Predicting reproductive outcome from sperm measurements in Swiss (CD-1) mice

Recent advances in the quantification of sperm characteristics, particularly by techniques of videomicrography, raise the problem of identifying a subset of sperm measurements that can accurately predict reduced reproductive performance in the presence of a reproductive toxicant. This paper discusses and illustrates, with sperm data from Swiss (CD-1) mice, three properties of sperm measurements in addition to the association with reproductive outcome that can be used as objective criteria to distinguish among potentially useful sperm characteristics. Identification of these properties was motivated by the need to single out sperm characteristics that would yield hypothesis tests with good power to distinguish groups with altered sperm characteristics from those with normal sperm characteristics. The list of desirable properties of sperm characteristics includes: a)

The most useful sperm characteristics will exhibit low measurement bias and high measurement precision. b) Distribution: Sperm characteristics that follow the class of normal distributions allow easy identification of the most powerful hypothesis testing procedures. c) Variation: Sperm characteristics that exhibit limited variation from individual to individual will make altered values easier to detect. d) Correlation: Sperm characteristics that exhibit a high correlation with reproductive outcome will be most useful. MEASUREMENTs of sperm concentration, sperm motility, and abnormal sperm were examined for each of these properties in Swiss (CD-1) mice. For control animals, evidence of measurement bias between labs and significant variation among studies within labs was found for each sperm characteristic, with measurements of abnormal sperm exhibiting the least bias. Sperm concentration and the natural logarithm of abnormal sperm appeared normally distributed. Individual to individual variation was substantial for sperm motility and sperm concentration, both of which required an approximately 30% decrease in mean to achieve good statistical power. In contrast, abnormal sperm required only a 4% increase in mean to achieve the same power. In spite of the measurement noise associated with these sperm characteristics, data from 25 experiments indicated good agreement between the results of hypothesis tests based on sperm characteristics and reproductive outcome as judged by fertility and the number of pups. The same conclusions reached for reproductive outcome were reached in 19 of 24 experiments for sperm motility, in 19 of 25 experiments for sperm concentration, and in 17 of 24 experiments for abnormal sperm.