1.2 Background
Cryopreservation protocols for semen are described in the literature for a number of bird species used in animal production, as well
as for fancy and other hobby species and wild bird species.
In birds and other macrolecithal taxa, cryopreservation of the
ova or embryos is not possible. If only male gametes (i.e., semen)
can be used, it would take at least six generations of backcrossing
with frozen-thawed semen to recover a lost endangered breed or a
selection line. This makes it laborious and costly, and it is therefore
less practical. Collection, cryopreservation, and use (grafting) of
avian ovaries [5, 6] or primordial germ cells [7, 8] are potential
alternative strategies that are currently being developed. This chapter will only discuss methods for cryopreserving avian semen.
Most studies on freezing of avian semen have been done with
domestic bird species. Semen cryopreservation is described for
other domestic bird species, including turkey, duck species, goose,
and guinea fowl [9]. More recent studies or reviews have been
published, e.g., for quail [10], emu [11], guinea fowl [12, 13],
and goose [14]. Cryopreservation of nondomestic bird species was
reviewed in [15, 16]. More recent studies are, for example, for
crane species (e.g., [17]) and pigeon (e.g., [18]).
Success and efficiency of cryopreservation of semen from birds
or mammals differs among species and breeds or selection lines.
These differences in part relate to intrinsic “freezability” of
the semen but also result from practical issues, such as the size of
the ejaculate relative to the insemination sperm dosage, and also the
way the breeding and animal production industry is organized. In
cattle, mostly all breeding relies on artificial insemination with
frozen/thawed semen. In bird species such as chicken or Turkey,
however, artificial insemination is largely restricted to “fresh”
semen.
The fact that frozen/thawed semen is little used in commercial
fowl production has also limited the amount of research on cryopreservation methods. One reason for limited use is that the number of breeding units that can be produced per ejaculate is quite
small, certainly in comparison with, for example, bovine semen.
Wishart [19] showed that approximately 300 million sperm cells
per hen must be inseminated to achieve plateau level (>90%) fertile
eggs, in contrast to only approximately six million fresh semen.
That means that with frozen semen, only 7 hens can be inseminated
from a single ejaculate of 2 billion spermatozoa, as opposed to
300 hens when using fresh semen. Another reason lies in the
organization of the poultry industry. In cattle, selective breeding
is on the level of individual males, whereas it is being executed on
breeding line level in chicken. This makes it possible to keep males
available on site. In fact, natural mating in group housing is used in
grandparent and parent stock for the production of hatching eggs.
And if artificial insemination is used, in most cases, this is with
semen of males held on site, which can be used fresh/extended.
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Henri Woelders
Cryopreservation protocols for semen are described in the literature for a number of bird species used in animal production, as well
as for fancy and other hobby species and wild bird species.
In birds and other macrolecithal taxa, cryopreservation of the
ova or embryos is not possible. If only male gametes (i.e., semen)
can be used, it would take at least six generations of backcrossing
with frozen-thawed semen to recover a lost endangered breed or a
selection line. This makes it laborious and costly, and it is therefore
less practical. Collection, cryopreservation, and use (grafting) of
avian ovaries [5, 6] or primordial germ cells [7, 8] are potential
alternative strategies that are currently being developed. This chapter will only discuss methods for cryopreserving avian semen.
Most studies on freezing of avian semen have been done with
domestic bird species. Semen cryopreservation is described for
other domestic bird species, including turkey, duck species, goose,
and guinea fowl [9]. More recent studies or reviews have been
published, e.g., for quail [10], emu [11], guinea fowl [12, 13],
and goose [14]. Cryopreservation of nondomestic bird species was
reviewed in [15, 16]. More recent studies are, for example, for
crane species (e.g., [17]) and pigeon (e.g., [18]).
Success and efficiency of cryopreservation of semen from birds
or mammals differs among species and breeds or selection lines.
These differences in part relate to intrinsic “freezability” of
the semen but also result from practical issues, such as the size of
the ejaculate relative to the insemination sperm dosage, and also the
way the breeding and animal production industry is organized. In
cattle, mostly all breeding relies on artificial insemination with
frozen/thawed semen. In bird species such as chicken or Turkey,
however, artificial insemination is largely restricted to “fresh”
semen.
The fact that frozen/thawed semen is little used in commercial
fowl production has also limited the amount of research on cryopreservation methods. One reason for limited use is that the number of breeding units that can be produced per ejaculate is quite
small, certainly in comparison with, for example, bovine semen.
Wishart [19] showed that approximately 300 million sperm cells
per hen must be inseminated to achieve plateau level (>90%) fertile
eggs, in contrast to only approximately six million fresh semen.
That means that with frozen semen, only 7 hens can be inseminated
from a single ejaculate of 2 billion spermatozoa, as opposed to
300 hens when using fresh semen. Another reason lies in the
organization of the poultry industry. In cattle, selective breeding
is on the level of individual males, whereas it is being executed on
breeding line level in chicken. This makes it possible to keep males
available on site. In fact, natural mating in group housing is used in
grandparent and parent stock for the production of hatching eggs.
And if artificial insemination is used, in most cases, this is with
semen of males held on site, which can be used fresh/extended.
380
Henri Woelders