Today, more than 90% of artificial inseminations (AI) in
pig production around the world are carried out with
extended liquid semen stored for a period of up to 5 days
[1,2]. Semen processing involves dilution and cooling of
the boar ejaculate to a storage temperature between 15 C
and 17 C. Dilution and temperature management of
freshly collected boar ejaculates are the main factors
influencing sperm cell function and resistance to Boar sperm membranes have a lower concentration of
cholesterol and are thus rendered more labile to chilling
than spermatozoa from other species [6]. AI centers have
to consider the high susceptibility of boar spermatozoa to
chilling injury for minimizing harmful effects that might
compromise fertility of the processed and stored semen.
Essentially, two different dilution procedures have been
established in AI practice for producing the required
amount of insemination doses, that is, one-step and twostep
dilution. In the one-step procedure, boar spermatozoa
are diluted isothermally within 30 minutes after
collection to the final volume with the extender preheated
to approximately 32 C. In the two-step procedure, boar
semen is at first diluted in a ratio of 1:1 or 1:2 (v:v) at
approximately 32 C, followed by a final dilution with either
an extender at about 32 C (two-step isothermic) or a
hypothermic extender kept at 21 C to 24 C (two-step hypothermic)
[9]. The most recently introduced protocol boar
stud practice is the two-step hypothermic procedure with
the aim of facilitating semen processing by bringing semen
doses faster to the desired storage temperature [10].
It is not yet clear, however, whether semen quality is
compromised by the two-step dilution in conjunction with
a rapid drop in temperature, as currently used for routine
semen production in boar studs. Literature on the effects
of temperature management on boar semen quality during
semen processing is scarce. Somewhat surprisingly,
two previous studies measuring standard semen parameters
and calcium influx did not find an effect of dilution
temperature in two-step semen processing on semen
quality during 48- to 72-h storage at 17 C [4,5].
In the present study, we evaluated the effect of temperature
in boar semen processing both under experimental
and under field conditions. Experimental
conditions were highly standardized considering temperature
kinetics and potential influence of extenders. In the
field study, semen quality data from 23 European boar
studs that participated in an external quality control program
were related to each stud’s temperature regimen
during semen processing. Our hypothesis was that
two-step hypothermic processing of boar semen results
in lower semen quality compared with isothermic
processing.