Sperm morphology assessment is a critical determinant of fertility in livestock. However, anecdotal reports suggest the accuracy of sperm morphological classification varies considerably between assessors. This research aimed to (1) characterise the variation in sperm morphology classification between morphologists using both simple (two category) and complex (30 category) classification systems, and (2) characterise the variation between two types of microscope optics (phase contrast and differential interference contrast; DIC).
Images of individual ram sperm (n = 800/optic, 400x magnification) were labelled using up to 30 morphology categories by four experienced sperm morphologists, this labelling was then simplified to a normal/abnormal categorisation for comparison.
When using the normal/abnormal classification system with DIC, morphologists agreed on the label of 585 sperm out of 800 and when labelling with the 30-category system the morphologists agreed on 212 sperm out of 800. When using the normal/abnormal classification system with phase contrast the morphologists agreed on the label of 641 sperm out of 800 and when labelling with the 30-category system the morphologists agreed on 253 sperm out of 800.
In conclusion, sperm that were captured using phase contrast optics led to a higher degree of consensus amongst morphologists when compared to DIC. The variation decreased for both optics as the complexity of the labelling system increased. Further investigation into how standardisation may influence these results would be interesting to understand how this variation could be minimised.