Liquid preservation ensures a storage time of approximately 3–5 d, with a maximum of 7 d. From these, 99% are preserved in a liquid form. Weitze estimated that 155 × 10 6 sperm dosages are produced for artificial insemination annually worldwide. Consequently, successful viability of frozen–thawed boar spermatozoa was reported, ,, ,, ,. Fertility reports with deep frozen bull spermatozoa led to intensive development of cryopreservation methods that would be applicable for practical insemination purposes, including research to develop a method for deep freezing boar semen.
He opened up an era of successful cryopreservation methods, not only of gametes from various species, but also of other somatic cells and tissues. These two reports rank as the earliest in the recovery of mammalian cells after exposure to a temperature below their freezing point.Īt least as important was the discovery of the cryoprotective potential of glycerol by Polge et al. A century later, Mantegazza observed that human spermatozoa survived when semen was frozen at −17 ☌. When he re-warmed them after 30 min, they became motile again. Īs early as 1776, Spallanzani observed sperm immobilization by cooling/freezing when he exposed spermatozoa from humans, stallions and frogs to snow. Although new trends, including microinjection of dry frozen or dry fixed spermatozoa, or culture and transplantation of spermatogonial stem cells are subjects of intensive research, liquid preservation and cryopreservation of spermatozoa are the current choices for storage and commercial use of porcine semen. Despite its utilization in some commercial production applications, for example in genetic transfer projects, frozen boar semen has not been used under production conditions as efficiently as liquid-preserved semen, due to the high susceptibility of boar spermatozoa to damage during cryopreservation and a complicated process of deep freezing. With this combination of different approaches, acceptable fertility with cryopreserved boar semen can be achieved, facilitating the use of cryopreserved boar semen in routine AI programs.Ĭryopreserved boar sperm has been available for commercial use since 1975. Minimizing insemination-to-ovulation intervals, based either on estimated or determined ovulation, have also improved the fertility after AI with cryopreserved boar semen.
With deep intrauterine insemination, the sperm dose has been decreased from 6 to 1 × 10 9 spermatozoa without compromising farrowing rate or litter size. However, cooling and thawing rates individually optimized for sub-standard freezing boars have substantially improved their sperm quality after cryopreservation. In general, final glycerol concentrations of 2–3% in the freezing media, cooling rates of −30 to −50 ☌/min, and thawing rates of 1200–1800 ☌/min resulted in the best sperm survival. catalase, vitamin E, glutathione, butylated hydroxytoluene or superoxide dismutase) to the still standard egg-yolk based cooling and freezing media for boar semen, effectively prevented this damage. The addition of antioxidants or chelating agents (e.g. Boar spermatozoa are exposed to lipid peroxidation during freezing and thawing, which causes damage to the sperm membranes and impairs energy metabolism. There is ongoing research to improve sperm survival after thawing, to limit the damage occurring to spermatozoa during freezing, and to further minimize the number of spermatozoa needed to establish a pregnancy. Although cryopreserved boar semen has been available since 1975, a major breakthrough in commercial application has not yet occurred.
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