Redesigning Animal Agriculture

7 Cloning and Transgenesis to Redesign
Livestock
D.N. Wells 1 and G. Laible 1
1 Reproductive Technologies, AgResearch Ltd, New Zealand
Abstract
An efficient animal cloning technology, using the procedure of nuclear transfer (NT), would provide many
opportunities for livestock agriculture and biomedicine. Although the birth of ‘Dolly’, the first animal to
be cloned from an adult cell, occurred back in 1996, it is still remarkable that NT using differentiated
donor cells can produce physiologically normal cloned animals. But the process is very inefficient, poorly
understood and appears highly prone to epigenetic errors resulting in abnormal phenotypes. Importantly,
it appears that these deficiencies are not transmitted to offspring following sexual reproduction. This
provides initial confidence in the first application of NT in agriculture, namely, the production of small
numbers of cloned sires from genetically elite males, for natural mating, to effectively disseminate genetic
gain. The continual advances in animal genomics towards the identification of genes that influence livestock
production traits and impact on human health serve to increase the ability to genetically modify
cultured cells, prior to NT, to generate livestock with increased productivity or that produce superior
quality food and biomedical products for niche markets. The potential opportunities for animal agriculture
are more challenging because of the greater demands on cost, efficiency, consumer acceptance and
relative value of the product for commercial viability in contrast to biomedicine, which is the main driver
for this technology platform. None the less, cloning and transgenesis are being used to redesign the genetic
make-up of livestock; however, the integration of this technology into practical farming systems remains
some time in the future.
Introduction
In this review, the current somatic cell
cloning technology, its efficiency, present
limitations and potential applications,
especially in combination with transgenesis,
to re design livestock animals for agriculture
and biomedicine is discussed, along
with some of the challenges for adoption of
these controversial technologies. The main
emphasis is placed on cattle and also the
other commonly farmed livestock species
such as sheep, goats and pigs, but excludes
poultry and fish. Relevant data from mouse
models, which aid our understanding of the
biology and consequences of nuclear cloning
and transgenesis, are also presented.
The embryo manipulation procedure
termed nuclear transfer (NT) is the most
dramatic method of producing cloned
animals because it effectively generates a
viable animal from an individually selected
cell (Wilmut et al., 2002). Using a microsurgical
approach, the nucleus of a donor cell
is typically transferred into the cytoplasm
of a mature oocyte following removal of its
©CAB International 2007. Redesigning Animal Agriculture
94 (eds D. Swain, E. Charmley, J. Steel and S. Coffey)