Genome-wide association study for reproduction traits in a Brazilian Holstein population

Abstract

Genome-wide association study for reproduction traits in a Brazilian Holstein populationBrazil is in an important position in the world of the dairy productive chain, and the efficiency of the production has been discussed in different fields in this chain, among those, reproductive efficiency. Studies on improvement for better comprehension of the management, dietary intake, sanity, and genetic terms, have been applied to comprehend ways to optimize dairy production and turn it more and more profitable for the producer. Reproductive phenotypic characteristics such as age at first calving (AFC), calving interval (CI), and quantity of inseminations needed to impregnate the cow are parameters for understanding and monitoring the reproductive activity of a herd. The ideal is that the cow is as precocious and has the smaller calving interval as possible. It is known that reproductive characteristics have low heritability, undergoing great environmental influence. In this line, it is necessary to know the genes that are involved in this process to have more and more clarity. With genomic association studies and advances in molecular biology, it is possible to explain the genetic background of these characteristics and with the use of molecular markers, we find regions responsible for the origins of the biological variation that show us these characteristics. Thus, this study aimed to identify genomic regions associated with age at first calving (AFC), to calving interval (CI), in a population of Holstein cattle. To identify regions that possibly alter the phenotype, GWAS was applied to the database of phenotypic data of AFC, IC of 39,336 daughters, and genotype of 555 bulls, in 187 different herds, contemporary groups were formed and analyzed in GWAS. Data underwent quality control and by the end, there were 75,925 SNPs. BLUPF90 family software was used for statistical analysis and known pedigree animal model, with 10 SNPs fixed windows, and explained variance over 1.5%. A total of 34 genes were identified: 24 genes linked to AFC and 10 genes linked to CI. The main genes were APP, PRSS16 e BTN1A1, once linked to the animal immune response to the postpartum intemperance and to the reproductive system recovery. The genes CYYR1, PRSS16 e WEE2 are known to be related to embryogenesis, linking them to the reproductive traits of the animals. Some of the identified genes, in the present study, were associated with reproductive and immunological characteristics of the animals, corroborating the hypothesis of a different genetic expression among the investigated animals, and indicating the need for the development of new studies in this field.