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Summary Furty‐seven A. I. bulls between 15 and 26 months of age, were used to study the relationship between sperm morphology in fresh semen and fertility (56‐day non‐return rate) in frozen semen following 11,749 inseminations. The sperm morphology was studied in two freezing operations/bull in a phase‐contrast microscope and morphological abnormalities were recorded as a percentage of the total number of counted spermatozoa. Morphological categories used in this study were abnormal heads, detached heads, nuclear pouches, abnormal acrosomes, proximal cytoplasmic droplets, abnormal midpieces and abnormal tails. The greatest mean value recorded for the investigated categories was found for abnormal heads (3.8%) but the majority of morphological abnormalities only occurred in about 1 % of all studied spermatozoa. Breed effects were found, with a somewhat higher incidence (p ≤ 0.05‐0.01) of sperm abnormalities and poorer fertility among SRB than among SLB bulls. Despite the low frequency of sperm abnormalities, statistically significant (p ≤ 0.05‐0.001) correlations were found between abnormal heads, nuclear pouches and proximal cytoplasmic droplets assessed in fresh semen and fertility (56‐day non‐return rate) of frozen semen.

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