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Total Sperm per Ejaculate of Men: Obtaining a Meaningful Value or a Mean Value With Appropriate Precision

PHILLIP L. CHAPMAN

From the ^* Animal Reproduction and Biotechnology Laboratory and the Department of Statistics, Colorado State University, Fort Collins, Colorado.

Correspondence to: Dr Rupert P. Amann, 909 Centre Ave, #123, Ft Collins, CO 80526-2091 (e-mail: rpalra62{at}comcast.net).

Abstract

We retrospectively mined and modeled data to answer 3 questions. 1) Relative to an estimate based on 20 semen samples, how imprecise is an estimate of an individual's total sperm per ejaculate (TSperm) based on 1 sample? 2) What is the impact of abstinence interval on TSperm and TSperm/h? 3) How many samples are needed to provide a meaningful estimate of an individual's mean TSperm or TSperm/h? Data were for 18–20 consecutive masturbation samples from each of 48 semen donors. Modeling exploited the gamma distribution of values for TSperm and a unique approach to project to future samples. Answers: 1) Within-individual coefficients of variation were similar for TSperm or TSperm/h abstinence and ranged from 17% to 51%; average 34%. TSperm or TSperm/h in any individual sample from a given donor was between –20% and +20% of the mean value in 48% of 18–20 samples per individual. 2) For a majority of individuals, TSperm increased in a nearly linear manner through 72 hours of abstinence. TSperm and TSperm/h after 18–36 hours' abstinence are high. To obtain meaningful values for diagnostic purposes and maximize distinction of individuals with relatively low or high sperm production, the requested abstinence should be 42–54 hours with an upper limit of 64 hours. For individuals producing few sperm, 7 days or more of abstinence might be appropriate to obtain sperm for insemination. 3) At least 3 samples from a hypothetical future subject are recommended for most applications. Assuming 60 hours' abstinence, 80% confidence limits for TSperm/h for 1, 3, or 6 samples would be 70%–163%, 80%–130%, or 85%–120% of the mean for observed values. In only 50% of cases would TSperm/h for a single sample be within –16% and +30% of the true mean value for that subject. Conclusions: Pooling values for TSperm in samples obtained after 18–36 or 72–168 hours' abstinence with values for TSperm obtained after 42–64 hours is inappropriate. Reliance on TSperm for a single sample per subject is unwise.

     Key words: Imprecision of total sperm per ejaculate, abstinence interval, meaningful semen data, noninvasive evaluation of spermatogenesis

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