Abstract
Summary. With Rikmenspoel's photo-electric method, the initial mean velocity and number of normally moving bull spermatozoa per unit volume, the velocity frequency distributions and the rates of decrease of numbers and velocity with time have been studied, using a standard egg-yolk-citrate diluent at pH 6·75 (= 6·80 at 37° C). The distribution of mean velocities between ejaculates differs significantly from a Gaussian one, but conforms within measuring error with a logarithmic distribution. No significant differences in initial velocity of the spermatozoa between bulls were found on random sampling with respect to feeding and keeping conditions and season. A positive correlation was found between the number of normally moving spermatozoa Nmov per unit volume and the total sperm concentration (r = +0·43), and a negative correlation between Nmov and the mean velocity [unk] (r = -0·54). There was no correlation between the mean velocity and total sperm concentration (r = 0·06). Ageing was studied on storage for 20 hr or longer in a Dewar vessel with ice. The velocity decrease with time -∂[unk]/∂t was 0·66±0·39 (μ/sec)/hr (s.e. = ±0·06), mode 0·30 (μ/sec)/hr, and the half-life period of the number of normally moving spermatozoa t½(N) was 60 ±44 (s.d.) (s.e. = ±7·6) with a mode of 30 hr. Significant correlations were found between -∂[unk]/∂t and the initial mean velocity [unk]0 (r = +0·57) and between log (-∂[unk]/∂t) and log t½(N) (r = -0·40). There was no correlation between the initial number of normally moving spermatozoa N0 per unit volume and t½(N) (r =0·114; 0·50<P<0·60). It is concluded that although high initial swimming velocity of bull spermatozoa might still be thought to be advantageous for fertilization in natural mating, this will probably not be so when the semen is used for artificial insemination, since the higher the initial velocity is, the shorter the period during which it is maintained and the shorter the period of survival of normally moving spermatozoa. It appears that the rates of velocity-decrease with time, and the half-life period of the number of spermatozoa moving normally, are more important for evaluating the quality of semen samples with respect to motility characteristics than the initial swimming velocity of the spermatozoa.
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