Genes candidatos para características de crescimento, reprodução e resistência em bovinos de corte

Abstract

Selecting animals which have favorable alleles in genes that participate in the genetic control of economic interest traits may increase the efficiency of beef cattle breeding programs. In this way, two papers were developed with the main aim of identified functional candidate genes (FCG) for important traits in Nellore cattle. In the first paper, “Genes underlying genetic correlations between growth, reproduction and parasite burden traits in beef cattle”, we aim to estimate genetic correlations between growth, reproduction and parasite burden traits and identified FCG that influence more than one of these traits. We evaluated six traits, comprising two of growth (body weight - BW and average daily gain - ADG), one of reproduction (scrotal circumference - SC) and three parasite burden (counts of tick - TICK, gastrointestinal nematode eggs per gram of feaces - GIN, and Eimeria spp. oocysts per gram of faeces - EIM). The genetic correlations were obtained through multiple trait models. A total of 21,667 SNP markers were used to perform single-step GWAS (Genome Wide Association Studies), and to identify genomic windows that explained at least 1% of the genetic variance for the evaluated traits.

The genetic correlations were positive and of moderate magnitude for the pairs of traits BW- ADG (0.64), BW-SC (0.38), BW-TICK (0.39), ADG-SC (0.27), and TICK-EIM (0.33). Only

the pair ADG-EIM presented a negative correlation (-0.22). For all the other pairs, the genetic correlations were close to zero. The effects of the SNPs were calculated as genetic standard deviation and showed that there were SNPs mapped in FCG that promoted genetic improvement to both traits. Additionally, functional analyses were performed and FCGs were selected based on their roles in biological processes for each trait. The functional analyses selected seven genes, SLC16A4, KCNA2, LAMTOR5, DUSP10, MAP3K1, TPMT, and KIF13A as FCGs with effects over more than one trait. Independently of the genetic correlation (low-moderate) there are FCG that can influence both production, reproduction or resistance traits in beef cattle. In the second paper, “Candidate genes for longitudinal traits under selection in beef cattle”, we

aim to identify functional candidate genes which take part in genetic control of body weight in five different ageS (330, 385, 440, 495 and 550 days) for a beef cattle population for two databases which one with complete body weight records (DB100) and another one which a sequential selection of 70% of heaviest animals (DB70). The genetic parameters for body weight were estimated by a single trait (STM) and a random regression model with spline functions (RRM) for both databases. Body weights were standardized at 330, 385, 440, 495 and 550 days of age for STM. In RRM, the knots of linear splines were fitted at 274, 330, 385, 440, 495, 550 and 594 days of age. The GWAS were performed with both STM and RRM. The GWAS and the functional enrichment were performed as previous described from the first paper. We identified seven FCG (DUSP10, LAMTOR5, PAFAH2, SLC30A2, TRIM63, NCAM1 and SCL16A4) to body weight in different ages. of each gene for animal growth can change in different development stages and different The DUSP10 gene was associated with body weight in all the five ages evaluated, appointing for the relevance of this gene for different stages of the animal growth. On the other hand, the majority of the FCG associated with body weight were different for different ages suggesting that the importance genes can be more relevant to body weight in each growth stage. When the sequential selection was simulated different FCG were associated with body weight in DB100 and DB70 for each age, even when the RRM was performed. Also, when GWAS and post GWAS are performed, the sequential selection influenced the results and this may be one more reason for frequent inconsistences in GWAS results performed for growth traits measured in beef cattle. We suggested genes as FCG which take part in the genetic control of important traits to beef cattle. Therefore, these genes could be validated in largest populations and different breeds, in order to improve the understanding about the genetic control of them over the traits here evaluated.