New aspects of boar semen freezing strategies

fAlthough cryopreserved boar semen has been available since 1975. a major breakthrough in commercial application has not yet occurred. There is ongoing research to improve sperm survival after thawing, to limit the damage occuring to spermatozoa during freezing and 10 further minimize the number of spermatozoa needed to establish a pregnancy. Boar spermatozoa are exposed to lipid peroxidation during freezing and thawing, which causes damage to the sperm membranes and impairs energy metabolism. The addition of antioxidants or chelating agents (e.g. catalase, vitamine E, glutathione, butylated hydrotoluene or superoxide dismutase) to the still standard egg-yolk based cooling and freezing media for boar semen, effectively prevented this damage. In general, final glycerol concentrations of 2-3% in the freezing media, cooling rates of -30 to -50 degrees C/min, and thawing rates individually optimized for sub-standard 1200-1800 C/min resulted in the best sperm survival. However. cooling, and thawing rates individually optimzied for sub-standard freezing boars have substantially improved their sperm quality after cryopreservation. With deep intrauterine insemination, the sperm close has been decreased front 6 to I x 109 spermatozoa without compromising farrowing rate or litter size. Minimizing insemination-to-ovulation intervals. based either on estimated or determined ovulation. have also improved the fertility after Al with cryopreserved boar semen. With this combination of different approaches, acceptable fertility with cryopreserved boar semen can be achieved, facilitating the use of cryoprcserved boar semen in routine Al programs. (C) 2008 Elsevier Inc. All rights reserved