Proper integration of PAWP in the sperm head structures appears to be reflective of bulls' sperm quality and of sperm head morphology in particular. Defective spermatozoa displayed various anomalies of PAWP labeling and often show the presence of ubiquitin on their surface (Fig. 1).41 Consequently, correlations are being explored between flow cytometric PAWP levels and the parameters of bull sperm quality and fertility.