GENOMIC ASPECTS OF SEXUAL PRECOCITY AND INBREEDING EFFECT ON PRODUCTIVE AND REPRODUCTIVE TRAITS IN NELORE CATTLE

RESUMO

.

ABSTRACT

In beef cattle breeding programs, the study of reproductive traits in females is of great importance to meet the growing demand for meat in the world. Currently, strategies are being created that contribute to increasing the genetic gain of productive and reproductive traits, which may lead to the use of a small group of reproducers, which may increase inbreeding levels in populations. The aim of this study was (i) to identify genomic regions and biological factors that affect the heifer early calving (HC) at 24 (HC24), 26 (HC26), 28 (HC28), and 30 (HC30) months of age in Nelore cattle and (ii) to estimate inbreeding coefficients based on pedigree and genomic data on traits of economic interest. A total of 66,496 phenotypic records and 8,652 heifer genotypes for the HC24 - HC30 study were used. For the inbreeding study, 22,680 genotypes were used, the traits studied were adjusted scrotal circumference at 365 days (SC365), HC30; adjusted body weight at 210 (BW210) and 450 (BW450) days of age, ribeye area (REA); backfat thickness (BFT) and rump fat thickness (RFT). The w-ssGWAS results pointedout shared and specific window regions for HC at different ages, which varied according to their genetic correlation. These regions house key genes in the biological process of hormonal, lipid, and metabolic regulation, essential for developing bones, muscles, and reproductive organs. A total of four regions of shared windows between HC24, HC26, HC28, and HC30 were identified in BTA 5, 6, 14, and 16 harboring candidate genes with a direct effect on processes related to the control of functions associated with metabolism, endocrinology, reproduction, and aspects of growth (IGF1, UBA6, GNRHR, LYN, MOS, PLAG1, ETNK2, KISS1, and REN). The average inbreeding depression was -0.241% and -1.102% per 1% of inbreeding for linear regression coefficients scaled on the percentage of mean (m) and standard deviation (sd), respectively. The means for m (and sd) were -0.18% (-1.271%) for sexual precocity traits(SC365 and HC30); -0.37% (-0.985%) for carcass traits (REA; BFT and RFT) and -0.17% (-1.051%) for weight traits (BW120 maternal and animal and BW455). Findings showed differences in physiological processes linked to HC at different ages and metabolic processes that help the genetic control of sexually precocious Nelore heifers. Hence, inbreeding depression is more pronounced in carcass traits than in sexual precocity and weight traits. These findings highlight the need for the management of inbreeding in the breeding programmes. For all traits, long and short ROH contributed to inbreeding depression. The results obtained from inbreeding depression will allow establishing that they allow monitoring and maintaining genetic diversity, which will improve the traits that are part of the genetic improvement program of the Nelore breed.