Data of spermatological traits of 3490 ejaculates obtained during four years (1987 to 1990) from ten Friesian bulls were investigated to see the effects of age, seasons and bulls upon different seminal attributes. The age-wise overall mean values of different attributes of these bulls were: age and body weight at first ejaculation 329.7 days and 337.1 kilograms, number of ejaculates 7.41, ejaculate volume 4.08 ml, mass motility 1.14 grades, initial motility 51.43 per cent, sperm cells concentration 601.09 millions per ml, discarded ejaculates 3.17 and doses produced per ejaculate 32.66 number.

Age exerted highly significant effect (P<0.01) upon number of ejaculates, ejaculate volume, sperm concentration, ejaculate discarded and doses per ejaculate. A significant effect (P<0.05) was observed on percentage motility. There was a non-significant effect on moss motility. The 4th year was proved to be the best age for semen production because mean values of three seminal characteristics namely number of ejaculates, ejaculate volume and percentage motility were maximum during this year. Minimum mean ejaculates were also discarded during the 4th year.

Second year was observed as the worst year for semen production. Minimum mean values of number of ejaculates, ejaculate volume and percentage motility were observed in this year. Maximum mean ejaculates were also discarded during second year of age.

Seasons exerted highly significant effect (P<0.01) upon mass motility, percentage motility, sperm concentration, discarded ejaculates and doses per ejaculate. A significant effect (P<0.05) of seasons was observed upon number of ejaculates but the effect on ejaculate volume was non-significant (P>0 05)

The winter was proved to be the best semen producing season, because two seminal characteristics i.e. mass motility and pci centage motility had maximum mean values in this season Minimum mean ejaculates were also discarded in winter season The second best season was spring, in which ejaculate volume and doses per ejaculate were at their highest mean values

The worst season for semen production was humid hot season. Four seminal attributes i.e. number of ejaculates, mass motility, percentage motility and sperm concentration had minimum mean values in this season. Maximum mean ejaculates were also discarded in humid hot season. The second worst season was autumn. Only mean ejaculate volume and doses per ejaculate were at their lowest margin in autumn.

Highly significant effect (P<0.01) of bulls was observed upon ejaculate volume, mass motility and sperm concentration. Significant effect (P<0.05) of bulls was recorded for initial percentage motility and semen doses per ejaculate. The effect of bulls upon number of ejaculates and ejaculates discarded was found to be non-significant (P>0.05).

Bull No. F 16 proved to be the best bull for semen quantity and quality withmaximum number of ejaculates and maximum ejaculate volume. F 16 was also good in percentage motility, sperm cell concentration and doses per ejaculate. Moreover minimum ejaculates were discarded of F 16 too.

Bull No. 10 was the worst bull. Lowest values were observed in number of ejaculates, percentage motility and sperm concentration. F 10 was also not good in mass motility and maximum ejaculates were discarded from this bull.

The principle conclusion of this study is that if appropriate steps are taken to mitigate the effects of climate and high level of management practices is maintained, there appears to be no reason why high ambient temperatures and humidities should be inimical to successful semen production with Friesian bulls in the subtropical environments