The aim of this study was to estimate genetic parameters and to identify genomic regions associated with the calving ease (CE) in precocious Nellore heifers. A total of 1,277 CE phenotypes were collected and scored into two categories: i- non assisted calving, categorized as success (1) and ii- assisted calving where heifers required any form of assistance or intervention to give birth, categorized as failure (2). A pedigree structure containing the identification of the animal's sire and dam was used, with the relationship matrix comprising a total of 6,511 animals. Genotypic data from 1,201 animals were obtained using low-density panel (Clarifide Nelore 3.1) encompassing over 29,001 single nucleotide polymorphisms (SNP) markers. A threshold sire-maternal grandsire model (S-MGS) was used to estimate the genetic parameters, which included sire, maternal grandsire and residual effects as random effects and the fixed effects of contemporary groups (farm and year of calving, sex) and birth weight of the calf as covariable (linear effect). Genomic breeding values were estimated using an animal model with the direct and maternal genetic variances which were previously obtained by means of a S-MGS threshold model. The direct and maternal heritability estimates for CE were obtained considering the covariance of direct and maternal effects fixed as zero. Regions that accounted for more than 0.5% of the additive genetic variance were used. The direct and maternal heritability estimates for CE were low (0.18) and moderate (0.39) respectively, indicating that genetic progress for this trait is feasible, and so, it would respond favorably to direct selection. Genes identified within the significant windows, such as CA8, FAM110B, TOX, ARID1A, RBM15, HSF1 and PLAG1 were found to be related with maternal and direct effects on CE. Gene enrichment analysis revealed processes that might directly influence fetal processes involved in female pregnancy and stress response. These results should help to better understand the genetic and physiological mechanisms regulating placenta development and fetal development, and this information might be useful for future genomic studies in Nellore cattle.

这项研究的目的是估计遗传参数，并鉴定与早熟Nellore小母牛产犊容易程度（CE）相关的基因组区域。总共收集了1,277个CE表型并将其分为两类：i-非辅助产犊，分类为成功（1）； ii-辅助产犊，小母牛需要任何形式的帮助或干预才能生出，分类为失败（2） 。使用了包含动物的父亲和母亲身份的血统结构，其关系矩阵包括总共6,511只动物。使用包括超过29,001个单核苷酸多态性（SNP）标记的低密度面板（Clarifide Nelore 3.1）获得了1,201只动物的基因型数据。阈值父亲-母亲祖辈模型（S-MGS）用于估算遗传参数，其中包括父亲，产妇的祖父项和剩余效应为随机效应，当代群体的固定效应（农场和产犊年份，性别）和小牛的出生体重为协变量（线性效应）。使用具有直接和母体遗传差异的动物模型来估计基因组育种值，该动物模型先前是通过S-MGS阈值模型获得的。考虑到直接和母体效应的协方差固定为零，获得了CE的直接和母体遗传力估计值。使用占累加遗传方差超过0.5％的区域。CE的直接和母体遗传力估计值分别较低（0.18）和中等（0.39），表明该性状的遗传进展是可行的，因此，它将对直接选择产生有利的响应。发现CA8，FAM110B，TOX，ARID1A，RBM15，HSF1和PLAG1与CE的母体和直接作用有关。基因富集分析揭示了可能直接影响女性怀孕和应激反应的胎儿过程的过程。这些结果应有助于更好地了解调节胎盘发育和胎儿发育的遗传和生理机制，并且该信息可能对将来在内洛尔牛中的基因组研究有用。