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Abstract
The present study tested the field fertility of frozen-thawed (FT) Swedish boar semen
packaged in flat plastic containers (FlatPacks) and exported for artificial insemination
(AI) to overseas nucleus herds. Semen from 47 Swedish boars of Landrace (L), Yorkshire
(Y), and Hampshire (H) breeds was frozen using a lactose-egg yolk-based extender with
3% glycerol and 10(9) spermatozoa/ml in 5 ml FlatPacks. For all breeds, FT sperm membrane
intactness averaged 60%, while mean FT sperm motility ranged from 49 to 53%. A total
of 308 litters resulted from 421 overseas inseminations with FT semen, with a mean
farrowing rate (FR) of 73% and 10.7 mean number total piglets born. In a within-sow
analysis for the purebred L and Y breedings, the FR and litter size of FT semen were
compared with natural matings (NM) and on-farm AI with liquid semen (NW/AI breedings)
at the same farms. Farrowing rate was 72.3 and 78.8% (P = 0.23), total piglets 11.3
and 11.6 (P = 0.44), and live piglets 10.1 and 10.2 (P = 0.77), for the FT semen and
NM/AI breedings, respectively. The present results suggest that this freezing protocol
and FlatPack container maintains high sperm viability post-thaw. Further the fertility
levels when inseminated at overseas nucleus herds seem to be similar to those achieved
with (NM/AI breedings) at the same farms. This freezing method may be a reliable alternative
for the freezing/thawing of boar semen under commercial AI conditions.