Genetic regulation of reproduction traits in livestock species The genetic regulation of reproduction traits in livestock species is an important area of study within animal science and genetics. Understanding the underlying genetic mechanisms that control reproductive traits is essential for improving breeding programs and enhancing productivity. These traits are typically complex, influenced by numerous genes, few of which have predominant effects, and are also influenced by environmental factors. Examples of reproduction traits include fertility, litter size, gestation length, and puberty onset. Advances in molecular biology and multi-omics have provided powerful tools to identify the genetic factors that affect reproduction traits. Studies in this subject aim not only to improve the efficiency and sustainability of livestock production but also contribute to animal welfare and the economic viability of the livestock industry. This Research Topic encompasses seven articles highlighting different Research Topic currently being studied, summarized below, offering valuable insights into this field. Jia et al., studied the egg-laying in a Chinese local breed, Wuhua yellow-feathered chicken. This trait is strongly associated with chicken follicle development, which is controlled by the gonadal axis of the reproductive endocrine system. During this process RNA modifications, such as in RNA N6-methyladenosise (m6A), occur. These authors conducted a transcriptome-wide m6A methylation analysis of Wuhua yellowfeathered chicken ovaries before and after sexual maturation to identify the potential molecular mechanisms underlying chicken ovary development. A positive correlation was observed between the m6A peaks and gene expression levels, indicating that m6A may play an important role in the regulation of chicken ovary development. Functional enrichment analysis indicated that apoptosis-related pathways could be the key pathway underlying the poor reproductive performance of Wuhua yellow-feathered chicken. Follicular atresia is the process through which ovarian follicles degenerate and are reabsorbed before reaching maturity. This is a natural part of the ovarian cycle and occurs throughout a female's reproductive life. Studies have shown that miRNAs influence the follicular atresia by post-transcription regulation. Liu et al., performed a high-throughput small RNA sequencing to analyze differential miRNA expression profiles between healthy (HF) follicles and early atretic (EAF) follicles. A total of 237 conserved miRNAs were

Beef cow reproductive traits are critical for system profitability and difficult to improve using selection. A custom array with 131 SNPs identified within genes related to cow puberty and fertility was evaluated in privately owned Angus (A), Charolais, Brangus, and Red Brangus cows in México (n = 828) and in A, Brahman (B), Hereford (H), Nellore (N), and crossbred (F₁ and F₂ B-H, F₂ B-A, first- and second-generation 3/8 B 5/8 A, and 3/8 N 5/8 A) cows in a Texas research herd (n = 449). Cow traits included age at first and second calving, calving interval, and reproductive success. Calf traits were birth weight and occurrences of calving difficulty, calves with inadequate vigor at birth, and mortality. Residuals from fixed effect models were used in association analyses. The detection of associated loci was mostly within combined groups. A marker in RHEBL1 was associated (p < 0.05) with age at calving in Angus. A locus in FAM19A4 was associated (p < 0.05) with reproductive success in Brangus and inadequate calf vigor in all data combined. Markers in SYCE1 and CPNE5 were associated (p < 0.05) with reproductive success and calf mortality in Bos indicus. Functional panels may be more effective when designed for individual breeds or sub-species.