Effect of age and scrotal circumference on sperm morphology in Brahman bulls using a modified fixation technique

Francisco Sevilla^1,2Ignacio Araya-Zúñiga^2,3Arcesio Salamanca-Carreño⁴Miguel Ángel Silvestre⁵Julio Rodríguez⁶Kenneth Matamoros²Rafael Molina-Montero⁶Luis Carranza²Eduardo R. S. Roldan⁷Anthony Valverde^2*

• ¹Instituto Tecnológico de Costa Rica, Universidad Nacional, Universidad Estatal a Distancia, Doctorado en Ciencias Naturales para el Desarrollo (DOCINADE). Alajuela, Costa Rica, Alajuela, Costa Rica
• ²School of Agronomy, San Carlos Campus, Costa Rica Institute of Technology, Alajuela, Costa Rica
• ³Instituto Tecnológico de Costa Rica, Área Académica del DOCINADE, Maestría en Ciencia y Tecnología para la Sostenibilidad, Alajuela, Costa Rica
• ⁴Cooperative University of Colombia, Faculty of Veterinary Medicine and y Zootechnics, Villavicencio, Colombia, Villavicencio, Colombia
• ⁵Universitat de València, Departament de Biologia Cellular, Biologia Funcional i Antropologia Física, Campus Burjassot, C/Dr. Moliner Burjassot, Spain, Valencia, Spain
• ⁶Costa Rica Institute of Technology, School of Agronomy, Agricultural Production Program (PPA), San Carlos Campus, Alajuela, Costa Rica, Alajuela, Costa Rica
• ⁷Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain, Madrid, Spain

Sperm morphology (form and size of sperm) analysis is useful for evaluating bull fertility and diagnosing reproductive fitnessperformance. An advanced age is associated with a higher frequency of morphological sperm anomalies; however, there is limited information on the effect of aging and scrotal circumference on sperm morphological defects in Brahman cattle. The objective of this study was to investigate changes related to age and scrotal circumference on sperm morphology in Brahman bulls in Costa Rica. Brahman bulls are traditionally used in Costa Rican production systems. Sperm morphology was evaluated in 41 51 Brahman bulls from six age groups (< 24, 2524-36, 37-48, 49-60, 61-72, and > 72 months old) and scrotal circumference (32-36, 37-41, 42-46, and > 47 cm). The Trumorph ® systems Trumorph Systems wereaswas used for fixation. A total of 82 112 ejaculates and two hundred sperm cells were analyzed per sample. Sperm defects were classified according to the 2021 World Health Organization laboratory manual and classification of University of Queensland Sperm Morphology Standardization Program. There was a higher frequency of anomalies in younger bulls (< 24 months old) and in those with a scrotal circumference greater than 47 cm. A significant variation was found between the years analyzed, with significant differences (p < 0.05) of the year 2022 with respect to the others years. The most common defects by anatomical sperm region were loose heads and nuclear vacuoles, distal midpiece reflex, and bent tails. Deterioration related to age and scrotal circumference was observed in sperm morphology, with a higher defect frequency in bulls under 24 months of age and in those with a scrotal circumference greater than 47 cm. Sperm morphology in Brahman bulls showed similar incidence regardless of sexual status (breeding or resting), but they varied according to age and scrotal circumference.