Three semen ejaculates were collected weekly for eight successive weeks
from three mature buffalo bulls to study the effect of melatonin on storability of buffalo
bull semen. Only ejaculates with 70% of spermatozoa exhibiting progressive motility
were included in the present study. The semen was extended by using Tris-egg yolk
diluent to obtain 100 x 10⁶ sperm J'er ml. Melatonin was added tc diluted semen as
0.0, 10, 20 and 30 J,lg/100 x 10 sperm. Thereafter, diluted semen (control and
treatments) was split into tow portions. The first part was stored at refrigerator (4°C)
temperature for five days and examined daily for motility, live sperm percentage,
sperm abnormality % as well as GOT, GPT release and fructose content in seminal
plasma. The second portion was frozen in 0.25 ml straws after 4 h equilibration period
at 5°C post dilution. Straws were stored in liquid nitrogen for 24 h before thawing in
water bath at 37°C for 30 sec. The results showed that the addition of 10 J,lg or 20 J,lg melatonin improved
(P < 0.05) sperm motility, live sperm % and reduced percentage of sperm abnormality
for 5 days of storage (at 4°C). The release of both GOT and GPT from spermatozoa
into seminal plasma was significantly (P < 0.05) minimized in the presence of 20 J,lg
melatonin compared with other treatments. Concerning fructose content in seminal
plasma, addition of melatonin had a significant (P < 0.05) effect on conservation of
energy in seminal plasma. The enzyme activities released to the seminal plasma
were negatively correlated with sperm motility and positively correlated with sperm
abnormality. The presence of 20 J,lg melatonin in the extender resulted in higher (P <
0.05) frozen-thawed motility compared to other treatments. It is concluded that buffalo
semen could be successfully preserved for 5 days by addition of melatonin in Tris-
extender at 4°C.or - 196°c