm motility, concentration, and vitality, in addition to increasing DNA fragmentation, especially in the second ejaculate. Key words: Seminal parameters; Katahdin sheep; DNA fragmentation; cryopreservation.

Somatic cell nuclear transfer (SCNT) is a reproductive biotechnology with great potential in the reproduction of different species of zootechnical interest, including sheep. This study aimed to carry out a bibliometric analysis of scientific papers published on the application of SCNT in sheep reproduction in the period 1997-2023. The search involved the Science Citation Index Expanded and Social Sciences Citation Index databases of the Main Collection of Web of Sciences with different descriptors. A total of 124 scientific papers were analyzed for different bibliometric indicators using VOSviewer software. Since 2001, the number of SCNT-related documents published concerning sheep reproduction increased and has fluctuated in ensuing years. The main authors, research groups, institutions, countries, documents and journals with the highest number of publications related to SCNT in sheep reproduction were identified, as well as the topics that address the research papers according to the terms: somatic cell, embryo, oocyte, gene expression, SCNT, and sheep.

The bighorn sheep is listed on the IUCN Red List of Threatened Species. By interspecies somatic cell nuclear transfer (ISCNT), other endangered species are cloned using somatic cells as nuclear donors, fusing them with enucleated oocytes from heterologous domestic species. On the other hand, resveratrol added during in vitro maturation (IVM) of domestic sheep oocytes favors the development of embryos produced in vitro. The aim of this study was to treat O. aries oocytes with resveratrol during IVM using them as cytoplasts in ISCNT via handmade cloning (HMC), evaluating its effect on the in vitro development of Mexican bighorn sheep (O. c. mexicana) cloned embryos. Post-mortem skin fibroblasts from an adult male specimen from the Chapultepec Zoo were frozen for 8 years, thawed, and reseeded for 8 cell passages. For IVM, O. aries oocytes were treated with 0, 0.5, or 1.0 µM resveratrol. Matured oocytes were manually enucleated, and triplets (O. aries cytoplast-O. c. mexicana karyoplast-O. aries cytoplast) were formed and electrically fused. The reconstructed embryos were chemically activated and cultured until they developed into blastocysts. For IVM, no differences were found between treatments, yet at 0.5 µM, resveratrol significantly increased (p<0.05) the blastocyst rate and decreased the fragmentation rate.

The aim of this study was to treat sheep oocytes with resveratrol during in vitro maturation (IVM) and use them as cytoplasts in ISCNT via handmade cloning (HMC), evaluating the effect of resveratrol on the in vitro development of cloned Mexican bighorn sheep embryos. Post mortem skin fibroblasts from an adult male specimen were frozen for 8 years, thawed, and reseeded for eight cell passages. For IVM, Ovis aries oocytes were treated with 0, 0.5, or 1.0 µM resveratrol. Matured oocytes were manually enucleated, and triplets (O. aries cytoplast–Ovis canadensis mexicana karyoplast–O. aries cytoplast) were formed and electrically fused. The reconstructed embryos were chemically activated and cultured for in vitro development (IVD). The IVM rate was 81.8 ± 10.4% for CG, 81.9 ± 6.7% for EG1, and 76.3 ± 7.7% for EG2, with no significant differences between groups. For IVD, EG1 showed a statistically significant increase (p < 0.05) in the blastocyst rate (31 ± 12.0%) and a statistically significant decrease in the fragmented embryo rate (25 ± 10.4) when compared with the other groups. It was concluded that better rates of cloned bighorn sheep blastocysts could be obtained in ISCNT via HMC when fusing O. aries oocytes supplemented with resveratrol during IVM with post mortem adult male O. c. mexicana fibroblasts that had been cryopreserved for 8 years.