Seleção genômica para peso ao nascimento e período gestacional em bovinos da raça girolando

Abstract

Milk production plays an essential role in Brazilian agriculture, but is subject to several variables, from climate to macroeconomic factors. Girolando breed animals represent the vast majority of national dairy production due to their adaptability to challenging environments. However, dairy farming often faces adverse conditions, which requires a closer look at reproductive traits, such as calving ease. This essential trait has a significant impact on animal production, fertility and welfare, making it worthy of genomic analysis. The objective of this study was to perform genomic validation for calf birth weight (BW) and dam's gestational length (GL) traits in a population of Girolando cattle. A data file provided by the Programa de Melhoramento Genético da Raça Girolando (PMGG) was used, consisting of records of BW and GL of 83,097 animals, including pure Holstein (H) and Gyr (G), and Girolando with six different breed compositions: 1/4H + 3/4G, 3/8H + 5/8G, 1/2H + 1/2G, 5/8H + 3/8G, 3/4H + 1/4G, 7/8H + 1/8G. The records underwent strict quality control, excluding values outside specific ranges. Statistical analysis was performed using RStudio software and included analysis of variance (ANOVA) and orthogonal contrasts to evaluate the impact of different factors, such as sex, gestational length and method of conception, on the variables of interest, as well as the influence of the animals' breed composition on these variables. Genetic evaluation of the animals for the traits under study was conducted using the traditional BLUP and single-step genomic BLUP (ssGBLUP) methods in single-trait analyses, and the efficiency of using genomic information in predicting genomic breeding values (GEBVs) was compared. After the contrast of means analyses, no statistically significant differences were identified in the BW and GL traits of Girolando breed animals in relation to factors such as sex, method of conception, measurement method, and breed composition. It was found that the inclusion of genomic data in the genetic evaluation for BW and GL contributes to a better estimation of the Genomic Predicted Transmitting Ability (GPTA) and the accuracy for Girolando animals, especially for animals without available phenotypes for analysis. The comparative analysis between genomic evaluations (GEBV) and traditional ones (EBV) highlighted the importance of genotyping and phenotyping, with higher precision in estimates when both types of data are available, allowing for a better differentiation of animals with superior genetic merits to facilitate calving. Significant increases in accuracy were achieved, reaching 0.83 for BW and 0.88 for GL with genomics. These results indicate that the genomic approach can accelerate genetic progress in Girolando breed improvement programs compared to traditional methods. This underscores the importance of considering data availability and context when using genomic methods in animal breeding.