Sheep - AgRIS

6. Nutrients
Although spermatozoa utilize fructose and glucose in order of priority but maltose,
raffinose, lactose, trebalose have given better results in freezing experiments.
7. Antibacterial agents
Bacteria are practically omnipresent. Spermatozoa like the living cells, have to be kept
away from bacteria and be controlled by providing suitable bactericides antibiotics.
8. Dilution rate
It includes the number of live normal spermatozoa to be in- cluded per ml of the diluted
semen per insemination dose while freezing in straws. Normally ram semen contains 3000-
5000 million sperms per ml of the neat semen and only 100-150 million sperms are enough to
impregnate an ewteven though only one spermatozoa takes part in fertilization process. In
certain extenders used for freezing, dilution rates of 1:2 and 1:3 have given better results than
dilution rate of 1:1 which is general practice for short term preservation or for imrnediate use.
9. Rate of heat exchange
It is the most important factor which needs monitoring. It is important not only to control
the rate of echange of heat at the time of cooling but also at the time of thawing revival. It is
clarified by some workers that it should be equal in both the stages and certain workers prefer
high rate of cooling as well as thawing i.e. using high temperature water bath. There is a critical
zone oftemperature which is particularly harmful for the spermatozoa and the latter group in the
absence of the knowledge of that zone advise the practice of fast rate of heat exchange. Now a
days computer controlled programmable cooling and thawing cabinets are available and the day
is not for offwhen the critical temperature zone will be identified and the measures to pass
through it will be devised for successfully freezing the ram semen. Some workers have advised
thawing the pelleted frozen semen in media like citrate solution others however, have found no
difference between the results of thawing with or without the medium. Some prefer freezing
pellets while the others prefer freezing in straws to give wider surface area for quicker heat
exchange. Pellets are prepared by dropping 0.2 ml of diluted equilibrated semen in the smooth
pits carved on the surface of plas tic tray floating on liquid nitrogen allowing it to freeze for 3-5
minutes, collecting the pellets into the goblets and lowering down into the liquid nitrogen for
storage. Allowing the liquid nitrogen in direct contact or not has made no difference. Straws
have to be filled in the clean cabinet atomosphere of 4-5°C temperature after equilibration,
sealed, exposed to certain temperature below 0°C for a particular length of time and then only
lowered into liquied nitrogen (-196°C) for storage. These days small size liquid nitrogen
containers are also available for transporting smaller quantities of frozen semen. During
thawing certain workers have claimed good results with as low temperature of water bath as
37°C, while some advise as high as 75°C. Similarly the time for exposure may be 10-15
seconds for straws while 1-2 minutes for pellets.
10. Additives
Addition to the semen of certain chemicals like cortisol, amylase, glucoronidase which
play part in longivity of the spermatozoa in the female reproductive tract and are reported to be
deficit under stressful conditions in the tract and their varying concentration in the ram semen
with season, individuality etc, chelating agents like EDTA are also under study to see their
effects vis-a-vis fertility rate.
The process of freezing adversely affects the survival of sper matozoa. It is dependent
upon number of inter-related factors such as diluent composition, concentration of
cryoprotectant, dilution rate, size of pellet or straw and rate of freezing or thawing.
There are some problems in achieving desirable lambing rate with the use of frozen
semen. Unlike other species, the complex anatomy of the ewe‘s cervix does not permit
smooth passage for frozen thawed spermatozoa in the cervical canal. Concerted efforts
are going on to improve the fertility of frozen semen by improving the procedures of
ram semen freezing and to develop better insemination techniques for laparoscope
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