Genomic confirmatory factor analysis on milk fatty acid profile in dairy cattle reared in tropical conditions

• Autor(a) principal: Dauria, Brayan Dias
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11139/tde-25052021-133628/
• topic: Ácidos graxos; Bovinos leiteiros; Dairy cattle; Estresse térmico; Fatty acids; Heat stress; Latent variable; Variável latente

The bovine milk fatty acid (FA) profile is one of the most complex and unique among terrestrial mammals. Its composition is extremely variable and depends on factors such as the source of the diet, the physiological state of the animal, and a fraction attributed to the genetic component. FA is mainly synthesized by the new synthesis that occurs in the mammary gland or derived from the ruminal biohydrogenation process. Recently, efforts have been made in an attempt to elucidate the main mechanisms associated with their metabolic pathways. In addition, the FA profile has been investigated as a biomarker for heat stress due to the great influence of diet on its composition. Most of these studies are carried out by analyzing genetic parameter estimation, genome-wide association study (GWAS), and in a complementary tool with enrichment analysis. However, little has been explored on approaches that can assess quantitative characteristics in a multivariate method. In this context, two studies were conducted using different strategies and objectives. The objective of this study was to estimate the genetic parameters for FA under conditions of thermal stress (decline) and without thermal stress (intercept), subsequently to compare genomic values between rankings (intercept and decline). Records of test-day milk of 7 FA (saturated FA - SFA, unsaturated FA - UFA, monounsaturated fatty acid - MUFA, polyunsaturated FA - PUFA, palmitic FA - C16:0, oleic FA - C18:0, and stearic FA - C18:1) were used in genetic analysis. The components of variance were obtained using a repeatability model with random regression of a THI function (temperature and humidity index). Saturated FA (saturated and C16:0) showed lower estimates of heritability under thermal stress conditions. C18:1 showed greater sensitivity to heat under conditions of thermal stress. Correlations between the rankings of genomic genetic values ranged from -0.27 to 0.99. Our results demonstrated an opportunity to investigate new biomarkers and improve selection processes for thermotolerance. In experiment 2, the objective was to adjust latent variables (unobservable variable) and predict factor scores to use them as a phenotype in the estimation of genetic parameters, GWAS, and enrichment analysis. The adjustments were obtained through confirmatory factor analysis (multivariate method) whose main objective is to reduce the size of the data. The set of observable variables that obtained the best fit in the model were SAT, POLI, C18: 0, and C18:1. These variables were combined into a factor that represented 3 stages of lactation (40-60; 160-180; 250-270), based on fixed intervals in days in milk (DIM) and later, were merged to represent lactation order (1 to 3) used in genetic analysis. The heritability estimates for latent variables were low (0.07 to 0.11). From the GWAS results, 11 candidate genes (PLD1, TM6SF2, NUDT7, LIPT1, AKPA1, APOH, RPGRIP1L, FTO, GMDS, ALDH3B1, and PC) were located on 9 chromosomes, mostly including genes that have not yet been discussed in the literature. In the enrichment analysis, functional terms were revealed including fatty acid synthesis, triacylglycerol synthesis, and lipid and lipoprotein metabolism. Overall, our study contributed as a design for further studies and to improve the knowledge base on the genetic mechanisms underlying the composition of FA.