P . Visscher et al. Livestock Production Science 65 2000 57 –70
65
1998 concluded that using crossbred information in sequence. Driven by human medicine, these tech-
a poultry breeding programme was superior to using nologies are probably not far away, perhaps only 5
pureline information only if the ratio between domi- years or so. Surely the livestock industry will utilise
nance variance and total genetic variance was ap- advances in such technologies, and should be pre-
proximately 0.3 or higher. Note that the increasing pared to use the information which is generated by
spread of A.I. in the pig also means that elite boars them.
from the nucleus level would also have offspring at the commercial level, so their information would be
3.5. Genetic modification technologies available at the moment when their half sib groups in
the nucleus level are to be selected. Although In this review, we have concentrated on reproduc-
technology may already be available to implement tive and molecular technologies which do not alter
such a structure, it is likely to need a massive the genome other than through the standard pro-
investment in the infrastructure to allow data of cesses of selective breeding. The reason for not
guaranteed quality to be retrieved from all levels of discussing transgenic or genetic modification tech-
the breeding structure. nologies in great length is because it is unlikely, in
our opinion, that these technologies will be used for 3.4. Genetic marker technology
pig improvement in the next 5–10 years. This prediction is based both on technological and con-
For some of the schemes suggested above, cheap sumer attitude arguments. In our opinion, genetically
genomic information, for example in the form of a modified meat is not likely to be acceptable to the
dense marker map, would be advantageous. Is this a consumer in the near future. The technological
realistic scenario for the livestock industries? We problems and prospects were recently discussed by
think it is, for a number of reasons. Firstly, the Pursel 1998, and are related to which genes to
current marker technology of choice, i.e. microsatel- target, and how to control the expression of genes
lite markers i.e., markers based on genetic variation which have been introduced.
in the number of repeat sequences at a particular locus, is relative new since the late 1980s, and new
technologies which could overtake them have been
4. Combining several techniques: speed genetics
developed and are being developed. In particular, in plant and some animal studies, amplified fragment
The real impact of biotechnology will come from length polymorphisms AFLPs are now routinely
combining new reproductive techniques with power- used to genotype individuals quickly with a battery
ful molecular techniques. The former will allow a of markers. From studies in human and mouse, it
rapid turnover of generations, whereas the latter can appears that the method of choice will soon be single
provide selection which does not need phenotypic nucleotide polymorphisms SNPs. A polymorphic
information when the selection decisions are made. marker is a locus at which different alleles are
Georges and Massey 1991 suggested speeding present in the population, i.e. for which alleles are
up genetic progress in cattle through ‘velogenetics’, segregating. A SNP is a marker at a particular DNA
by harvesting oocytes from calves in utero, thereby nucleotide where different alleles are due to single
reducing generation intervals substantially. Using base changes. The advantage of SNPs is the abun-
markers in such a scheme, which could also be dance approximately one SNP every few hundred
applied to pigs, would allow rapid selection based base pairs, so potentially millions of polymorphisms
solely upon markers, for example in an introgression for the pig genome and the possibility for complete
programme Fig. 4. One cycle of selection start with automation using DNA array technology. Moreover,
the maturation of immature oocytes from suitable the technology is unlikely to stop with SNPs. Ulti-
donors, followed by in vitro fertilisation. Implanta- mately we will be dealing with complete sequences
tion of embryos is then carried out, using suitable of individuals, by automatically scoring only those
recipients, for example those with large uterine polymorphisms which differ from some pre-defined
capacities. As before, although we have used the
66 P
. Visscher et al. Livestock Production Science 65 2000 57 –70
Fig. 4. Velogenetics using IVEP.
Meishan as an example, suitable recipients could be gene introgression programmes for which no addi-
from other sources e.g., improved white lines, tional phenotypic information is required.
crosses between Chinese and European pigs. After If we allow ourselves to imagine that the technolo-
the piglets are born, they can be selected immedi- gy will develop to a stage where cell differentiation
ately using marker assisted selection, and immature can be controlled in vitro we can imagine that in
oocytes can be harvested from the selected female vitro meiosis followed by fertilisation may become
piglets. The duration of one cycle of selection of possible Fig. 6. Utilising this would allow for very
such a rapid selection programme is about 4–5 rapid introgression, or with high-density marker
months. The disadvantage is that the breeder has to maps and knowledge of marker–QTL associations,
wait until the piglets are born before MAS is applied. more generalised selection objectives e.g., Haley
It is assumed here that the loss of embryos would be and Visscher, 1998. For example, introgression of
too great if MAS is attempted on the early embryos. fertility QTLs from exotic breeds could be performed
The combination of MAS and such embryo tech- entirely in vitro, thereby reducing the total time of an
nologies could be further enhanced by technologies introgression programme to months rather than
currently under development, such as nuclear trans- years.
fer Wilmut et al., 1997. In comparison to ‘stan- dard’ velogenetics, we can now apply marker as-
sisted selection on a diploid cell line, after in vitro
5. Discussion and conclusions
