STUDIES ON DOG SEMEN

Semen was collected by artificial vagina from three adult dogs of mixed breed twice weekly during the 1st year, once weekly during the 2nd year, and twice monthly during the 3rd year. Ejaculates were collected entire, or in separate fractions—the first or pre-sperm, the second or sperm-rich, and the third or post-sperm fractions. The average total duration of ejaculation was 11 min, the greater part of this time, 8 min, consisting of ejaculation of the third fraction. The average total ejaculate volume was 12·0 ml, the values for the first, second, and third fractions being 0·9, 2·6, and 9·2 ml, respectively. The average sperm concentration of the total ejaculate was 53 × 106cells per ml, the values for the second and third fractions being 247 × 106and 10 × 106cells per ml, respectively. In nigrosin-eosin stained preparations, the average percentage of 'dead' (eosin-stained) spermatozoa per ejaculate at room temperature varied from fifteen in second-fraction samples to twenty in total-ejaculate samples. The dimensions of normal unstained spermatozoa in these preparations were: total length 68 μ, head length 7 μ, head width 5 μ, midpiece length 11 μ, and tail length 50 μ. The average percentage of abnormal spermatozoa per ejaculate was fifteen. The head and tail regions of spermatozoa were affected by the highest percentage of abnormalities. Alteration in semen quality with seasonal variation or change in collection frequency was only significant (P<0·01) for the total ejaculate volume of individual dogs. Dog spermatozoa retained their motility for a greater length of time in phosphate buffered sperm suspensions than in undiluted semen, and motility was adversely affected at body temperature. The longest preservation of progressive motility at room temperature, 32 hr, was associated with the spermatozoa in a second-fraction semen sample diluted with egg-yolk citrate.