Prevalence of spermatozoa morphologic defects from Zebu bulls under free mating system

Abstract

Bulls are keys to fertility and genetic improvement of the total herd. Spermatozoa quality is among of major components for evaluation of bulls to be used as breeding bulls. This study was therefore carried out to determine the prevalence of spermatozoa defects in Tanzania shorthorn breeding bulls, and to determine if the defects vary with scrotal circumference (SC), age and testicular pathology. Age was determined by dentition and SC measured by using standard scrotal metal. Sperm cells were collected by epididymal aspiration procedure and stained with Carbol-fuchsin. One hundred spermatozoa were counted per slide and each classified into normal or abnormal. Three testicular samples were taken after slaughter and processed for histological examination by staining with hemotoxylin and eosin. Forty sections of seminiferous tubules per section were evaluated and classified into either normal or abnormal. After examinations, 169 and 134 bulls were classified as satisfactory (normal) and unsatisfactory (abnormal) breeders, respectively. The mean SC (in centimeters) and percentages spermatozoa defects in normal and abnormal bulls were 28.9±2.6 and 15.6±2.5 versus 22.0±3.6 and 39.0±9.1, respectively. Most frequently observed primary spermatozoa defects in normal bulls were Stump-tail, DAG defect and decapitated sperm head while the secondary spermatozoa defects were loose head, bent tail, and proximal and distal cytoplasmic droplets. Bulls with severe testicular lesions had high percentages of spermatozoa defects which increased with severity of testicular abnormalities (P < 0.01). The results confirm the absence of proper criteria for selecting breeding bulls and support the earlier evidence of association between SC, testicular pathology and spermatozoa defects in bulls.

Key words: Tanzania shorthorn zebu bull, spermatozoa defects, scrotal circumference, testicular pathology,