Redesigning Animal Agriculture

health, fitness and behaviour of these transgenic
animals throughout their lifetime as
part of their higher standard of management
and care (Van Reenen et al., 2001).
Industry Adoption
Even, if at some time in the future regulatory
approval and substantial public acceptance
is gained, the prospect of incorporating
transgenic animals into herds and flocks
will pose challenges for animal industries,
particularly if products still need to be segregated.
This could be most difficult for
dairy industries where milk is pooled and
handled in bulk; it might be somewhat
easier with meat and fibre products with
individual animal identification and easier
product segregation and traceability.
Milk is a commodity product which is
processed by high-capacity facilities into a
range of different products. Particular transgenic
milk streams, tailored for specific
purposes, might be unsuitable for general
commodity dairy products. Modifying milk
composition to benefit cheese manufacture
for instance (Wall et al., 1997; Brophy et al.,
2003) would be to the detriment of some
other processed foods. Whilst the specific
staphylolytic activity of lysostaphin used
to engineer cows with resistance to mastitis
(Wall et al., 2005) is unlikely to affect
the microorganisms used to manufacture
dairy products, more general anti-microbial
agents such as lysozyme or lactoferrin
might do so. Conversely, however, they
might slow the growth of bacterial contaminants
in the milk, increasing the shelf-life
of certain dairy products (Maga et al., 2006).
The over-expression of specific proteins
might be at the expense of other endogenous
milk proteins (Brophy et al., 2003)
and may affect the composition of the milk
and hence its physicochemical and manufacturing
pro perties (Maga et al., 2006) in
sometimes unanticipated ways. The point is
that at present, through our limited understanding,
the consequences of even simple
genetic modifications on other characteristics
of a complex biological fluid like milk,
Cloning and Transgenesis 111
and the products derived from it, cannot be
fully predicted and require rigorous evaluation
in each instance. This prolongs the time
before there would be any prospect of a particular
genetic modification being introduced
into the marketplace and the improvement
afforded by the genetic modification would
have to be substantial to compensate for
this. This would be less important in situations
where specific high-value endogenous
milk components are over-expressed and
extracted from the milk for the food ingredient
or nutraceutical markets.
One possible scenario for the future is
the generation of herds possessing different
specific genetic modifications to tailor agricultural
products for niche markets. In the
dairy industry, transgenic milk from specific
herds would need to be kept separate
for manufacturing purposes, let alone for
food-labelling compliance. Such a prospect
would pose challenges for the structure of
traditional commodity-based dairy industries
processing bulk milk. The integration
of transgenesis might necessitate regional
herds producing milk of a similar type
with specific processing capability available
locally. Perhaps more importantly for
adoption of the technology at an industry
level, farmers need to be paid according to
the specific products they are producing
behind the farm gate.
The most efficient means of introducing
a desired genetic modification into
the wider livestock population is through
low-cost artificial insemination or natural
mating using transgenic males. It is
a particular advantage of the cell-mediated
transgenic approach that the genetic
modification can be made on an already
outstanding genetic background by using
cells from an elite male. Ideally, the sire
should be homozygous for the desired trait
so all progeny receive a copy of the transgene.
For widespread agricultural applications
of gain-of-function transgenes, it is
considered important that the integration
site be well characterized and tested in
hemizygous and homozygous states on a
range of genetic backgrounds, as this can
affect the phenotypic outcome in different
breeds or strains (Siewerdt et al., 1999;