Genetic disorders in Holstein cattle are a health problem that has grown worldwide in recent years, compromising the sustainability of modern dairy production. In Uruguay, Holstein-based milk production is one of the most important sectors of the country’s economy, but high levels of inbreeding have decreased the breed’s fertility in recent decades. This study investigated the presence and diffusion of lethal and semi-lethal alleles causing embryo death, abortions, fetal malformations, and neonatal diseases in Holstein calves. Using the GeneSeek® Genomic Profiler™ Bovine 50K BeadChip, we genotyped 383 calves (1-30 days-old) from 27 farms located in the main dairy region of Uruguay. Results showed a high prevalence of farms (85%) and carrier calves (21%), including one or more of the following semi-lethal or lethal alleles: Syndactylism (4.18%), brachyspina (3.39%), cholesterol deficiency haplotype (2.61%), complex vertebral malformation (2.09%), bovine leukocyte adhesion deficiency (1.04%s), and Holstein haplotypes HH1 (4.44%), HH3 (3.13%), HH4 (1.04%), and HH5 (0.26%). Most of these alleles had not been recognized previously in Uruguay. We concluded that lethal and semi-lethal mutations are widespread in the Holstein breed in Uruguay. More studies are required to determine their impact on dairy cattle fertility.

Hypotrichosis congenita is a significant disease in Hereford cattle in Uruguay and has been reported worldwide. However, the causal mutation KRT71 has only been recently identified. This communication describes the clinical, histopathological, trichographic, and genetic findings of KRT71-hypotrichosis congenita observed in Hereford calves from two commercial farms. Five affected newborn calves, born in a herd of 15 purebred Polled HF cows, were examined in Farm 1, and one weaned calf in Farm 2. Skin biopsies for histopathology, hair samples for trichogram, and blood samples for genotyping were obtained from affected and control calves and the sire bull and mother cows. Affected animals exhibited a light brown coat with sparse, thin, curly or woolly haircoat. Hypotrichotic skin was dry, erythematous, and scaly. Trichogram analysis revealed thin, fragmented, curly hairs with irregular macro-melanosome groups. The main histopathological findings included marked follicular dysplasia with vacuolation, abnormally large trichohyaline granules in Huxley’s layer, and multiple melanin aggregates in hair fragments, matrix cells, and dysplastic follicles. There were no histological lesions of dermatitis. DNA analysis confirmed that hypotrichotic calves were homozygous for the KRT71 mutation, while one control calf, the bull, and cows in Farm 2 were heterozygous carriers. In conclusion, hypotrichosis congenita in Hereford cattle due to the KRT71 mutation is a color dilution follicular dysplasia.

Uruguay sustains an extensive, pasture-based beef industry with more than 11 million cattle, dominated by Hereford and Aberdeen Angus breeds. Despite their economic importance, inherited disorders are often underreported because most associated losses occur prenatally, thus escaping routine postnatal detection (iceberg effect). This review synthesizes decades (1996-2025, 30 years) of veterinary surveillance and summarizes the clinicopathological features and population impact of hereditary diseases confirmed in Uruguay through integrated pathology and molecular testing. In Hereford cattle, we describe maple syrup urine disease (OMIA 000627-9913), congenital hypotrichosis (OMIA 002114-9913), epidermolysis bullosa simplex (OMIA 002081-9913), cardiomyopathy with woolly haircoat (OMIA 000161-9913), mandibulofacial dysostosis (OMIA 002288-9913), and idiopathic epilepsy (OMIA 000344-9913). In Aberdeen Angus, we detail osteopetrosis (OMIA 000755-9913), neuropathic hydrocephalus (OMIA 000487-9913), dwarfism (OMIA 001485-9913), syndactyly (OMIA 000963-9913), and arthrogryposis multiplex congenita (OMIA 002135-9913). These disorders exert a significant negative impact on reproductive efficiency and may represent a major hidden cause of the country’s consistently low weaning rates. This study highlights the need for systematic genomic surveillance to prevent the dissemination of genetic defects and to safeguard productivity, animal welfare, and the international reputation of Uruguay’s beef herds.