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Animal Reproduction Science 60–61 2000 5–14 www.elsevier.comrlocateranireprosci
New opportunities in animal breeding and production — an introductory remark
I. Wilmut , L. Young, P. DeSousa, T. King
Roslin Institute, Roslin, Midlothian EH25 9PS, UK
Abstract
New opportunities in animal breeding and production will be offered by methods for embryo production and the introduction of precise genetic changes in livestock species. A review of
current procedures shows that they have been improved during the last 4 years, but still have significant limitations. In the light of experience over the past 50 years it seems likely that these
methods will contribute to animal health and productivity, but at some unknown time in the future and in ways that cannot be predicted precisely. When looking to the future, delegates to this
meeting should take pride in what science continues to contribute. q 2000 Published by Elsevier Science B.V. All rights reserved.
Keywords: Embryo; Genetic modification; Livestock; Nuclear transfer
1. Introduction
Methods for embryo production and for precise genetic modification of livestock will offer new opportunities in animal breeding and production. Progress towards those goals
has continued during the 4 years since the last of these meetings. The purpose of this analysis is to summarise progress and the present limitations before considering the
implications for the future. We are concerned only with cattle, sheep, pigs and goats.
2. Embryo production in vitro
There appears to be a contrast between ruminants and the pig in the effectiveness of Ž
. current procedures. Methods for in vitro maturation IVM of oocytes, fertilisation and
Corresponding author. Tel.: q44-131-527-4219; fax: q44-131-527-4493. Ž
. E-mail address: ian.wilmutbbsrc.ac.uk I. Wilmut .
0378-4320r00r - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 3 7 8 - 4 3 2 0 0 0 0 0 1 4 2 - 1
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embryo culture have been used extensively in cattle Leibfried-Rutledge et al., 1989 Ž
. and sheep Walker et al., 1992 . The methods are also being used in cattle breeding
schemes after aspiration of oocytes from selected females and to produce calves from casualties. By contrast, despite a considerable research effort and the introduction of
several novel steps, only a very small proportion of pig oocytes developed to offspring Ž
. Prather and Day, 1998 .
In the past, development was perturbed in some ruminant offspring produced in vitro Ž
. reviewed by Young et al., 1998 . The most obvious symptom is an increase in
birthweight, to an extent that may be sufficient to prejudice survival of mother and offspring. Although pregnancy is extended this is not the cause of the large size as
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differences arise early in pregnancy see Young et al., 1998 . Not only are some offsprings unusually large, but the weight of the liver, kidney and heart is sometimes
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disproportionally large Sinclair et al., 1999 and there is an increased incidence of developmental abnormalities. Expression of imprinted genes is being studied in the light
of the similarities between the Large Offspring syndrome in livestock, children with congenital abnormalities such as Beckwith–Wiedemann syndrome and mice with tar-
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geted changes in their genes see Young et al., 1998 . Embryo transfer can be used much more efficiently if there is a method for embryo
storage. Otherwise a large group of potential recipients must be available and these increase the cost very markedly. While cryopreservation of cattle and sheep embryos has
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been achieved and is widely used Rall, 1992 , in the other species, it is still in the developmental stage. In particular, pig embryos are very sensitive to chilling injury.
Recent experiments show that useful survival of pig embryos could be obtained if their Ž
. lipid content was reduced before vitrification Dobrinsky et al., 1999 .
Further research is needed to provide methods for embryo production and storage in pigs and to make those in ruminants more efficient. After culture, the embryos must also
be capable of normal development to term.
3. Nuclear transfer
