Sperm morphology is subjectively assessed using a phase contrast microscope and scored simply as normal or abnormal. Visual assessment allows identification of abnormalities to the sperm head, acrosome, midpiece or tail which may contribute to abnormal motility or reflect incomplete sperm maturation. Furthermore, abnormalities in sperm morphology are associated with male fertility issues leading to reduced conception rates. Morphology assessments are paramount in breeding programs to ensure that sires are producing normal sperm which will maximise reproductive success. 


Most guidelines deem a bull semen sample to have acceptable sperm morphology if less than 30% abnormal spermatozoa are detected. For frozen-thawed sheep semen, less than 15% abnormal spermatozoa is usually considered the acceptable threshold.

Examples of abnormalities which may be detected during morphological assessment are represented in the graphic below.