The effect of straw size, freezing rate and thawing rate upon post-thaw quality of dog semen

Abstract

Optimal freeze–thaw processes for dog semen will yield a maximal number of insemination doses from an ejaculate. The objectives of this study were to compare the effects of two straw sizes (0.25- and 0.5-mL French), two freezing rates (straws suspended 3.5 and 8 cm above liquid nitrogen) and two thawing rates (in water at 37 and 70 °C) upon post-thaw quality of dog semen, and to determine the best treatment combination. Quality was expressed in terms of the percentage progressively motile sperm 5 and 60 min after thawing and the percentage of abnormal acrosomes 5 min after thawing. One ejaculate from each of eight dogs was frozen. Two straws from each ejaculate were exposed to each of the eight treatment combinations. Data were analyzed by means of a repeated measures factorial analysis of variance and means compared using Bonferroni's test. Dog affected each response variable ( P < 0.01). Neither straw size, nor freezing rate, nor thawing rate affected motility 5 min after thawing ( P > 0.05). Half-milliliter straws resulted in 5.7% more progressively motile sperm 60 min after thawing and 6.5% fewer abnormal acrosomes than 0.25-mL straws ( P < 0.05, n = 64). The percentage progressively motile sperm 60 min after thawing tended to be higher for semen thawed at 70 °C compared to 37 °C ( P < 0.06, n = 64). Semen thawed in water at 70 °C had 6.6% fewer abnormal acrosomes than semen thawed in water at 37 °C ( P < 0.05, n = 64). Freezing rate interacted with thawing rate ( P < 0.05) in their effects upon acrosomal morphology and freezing 8 cm above liquid nitrogen and thawing in water at 70 °C was best. Dog semen should be frozen in 0.5-mL straws, 8 cm above liquid nitrogen and thawed in water at 70 °C.