`VALUE ADDED' ANIMALS: WHAT IS ON THE HORIZON? WHY GENE-TAILORING ANIMALS ISN'T EASY
Boston — Animal scientist Neal First is enthusiastic about the potential of genetic engineering. But the University of Wisconsin biologist notes that there's more to it than just laying out the genetic blueprint for a better chicken or a superior cow. As things stand now, genetic engineers can insert new genes into sheep, pigs, and other species and have them become part of an animal's genetic makeup. Yet the results aren't always what they expect. Thus, for animal scientists the challenge of genetic engineering is also a challenge to learn more about creatures with which they have long been familiar. In the process, they are exploring techniques of reproduction that may help preserve rare species.
Dr. First explained this challenge in a telephone interview.
How soon can we expect the supercow?
I think the potential is very high in terms of tailor-making livestock to what the consumer market situation and the economic situation is at a particular time. We have to remember that, because we're doing this through the genetics of the animal, the time interval for a species with long generation intervals is going to be long. And so it's going to take a long time to understand by experimentation the process we want to change, even after we've made the transgenic animal. And then it's going take an even longer time before we actually have those genes in an animal ... [that is in] high production....
Does this take longer than normal breeding?
No, it doesn't take longer than normal breeding. But you have to have a normal breeding cycle to do the tests - at least one, maybe two. And then you have to have a normal breeding cycle in order to produce the animal. And then, if you only produce one or two [animals], you have to have quite a few normal breeding cycles or some propagation method like artificial insemination to bring them up to [useful] numbers ....
In species that propagate rapidly, you can do those things very quickly - for example, the mouse. For species that propagate slowly, you want to be pretty sure before you start, because it's going to be many years before you get done.
What's the best species to start with?
I think that the species differ in this respect. For species that are multi-offspring litter bearing like the pig, where you can get a lot of eggs and the cost isn't very high, the chances of doing modifications with the techniques that exist now are pretty good. And they're being done. For a species like cattle, where the value of the embryo is extremely high ... and the [gene transfer] methods are not very efficient, the prospects are going to be much slower.
So I guess our approach is that we need better methods.
What sort of methods?
Well, the methods that are needed are really in the area of better methods for [gene] transfer. The inefficiencies fall in two parts. They fall in part in doing the transfer of the gene - getting it integrated and expressed [in the animal]. But they also fall in the reproductive steps - how to go from one cell to an animal.
So if that embryo is extremely valuable, you don't want to risk the chance that it's not going to survive [because of] something you're going to do to it. And I think that's going to be a limitation.
Are pigs the best animals to work with right now?
Because the pig is litter-bearing and it has short gestation and its reproductive characteristics are such that you can get a lot without a lot of cost, you could use inefficient methods and still make them work.
What improvements are we actually talking about? Is it better food value in meat, disease resistance, more milk production?
You're probably talking about all of those eventually.
I don't know [which will be first]. And I say that in all honesty, because the first genes, of course, that people were putting in were genes that involved growth and feed efficiency. But there have been genes placed in animals now for disease resistance. And some of those have gotten to the testing stage....
What's going to be useful will come out of an understanding of the animal's physiology and predicting results, to determine if it [gene transfer] makes a predicted change. For example, we might want more tender beef. So we're going to target something in the skeletal muscle.
Is that why you say genetic designers need to know more about animal physiology?
It's really understanding the animal's physiology and the [targeted] process. And that's what happened with the growth hormone problem. When growth hormone was put into pigs and sheep, I think, we just learned we really had to understand more about how animals do regulate their growth. It clearly wasn't growth hormone alone [that regulated growth].
How seriously should one take such spectacular experiments as the goat/sheep chimera - the GEEP? Are these just stunts?
Well those have been done. They're serious to the point of somebody wanting to get some answers from them. So they're not just a stunt. They come, for example, from the idea that those kinds of experiments allow us to have a species maintained in the uterus of another species. And that's important for exotic animals. So we have the basic ability to raise extinct, or nearly extinct, species of sheep and goat, for example, in a domestic sheep.