Bull sperm morphology assessment varied by evaluator

Abstract

Assessment of sperm morphology is an important part of bull breeding soundness evaluation (BBSE). Whereas the effects of
evaluator experience and evaluation method on the sperm morphology estimation were assessed in other species, no such study
was conducted for bulls. Our objectives were to assess the effects of evaluator experience and number of sperm assessed on BBSE
outcomes. A single eosin-nigrosin sperm morphology slide from individual semen samples, collected from 35 yearling bulls
was used. In Experiment I, 6 individuals (3 board-certified theriogenologists [DACT] and 3 fourth-year veterinary students [VS])
evaluated 100 sperm from 35 slides twice (at least 1 week between evaluations). In Experiment 2, 3 DACT evaluated 100, 200,
and 400 sperm from the same 5 sperm morphology slides to determine if assessing a higher number of sperm would increase the
agreement of morphologic characteristics. In Experiment 1, there was a difference (p < 0.0001) in the percent of sperm classified
as morphologically normal between evaluator types (VS versus DACT). Furthermore, variation among evaluators affected sperm
morphology assessments and bull breeding soundness evaluation classifications. Whereas the time needed to evaluate slides increased
(p = 0.96) with increasing number of sperm assessed, there was no effect (Experiment 2) of number of sperm evaluated
on percent normal sperm, indicating that evaluating more than 100 sperm may not be justifiable. Further investigation on slide
preparation, microscope use, assessor experience, and continuing education/training is important to ensure the repeatability and
validity of evaluating bovine sperm morphology.