Aim: To study whether additional measurements of motility characteristics of spermatozoa by computer assisted semen analysis (CASA) were more sensitive indicators of reduced semen quality than estimates of percentages of motile, rapid or progressive cells.

Methods: Intermittent scrotal insulation was applied to 6 rams for 16 h per day for 21 days or to 2 of these for 12 h per day for 28 days in the following year. Semen was collected and evaluated by CASA immediately and either frozen or stored at 30°C or 5°C before re-evaluation.

Results: Intermittent scrotal insulation caused falls in the percentage of motile, progressive and rapid sperm, as did freezing-thawing and storage at 30°C or 5°C. Motility characteristics (amplitude of lateral head displacement, mean path velocity, mean progressive velocity and curvilinear velocity), as determined by CASA fell only when the percentage of motile sperm was already reduced. Freezing and thawing or liquid storage of the semen from insulated rams caused a greater fall in the percentage of motile and rapid sperm than control semen, but only affected the motility characteristics when the percentage of motile sperm was already reduced.

Conclusion: Intermittent scrotal insulation affected not only the motility of the freshly collected sperm, but also their ability to withstand the additional stress of storage. The additional data on motility characteristics obtained by CASA appeared to be no more a sensitive indicator than the percentage of motile cells of reductions in semen quality.

Keywords: testis, scrotal insulation, semen evaluation

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