Arquitetura genética do holobionte Nelore (Bos indicus): implicações em fenótipos de desempenho e de temperamento

Abstract

Beef cattle production is one of the main pillars of Brazilian agribusiness, with emphasis on the Nelore breed (Bos indicus), which is widely adapted to tropical conditions. Despite advances in genetic improvement, productive and temperament traits exhibit low to moderate heritability, indicating that the phenotypic variation of these traits is not fully explained by host genetics. In this context, the gastrointestinal microbiota has been recognized as an important modulator of metabolism, feed efficiency, productive performance, and behavior-related traits in ruminants. The interaction between host genetics and the microbiome constitutes a relevant component in the expression of complex phenotypes, with microbiability being used as a complementary measure to genetic heritability. However, its application in beef cattle, particularly in Nelore populations, remains limited. Thus, this thesis aimed to investigate host-microbiome interactions in Nelore cattle, evaluating the influence of host genetics on the fecal microbiota and its associations with performance and temperament traits in young bulls. For this purpose, 16S rRNA gene sequencing was performed for taxonomic characterization of the fecal microbiota, integrated with host genomic information. Associations between microbial features and performance traits were evaluated using linear mixed models, whereas host-microbiome interactions were investigated using genomic linear mixed models and hierarchical Bayesian models to estimate the heritability of microbial features, identify host genetic variants through genome-wide association studies (GWAS), estimate heritability and microbiability of performance and temperament traits, and evaluate genetic and microbial correlations. Significant associations were identified between elements of microbial composition and phenotypes, including ribeye area, metabolic weight, and EPMURAS, highlighting the role of the microbiota in animal performance. Additionally, a portion of microbial abundance features exhibited measurable heritability, with the identification of genetic variants associated with the microbiota and candidate genes potentially involved in host-microbiome interactions. Heritability estimates were moderate to high, indicating a strong influence of host genetics on the evaluated phenotypes. In contrast, microbiability showed low magnitudes, although with a relatively higher contribution to some traits related to feed intake, morphology, fat deposition, and temperament. Furthermore, the microbiota influenced associations among temperament phenotypes, showing correlation patterns distinct from those observed for host genetic effects. Overall, the results obtained enhance the understanding of interactions between host genetics and the microbiome in beef cattle, indicating that the microbiota may act as a complementary component of phenotypic variation and be incorporated into genomic evaluation models, contributing to more efficient and sustainable genetic improvement strategies.