Prevalence and Morphological Appearance of Sperm Nuclear Defects Using Feulgen Reaction in Beef Bulls

The objective of this study was to assess the prevalence and compare the morphological aspects of sperm nuclei abnormalities in beef bulls submitted to breeding soundness evaluation (BSE). Semen samples were collected by electroejaculation from 649 beef bulls (Bos indicus, n = 515 and Bos indicus × Bos taurus crossbreed, n = 134) ranging from 2 to 12 years of age. Following a clinical evaluation and semen assessment, a slide was prepared with fresh semen and stained by using the Feulgen-stain for the purpose of evaluating sperm and nuclear morphology. Abnormal sperm nuclei were classified into three categories: A, multiple vacuoles in a pouch-like formation; B, a single vacuole such as the nuclear crater/diadem defect; and C, abnormal chromatin condensation. In accordance with the BSE criteria, the animals were classified as either satisfactory or unsatisfactory potential breeders. The prevalence of nuclear defects was comparable between satisfactory bulls of both genotypes. Unsatisfactory Bos indicus bulls exhibited a higher frequency of A and B nuclear defect categories. A category presented an odds ratio of 7.14 (0.012) for unsatisfactory bulls. A low percentage of the C category (2.3%) was observed in both BSE classifications. Vacuoles or craters were predominantly observed in the post-acrosomal and mid-subacrosomal regions, with minimal occurrence in the apical ridge region. Our findings provide the baseline for nuclear defects in B. indicus and its crossbreeds. The Feulgen reaction thus enables a simple yet comprehensive analysis of nuclear sperm head defects during BSE. In addition, stain retention facilitates a practical evaluation and an accurate account of the nuclear lesion types.