Animal Biotechnology Science-Based Concerns (2002) / Chapter Skim
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6. Animal Health and Welfare
6. Animal Health and Welfare
Pages 93-107
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From page 93... ...
REPRODUCTIVE TECHNOLOGIES Reproductive manipulations, including superovulation, semen collection, artificial insemination (AI) , embryo collection, and embryo transfer (ET)
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From page 94... ...
For example, a method has been devised for non-surgical embryo transfer in pigs, and ova for some purposes can be obtained from slaughterhouses, which eliminates the need for manipulation of live donor livestock females. The use of nuclear transfer to produce transgenic animals could eliminate the problem of repeated elective abortion and reuse of recipient animals, since cell populations with specific genotypes or phenotypes could be selected before embryo reconstruction (Eyestone and Campbell, 1999~.
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From page 95... ...
LOS animals have more congenital malformations and higher perinatal mortality rates, although the incidence and severity of the effects reported vary widely among studies (Van Reenen et al., 2001~. The range of abnormalities reported includes skeletal malformations (Walker et al., 1996)
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From page 96... ...
is under development for fertilizing livestock embryos (Chapter 1) , and ICSI procedures have been combined with microinjection to produce transgenic animals (Perry et al., 1999~.
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From page 97... ...
And because many insertional mutations are recessive, their effects do not become obvious until the animals are bred to transgenic relatives (Chapter 2~. For example, although mice engineered with a transgene for herpesvirus thymidine kinase were normal, their offspring that were homozygous for the transgene had truncated hind limbs, forelimbs lacking anterior structures and digits, brain defects, congenital facial malformations in the form of clews, and a greatly shortened life expectancy (McNeish et al., 1988~.
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From page 98... ...
Similar problems are seen in mice transgenic for human growth hormone (Berlanga et al., 1993~. Problems due to growth hormone expression also can be seen when the inserted gene comes from the same, or a closely related, species.
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From page 99... ...
In most cases, deleterious phenotypic changes in transgenic farm animals particularly animals transgenic for growth hormone or other growth promoting factors have been easy to detect because they cause such gross pathologies. However, more subtle effects also are possible.
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From page 100... ...
Mice transgenic for an immune system regulatory factor, interleukin 4, develop osteoporosis, but not until about two months of age (Lewis et al., 1993~. This emphasizes the importance of monitoring the welfare of founder transgenic animals, and sometimes successive generations, throughout their lifetime using multiple criteria, including behavioral abnormality, health, and physiologic normality (Van Reenen et al., 2001~.
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From page 101... ...
Clones produced by fusion of nuclear donor cells with unfertilized eggs are not identical twins, but "genetic chimeras," since almost all cloned livestock studied to date have mtDNA from the recipient egg but not from the donor cell (Evans et al., 1999; Takeda et al., 1999~. Whether or not there are potential adverse effects on health and welfare due to having nuclear DNA from one source and mtDNA from another are unknown, although mitochondria are responsible for important cellular functions and mitchondrial type theoretically could affect relevant production traits as well.
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From page 102... ...
BIOMEDICAL APPLICATIONS In contrast to genetic manipulation of farm animals for production traits, transgenic manipulation for the production of human pharmaceuticals or transplant organs generally is not intended to cause changes that have physiologic effects on the animals themselves. Thus, although unexpected and undesirable phenotypic effects still can occur as a result of gene insertion or cloning technology, there generally are fewer potential animal welfare concerns associated with the production of transgenic farm animals for biomedical purposes than for agricultural purposes (Van Reenen and Blokhuis, 1993~.
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From page 103... ...
No phenotypic abnormalities have been reported in pigs as a result of the expression of transgenes for these human proteins, although, since the pigs are produced by microinjection, there are the usual inefficiencies in terms of the number of embryos microinjected relative to the number of transgenic animals born (Tu et al., 1999; Niemann and Kues, 2000~. Research is underway to produce pigs that, in addition to carrying complement transgenes, have both copies of the gene encoding the enzyme that produces the antigen associated with rejection knocked out.
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From page 104... ...
and neurodegenerative disease (Theuring et al., 1997~. As genetic engineering techniques for farm animals improveparticularly such that single base coding changes that are typical of many human genetic diseases can be introduced, and the production and use of farm animal models becomes more economically feasible it is likely that more models for disease research and toxicity testing will be developed.
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From page 105... ...
has proposed the use of the 'principle of conservation", which states that transgenic and cloned animals developed for agricultural uses should not be worse off than the founder animals or other livestock of the same species under similar housing and husbandry practices. POTENTIAL ANIMAL WELFARE BENEFITS Genetic engineering certainly has the potential to improve the welfare of farm animals.
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From page 106... ...
; COSTS VERSUS BENEFITS In making assessments about the production of genetically engineered animals for farming, costs and benefits need to be weighed carefully. When expression of growth hormone is regulated appropriately in transgenic pigs, for example, the increases shown in growth and feed efficiency are modest, and are similar to the increases that can be attained simply by injecting pigs with porcine growth hormone (Purser et al., 1989, Nottle et al., 1999~.
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From page 107... ...
On the one hand, cloning by its nature produces identical copies of a particular individual, reducing genetic variability relative to what would have been transmitted via conventional breeding. On the other hand, cloning makes it possible to save and utilize genetic variability that would not otherwise be available.
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