Phenotypic evaluations of antral follicles number and correlation with age at puberty in Nellore heifers

• Grant number: 25/08449-4
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: July 01, 2025
• End date: June 30, 2027
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Animal Reproduction
• Principal Investigator: Sarah Figueiredo Martins Bonilha
• Grantee: Marcelo Sant Ana Borges
• Host Institution: Instituto de Zootecnia. Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Nova Odessa , SP, Brazil
• Associated research grant: 21/11922-2 - Science Center for the Development of Climate Neutrality for Beef in Tropical Regions, AP.CCD

Abstract

Age at puberty has a major impact on productive, reproductive and economic efficiency in female beef cattle. The onset timing of this physiological event affects the animal's growth and development rate, in order to support the endocrinological mechanisms that result in puberty and sexual maturity. The occurrence of puberty in females is the end of a series of events that result in ovulation, accompanied by estrus and normal luteal function. Despite the importance of this characteristic, the metabolic signals that activate the endocrine mechanisms that trigger puberty are still poorly understood. In beef cattle, the discovery of a heritable phenotype that explains part of the genetic variation in fertility is extremely important for the selection of more fertile females, in addition to being useful as a biomarker to identify those that should be retained in herds, and also for the development of new selection criteria for fertility. Another challenge is to measure this phenotype in a large number of animals under extensive conditions that characterize tropical beef production. The development of antral follicles in cattle is a complex multifactorial process, with different levels of control, including endocrine and local. Antral follicles can be easily identified by ultrasonography in cattle and can be used to accurately predict ovarian reserve early in life, however, few studies report their relationship with age at puberty. In addition to antral follicles, other measures have been related to fertility, such as anti-mullerian hormone concentration, vulvar, uterine and ovarian biometry. Reproductive performance traits are controlled by many alleles, each with a small effect. Genome-wide association studies (GWAS) have been performed to detect associations between phenotypic traits and allele frequencies of single nucleotide polymorphisms (SNPs), contributing to elucidate the genetic architecture of these traits through heritability estimates. Several GWAS for female fertility traits have been performed, but without identifying regions with a significant effect on these traits. This study aims to evaluate different phenotypes to identify precocious heifers in production systems, in addition to exploring the phenotypic relationship between antral follicle count, age at puberty and fertility, and to perform genome-wide association studies of antral follicle count and age at first corpus luteum using SNP markers, allowing the identification of biomarkers. The results of the integration of biomarkers with genomic analyses are expected to provide promising results regarding the nature of reproductive performance traits, making breeding programs even more efficient and consolidated. (AU)