Genetic improvement of swine
Date
1967
Authors
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ORCID
Type
Degree Level
Doctoral
Abstract
An analysis of Canadian R.O.P. data for pigs born in
1964 and 1965 was undertaken with two main objectives in
mind. The first was the identification of genetically
superior litters and the second was the evaluation of heritability
estimates for various performance traits and of the
genetic and phenotypic correlations between them.
In order to achieve the first objective it was
necessary to investigate the various possible sources of
environmental variation since these might have masked genetic
differences. Both province and season (month or quarter)
effects were statistically significant for most traits but
the evidence favored a hypothesis that these differences were,
for the most part, reflections of genetic differences between
litters tested in the various provinces and periods. There
was evidence of a season effect on per cent ham in the
carcass and per cent lean in the ham face, but this cannot
be considered to be conclusive since data from only one year
were available.
Carcass weight was found to have an important
influence on all carcass traits including predicted yield
and it was recommended that this trait be adjusted for
carcass weight before it is utilized in a selection index.
Sex of the pig also had a substantial effect on carcass
characteristics, with gilt carcasses being superior to barrow
carcasses. Sex differences in total fat were significantly
smaller in the Lacombe breed than in the other breeds.
Consequently, the R.O.P. sex corrections overcorrected this
trait in this breed, but the sex corrections were effective
in eliminating sex differences in predicted yield. Sexes
also differed in growth rate with barrows growing faster
than gilts, especially in the Yorkshire breed. Where sib
or progeny testing is being employed and test groups are not
balanced for sex it is advisable to apply a sex correction
to age at slaughter (adjusted to a constant carcass weight)
before it is included in a selection index.
Heritability estimates were very high for all traits
except growth rate (age at slaughter). The large sire components
of variance which resulted in these high estimates
were taken as evidence for the existence of strains of pigs
which differ in average genetic merit for a given trait.
On the basis of available information, both from the
R.O.P. records studied and from the literature, recommendations
for selection procedures were made. While the
recommendations were formulated as guidelines for the
establishment of a central swine breeding station in
Saskatchewan, they should, for the most part, be applicable
to R.O.P. and other swine improvement schemes.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Animal Science
Program
Animal Science