Genetic Parameters and Genome-Wide Association Analysis of Reproductive and Calving Traits in Jersey Cattle.

This study characterized the genetic basis of reproductive and calving traits in Jersey cattle at different physiological stages and identified potential candidate genes. After quality control, 2716 records were available for heifer reproductive traits, 2707 for multiparous cow reproductive traits, and 5423 calving records for calving ease (CE) and calf birth weight (CBW). CE and CBW were analyzed from the maternal perspective, with records assigned to the corresponding dams. Genetic parameters were estimated using AI-REML in DMU with animal, repeatability, and bivariate models. Genome-wide association analyses were performed using a mixed linear model based on 1,660,477 SNPs from 1578 genotyped Jersey cattle. Heritability estimates for age at first service (AFS) and age at first calving (AFC) were 0.416 and 0.380, respectively, whereas estimates for reproductive traits in multiparous cows were generally low (0.072-0.154). Calving interval (CI) and days open (DO) showed a strong positive genetic correlation (0.781). GWAS identified five significant loci associated with AFC, number of services per conception in heifers, CI, and dam-associated genetic variation in CE. Candidate genes included PIK3C2G, DGKI, ABCC1, CCDC85A, CRMP1, EVC, and EVC2. Exploratory KEGG enrichment suggested potential involvement of phosphatidylinositol signaling, Hedgehog signaling, ABC transporters, and inositol phosphate metabolism. Overall, reproductive traits showed distinct genetic characteristics between heifers and multiparous cows, and AFS and AFC exhibited relatively greater potential for genetic improvement. The identified genomic regions provide preliminary candidates for further validation and potential future application in genomic breeding.