Agriculture Reference
In-Depth Information
Ocean-based net pen aquaculture has supplied
the growth of the salmon supply since that time.
It has been calculated that an extra 52 mMT of
aquaculture production will be needed by 2025
if the current rate of fish consumption is to be
maintained (Fletcher et al ., 2004). Selection for
fast-growing fish using conventional breeding
results in a shift in the allele-frequencies of
many growth-associated genes. Farmed fish
have been shown to have a fitness disadvantage,
called a genetic load, in natural environments
because domestication genes are only favourable
in domesticated environments. Interbreeding
between escaped farmed salmon and wild native
fish can result in a 'substantial risk of extinction
for natural populations' (Lynch and O'Hely,
2001). In principle, there is no difference
between the types of concerns and potential
magnitude of the environmental risks associ-
ated with the escape of growth enhanced GE
salmon and those related to the annual escape
of the millions of farmed Atlantic salmon that
are genetically divergent from native popula-
tions in other ways, e.g. strains selected for
enhanced growth (Schiermeier, 2003). Given
these concerns a case could be made that raising
GE salmon in contained land-based tanks is a
more sustainable approach to salmon aquacul-
ture than the ocean-based net pen aquaculture
systems that currently supply over half of the
world's salmon market.
Other examples of GE animals that have
been developed for agricultural applications may
also contribute to sustainability. Transgenic ani-
mals have been developed for disease resistance
(Wall et al ., 2005) and environmental benefit.
For example, the GE 'Enviropig' has decreased
levels of phosphorus in its manure because it
produces the enzyme phytase in its saliva, and is
therefore able to metabolize dietary phytate
(Golovan et al ., 2001). Given the large increase
that is expected in both pig and poultry pro-
duction in the developing world over the next
20 years as a result of the 'livestock revolution'
(Delgado, 2003), decreasing the phosphorus
levels in the manure of these monogastric spe-
cies would likely have a huge worldwide envi-
ronmental benefit. A number of researchers
(Flint and Woolliams, 2008; Fahrenkrug et al .,
2010; Hume et al ., 2011; Niemann et al ., 2011)
consider that GE animals 'can and will provide
many of the solutions for tomorrow's agriculture'
(Hume et al ., 2011). The current regulatory and
political roadblocks to this technology are pre-
venting its adoption in the developed world, but
several developing countries are aggressively
pursuing the development of GE animals to help
provide a source of animal protein for their
growing populations.
Generation Interval
We are currently entering an era where DNA
technology will likely expand the repertoire of
traits that can be addressed by breeding (Flint
and Woolliams, 2008). Because GS offers an
opportunity to improve the accuracy of EBV of
young animals, it provides an approach to
decrease the generation interval. It is for this
reason that GS has experienced such widespread
and rapid adoption in the dairy breeding sector
where the need to determine the BV of a young
bull typically involves waiting for milk produc-
tion records from his daughters. This increases
the male generation interval considerably com-
pared with a BV estimate that can be obtained
from a DNA test of a newly born calf. For exam-
ple, in dairy populations the rate of genetic
improvement is expected to double with the
application of GS (Hayes et al ., 2009a).
GS may also offer selection criteria for traits
that are not currently considered in BO due to an
absence of objective, quantifiable measures
upon which to base selection decisions. The GS
approach is clearly attractive for difficult to
measure traits such as reproductive success and
longevity in varied environments, efficiency of
nutrient utilization, animal temperament, stress
susceptibility, innate resistance or susceptibility
to disease, adaptability, and reduced GHG emis-
sions. Hayes et al . (2009b) demonstrated how
GS could be used to breed cattle better adapted
to an environment altered by climate change.
Preliminary results from the poultry industry
suggest that GS focused on leg health in broilers
and liveability or viability in layers can rapidly
and effectively improve animal welfare (Cheng,
2010). In theory, GS offers the opportunity to
provide DNA-based selection criteria for multi-
ple sustainability traits simultaneously.
Considerable investment in both genotyp-
ing and phenotyping will be required to develop
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