Morphological defects in Nellore cattle, including abnormalities in conformation, feet and legs, navel structure, pigmentation, and craniofacial development, negatively impact productivity, welfare, and long-term herd sustainability. This comprehensive review aimed to synthesize existing genetic and genomic evidence on these defects in purebred Nellore cattle. Studies were identified through searches of Web of Science, PubMed, and SciELO up to September 2025. Eligible studies included genetic or genomic analyses of morphological defects in purebred Nellore cattle. The methodological characteristics and limitations of the included studies were evaluated descriptively. Results were synthesized using a narrative descriptive approach due to heterogeneity in phenotypes and methodologies. A total of 89 studies were included. This review summarizes phenotype definitions and scoring systems (e.g., MES, EPMURAS, MERCOS) used in breeding programs. Most reported heritability estimates ranged from approximately 0.10 to 0.68 across traits and analytical scales, with liability-scale estimates for binary defects reaching 0.54 for depigmentation. Genetic correlations with growth traits were generally favorable or weak, whereas evidence regarding reproductive traits was limited and less consistent. Linear models are widely used to analyze morphological defects but may underestimate genetic variance for categorical and unbalanced traits, whereas threshold models offered improved theoretical suitability at higher computational cost. Key limitations across studies included evaluator subjectivity, imbalanced score distributions, limited phenotypic granularity, and environmental heterogeneity. Morphological defects show sufficient genetic variability to support inclusion in genetic evaluations. Standardized phenotyping protocols, improved scoring strategies, and expanded genomic analyses are needed to enhance selection accuracy and animal welfare in Nellore cattle.

Most studies involving genomic data in animal breeding use only the effects of autosomal chromosome markers, excluding the sex chromosomes. However, the X chromosome is the second-largest chromosome in the bovine genome, and several economically important traits are sexually dimorphic, such as those related to growth. Therefore, the objective of this study was to evaluate whether there are predictive advantages for genetic parameters when including genomic markers from the X chromosome for yearling weight (YW) and postweaning gain (PWG) in Nellore cattle. Genetic parameter estimates were obtained under three scenarios: (1) only pedigree and phenotypic information; (2) pedigree, phenotypes, and autosomal chromosome markers; and (3) pedigree, phenotypes, autosomal chromosome markers, and X chromosome markers. Analyses were carried out using Bayesian inference with BLUPF90 family software version 2025. The heritability estimates obtained and their respective standard errors were 0.41 ± 0.004 for YW and 0.21 ± 0.004 for PWG. No differences were observed among the three scenarios tested for either trait. Therefore, the inclusion of the X chromosome did not influence the estimates of genetic parameters for these growth traits in Nellore cattle. Nevertheless, further molecular and genomic studies on the bovine X chromosome are still needed to explain the genetic effects and biological functions associated with this chromosome and with different traits of economic interest, as well as to justify whether to include the X chromosome in genomic prediction analyses.