The calving interval (CI) can be defined as the period (days or months) between the birth of a calf and the birth of a subsequent calf, both from the same cow [1]. Some previous studies have reported high CI values for Nellore cattle, for instance, 648.9 ± 321.2 days for Nellore cows in northeastern Brazil [2]. Reducing CI is one of the major concerns of breeders because the accumulated productivity of Nellore cows has a genetic correlation ranging from −0.16 to −0.40 with CI values [3]. Moreover, the CI of Nellore cattle has increased over generations [4]. Previous economic analysis also showed that CI was more important than feed efficiency in Nellore cattle [5], and several economic studies over the last decades reported that improving reproductive traits, such as CI, increases the efficiency of the cattle production system [6]. In addition to increasing cow productivity, a shorter CI improves the selection intensity and reduces the generation interval [7].

Previous studies with different cattle breeds reported low heritability estimates for CI, and a meta-analysis of these results found a low weighted heritability (0.02 ± 0.02) for CI [8]. The studies with Nellore cows also reported small heritability for CI, such as 0.09 [9] and 0.05 ± 0.01 [10]. Therefore, CI is strongly influenced by environmental factors, and a small genetic gain is expected by selection. Despite this, genomic data can help understand the genetic architecture of complex traits such as CI.

The genome-wide association study (GWAS) can contribute to identifying variants associated with complex traits in livestock [11]. GWAS analysis uses single nucleotide polymorphisms (SNP) distributed throughout the genome, phenotype, and pedigree information to identify associations between genotype and phenotype [12]. Furthermore, it allows the discovery of new genes associated with complex traits and, consequently, expands knowledge about the genetic control of these traits. In Beef cattle, CI was a goal of GWAS analysis carried out for Limousin and Charolais, and significant SNPs were found on the BTA3 and BTA2 [6]. In Holstein dairy cows, three genomic windows (BTA3, BTA6, and BTA7) were associated with CI [13], while variants in BTA2, 5, 8, 24, and 28 were also reported [14]. However, GWAS analysis for CI was not carried out for Nellore cattle or any other Bos taurus indicus breed. Therefore, this study aimed to carry out a GWAS analysis for the first CI of Nellore cows to identify genomic regions associated with this complex trait. Moreover, a functional annotation study was also performed for the QTLs and genes near the areas where SNPs associated with CI were found.