In the top of the selective breeding pyramid, frozen/thawed semen
can be useful. However, although various authors have reported
fertility levels of Æ90% with frozen/thawed poultry semen [19–
22], the possibility of using frozen semen seems underestimated in
the poultry industry. Currently, cryopreservation of avian semen
does play a role in ex situ gene banking to preserve endangered wild
species or for preserving genetic diversity in commercial species
(Reviewed in [9]). Main repositories are those of the North American USDA National Animal Germplasm Program [23], the French
National Cryobank of Domestic Animals [24], and the Dutch
Centre for Genetic Resources, the Netherlands (CGN) [21]. Additionally, many other countries have germplasm repositories of
domestic bird species in private companies or public research institutes. In addition to (longer-term) gene banking of endangered
breeds, frozen semen can also be important for maintaining breeding lines in research institutes and poultry breeding organizations,
as a cost-effective strategy compared with holding and propagating
live birds.
1.3 Extenders
and Freezing Media
Both for freezing semen and for the fresh use of semen, the diluent
medium used is very important. The dilution of semen provides the
sperm cells space and access to oxygen and substrates for metabolism. Access to oxygen or to a glycolyzable substrate (depending on
the species) is important during semen storage [25–27]. Also a
stronger dilution makes that the milieu for the sperm cells does
not rapidly deteriorate as a result of products of cell metabolism. In
our experience, a strong dilution is favorable for the survival of
sperm cells during cold storage, provided that a suitable diluent
with a physiological osmolality is used. With a modified (see below)
version of a diluent described in [28], motility was maintained at
virtually “unlimited” (>10
6 times) dilution (Woelders, not published). Sexton [29] reported a negative effect of semen dilution,
although Blesbois and de Reviers [30] explained how in fact specific
fractions of seminal plasma were responsible for the declined fertility in diluted semen. A positive effect of dilution of chicken semen
was reported by Parker and McDaniel [31]. The latter authors also
showed how the effect of dilution depends strongly on the type of
diluent used, with negative effects of diluting with seminal plasma
and positive effects of diluting (up to 200-fold dilution rate) with
culture medium MEM. For insemination of chickens with “fresh”
semen, one could easily dilute the semen 40 times to provide a
sufficient (see [19]) sperm dosage in an acceptable insemination
volume. We would advise to use a dilution rate of >10 times if
cold storage, e.g., during 24 h or 48 h, is required. It has been
clearly demonstrated that good fertility can be obtained with stored
poultry and turkey semen [25–28]. Also for freezing of avian
semen, higher dilution rates appear beneficial [22], and we have
Cryopreservation of Avian Semen
381
can be useful. However, although various authors have reported
fertility levels of Æ90% with frozen/thawed poultry semen [19–
22], the possibility of using frozen semen seems underestimated in
the poultry industry. Currently, cryopreservation of avian semen
does play a role in ex situ gene banking to preserve endangered wild
species or for preserving genetic diversity in commercial species
(Reviewed in [9]). Main repositories are those of the North American USDA National Animal Germplasm Program [23], the French
National Cryobank of Domestic Animals [24], and the Dutch
Centre for Genetic Resources, the Netherlands (CGN) [21]. Additionally, many other countries have germplasm repositories of
domestic bird species in private companies or public research institutes. In addition to (longer-term) gene banking of endangered
breeds, frozen semen can also be important for maintaining breeding lines in research institutes and poultry breeding organizations,
as a cost-effective strategy compared with holding and propagating
live birds.
1.3 Extenders
and Freezing Media
Both for freezing semen and for the fresh use of semen, the diluent
medium used is very important. The dilution of semen provides the
sperm cells space and access to oxygen and substrates for metabolism. Access to oxygen or to a glycolyzable substrate (depending on
the species) is important during semen storage [25–27]. Also a
stronger dilution makes that the milieu for the sperm cells does
not rapidly deteriorate as a result of products of cell metabolism. In
our experience, a strong dilution is favorable for the survival of
sperm cells during cold storage, provided that a suitable diluent
with a physiological osmolality is used. With a modified (see below)
version of a diluent described in [28], motility was maintained at
virtually “unlimited” (>10
6 times) dilution (Woelders, not published). Sexton [29] reported a negative effect of semen dilution,
although Blesbois and de Reviers [30] explained how in fact specific
fractions of seminal plasma were responsible for the declined fertility in diluted semen. A positive effect of dilution of chicken semen
was reported by Parker and McDaniel [31]. The latter authors also
showed how the effect of dilution depends strongly on the type of
diluent used, with negative effects of diluting with seminal plasma
and positive effects of diluting (up to 200-fold dilution rate) with
culture medium MEM. For insemination of chickens with “fresh”
semen, one could easily dilute the semen 40 times to provide a
sufficient (see [19]) sperm dosage in an acceptable insemination
volume. We would advise to use a dilution rate of >10 times if
cold storage, e.g., during 24 h or 48 h, is required. It has been
clearly demonstrated that good fertility can be obtained with stored
poultry and turkey semen [25–28]. Also for freezing of avian
semen, higher dilution rates appear beneficial [22], and we have
Cryopreservation of Avian Semen
381