A total of 5186 ejaculates from 115 boars of five breeds (48 Yorkshire, 25 Landrace, 20 Duroc, 18 Hampshire and four Lacombe) were collected and frozen between 1975 and 1980. Frozen semen was thawed and evaluated for percentage progressive motile sperm (post-thaw rating) and loss in percentage motile sperm due to freezing and thawing. Boar repeatabilities and effects of breed of boar, year, month, age of boar at collection and percentage of extender added were examined. Boar repeatabilities were 0.32 for post-thaw rating and 0.22 for loss in percentage motile sperm. Breed of boar was not significant. Year was significant, and percentage motile sperm recovered declined from 1976 through 1980. Semen collected between March and May had the highest post-thaw rating. As age of boar increased, post-thaw rating declined and loss in percentage motile sperm increased. As the percentage of extender added to semen increased, so did the loss in percentage motile sperm after freezing. Correlations between post-thaw rating and fresh semen motility score, volume, concentration and percentage motile sperm were 0.24, 0.03, −0.20 and 0.25, respectively. Respective correlations of fresh semen measures with loss in percentage motile sperm after freezing were 0.15, 0.01, 0.17 and 0.23. The current practice of standardizing fresh semen to a given concentration before freezing does not result in a standard frozen-thawed product with respect to percentage motile sperm.
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Joyal et al. (1986) studied this question.
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