摘要
Artificial insemination made a predominant contribution towards the improvement of genetic potential and increased productivity in animal husbandry sectors. In frozen semen technology, about 50% of sperm died because of cryoinjury or cryodamage during the process of cryopreservation and thawing of the semen. These cryo-damages can be minimized by use of various cryoprotective agents or cold shock absorbers in the frozen semen technology. Of which, egg yolk (EY) is most primarily important in the extender preparation for various mammalian species for longer period and it works against the cold shock during the cryopreservation process due to the presence of low density lipoproteins (LDL). Further, EY contains substances other than LDL that affect the sperm quality parameters especially reduced motility and inhibit the respiration of sperm;therefore, there was heavy demand on replacement of the EY with the particular responsible substances (LDL) in the semen extender. Later on, various investigators tried to extract the LDL from the EY of hen and finally succeeded to extract the LDL from the EY of hen for semen preservation of various species. The concentration of LDL used in various species is varied and this may be due to the composition and concentration of phospholipids, cholesterol and its proportion in the sperm membrane. In bovine species, the concentration of LDL was standardized as 8% (w/v) on dry matter basis. This is equal to 20% EY used in conventional semen extender. As it is explained that the 20% EY contains 68% LDL (13.6 g) and on dry matter basis, it is approximately 60% (8.16 g). This calculation indicates 20% EY contains 8% LDL on dry matter basis. The LDL protects the sperm by various mechanisms to maintain the integrity of sperm membrane, which is explained in the present review. It was concluded that the investigation is still to be carried out to find out the exact roles of apoproteins and lipids of LDL and to indentify and isolate the detrimental substances presented in the whole EY.
