Genetic and genomic insights into morphological defects in nellore cattle: a comprehensive review

Abstract 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.