Utilizing animal gene resources

by U.B. Lindström

Lately it has become fashionable to talk about “synthetic breeds,” or simply about “synthetics”. What do we mean by this expression? Webster's seventh new collegiate dictionary defines “Synthetic” as something “…produced artificially… something man-made… to imitate or replace usual realities.” This suggests that making synthetic breeds is comparable to making synthetic fibres from oil. Unfortunately — or perhaps fortunately — this is not so. We cannot yet take the required ingredients from the shelf, mix them in the correct proportions and create a synthetic animal. On the other hand, recent spectacular advances in gene manipulation (Cohen, 1975) suggest that in the future we may well be able to combine genes from widely differing sources, and even from completely unrelated species.

At present, however, it seems preferable to talk about new breeds and reserve the word “synthetic” for situations where it is better suited. A new breed is one which is created by selecting and combining genes from available breeds and strains. This article deals generally with making use of gene resources, and is not restricted to the creation of new distinct breeds. An excellent discussion of the utilization of breed resources is provided by Dickerson (1969, 1974).

Why new breeds?

We can conveniently start by asking: “Is there any need for new breeds?” The successful creation of new breeds in recent times (e.g., Lacombe and Minnesota pigs, Corriedale and Columbia sheep, Santa Gertrudis and Jamaica Hope cattle) could perhaps be taken as an indication of a real need for more work in this field. But how much worse off would we have been if these new breeds had never appeared? It is difficult to say because experimental evidence is very scant. In any event, there seems to have been a demand for some of the new breeds, and we cannot without proof condemn them as useless. In the developing countries the creation of new breeds certainly offers real advantages. For example, the Dorper sheep breed in South Africa, from a cross between Dorset Horn and Blackhead Persian, has proved very useful in Kenya (de Haas, 1972). Thus, new breeds may be able to fit into niches that otherwise would remain empty.

The author is with the Agricultural Research Centre, Institute of Animal Breeding, Box 18, 01301 Vantaa 30, Finland.

Advantages

However, it should be stressed that before starting to make a new breed by utilizing several gene pools, one should be fairly confident that it offers some advantages. Among the possible advantages of combining several gene pools are:

1. increase in selection differential;

2. decrease in rate of inbreeding;

3. increase in genetic variation;

4. rapid improvement in some specific trait;

5. heterosis in the first generations;

6. increased efficiency of operations in one population (compared to work in several small ones).

There is no doubt that theoretically some of these advantages might be substantial. In practice, however, it is not as clear. For example, how important is a higher selection differential in cattle, pigs and sheep when so far we have rarely been able to utilize even the selection potential within existing breeds? And is the fear of inbreeding in our major livestock populations (in Scandinavia, for example) anything but a ghost we every now and then take out of the closet to scare each other with? The possible increase in genetic variation might be very useful, but on the other hand there is no evidence that we are running out of genetic diversity, with the possible exception of some poultry populations (Lindström, 1969). The greatest gain in using foreign populations is the possibility of quickly introducing superior genes for a trait where the domestic population is clearly inferior.

If heterosis is of importance in species with a high rate of reproduction, continuous crossbreeding is to be preferred to a combination of gene pools (Dickerson, 1969). In cattle — especially dairy cattle — and sheep, there is much more room for the creation of new breeds. Finally, the smaller the breed is numerically, the stronger is the case for putting its genes into the same basket with those of other populations.

Drawbacks

As is evident from the previous reasoning, there are also drawbacks in combining several gene pools. Among possible disadvantages are:

1. loss of non-allelic (epistatic) gene effects;

2. introduction of undesirable genes into the population;

3. disturbance of breeding and selection work with a decreased accuracy of testing in the first generations;

4. loss of crossbreeding possibilities;

5. increased risk of introducing diseases;

6. increased risk of losing genes that may be needed later.

We should not be too worried about the loss of epistatic gene effects (Kempthorne, 1954). Neither is there reason to believe that the risks of losing potentially valuable genes or introducing diseases are of overwhelming importance. The loss in crossbreeding possibilities is, of course, real, but its importance depends greatly on the available assortment of potentially useful breeds (Skjervold, 1970). In cattle this problem would seem to be of less importance than in poultry and pigs, although the indiscriminate spread of the Friesian breed all over the world cannot, in the long run, be regarded as wholly desirable.

Vision of future possibilities of making synthetic animals

Practical difficulties

On the other hand, it is always risky to introduce genes from another population, simply because one does not know exactly what one is getting. It is therefore vital that a carefully planned procedure of selection and evaluation be followed in utilizing foreign populations (see Figure 1). By restricting importation to samples of rigorously tested animals, much (although not all) of the uncertainty can be eliminated. This is what is done in Norway at present in evaluating various dual-purpose cattle populations (Skjervold, 1974).

Finnsheep ewes on pasture. The breed's high prolificity has gained attention only recently

If the development of a new breed (introduction of foreign genes) is left to individual speculators or breed societies with selfish interests, much harm may be done. In Finland, for example, the introduction of the Friesian breed was made in a manner that resulted in the splitting up of the cow population into unnecessarily large subgroups of pure- and crossbred animals, with repercussions for the progeny testing efficiency within breeds. In 1973–74, Friesian bulls were used on 7 to 10 percent of recorded cows of the Ayrshire and Finncattle breeds. This is, of course, a transitional stage which in the long run may be of little practical importance. Nevertheless, a too rapid dissemination of untested genes involves risks that can easily be avoided by better planning.

What kinds of animals?

Paul Valéry once said: “The only trouble with our time is that the future is not what it used to be.” The energy crisis, food shortages and economic recessions in recent times have made all predications of future requirements more uncertain than ever before. This is also true for animal production, and should seriously be taken into account when discussing what kinds of animals will be needed in the future. In this connexion we can ask the following questions:

1. What species and how many animals of each will we need in various areas?

2. What kinds of breeds (genes) will we need within the next 15,30 and 60 years?

3. How good is our knowledge of different breeds?

4. Will there be a growing need for breeding animals resistant to difficult conditions and diseases?

5. Will there be barriers to a free exchange of genetic material?

6. Will mutagenesis, sex control and egg transfer be of any importance?

It would be presumptuous even to pretend to know all the answers, but the following views would be relevant.

Ruminants and other animals

With increasing pressure on farmland to supply the world's growing population with food, it seems probable that times will be much tougher for monogastric animals than for ruminants. Therefore, each country would do well to take a closer look at its possiblities and priorities in maintaining various animal species. Obviously, the numbers of the various species might influence the kinds of breeds that are needed. For example, if the pig population in Finland were drastically reduced, what consequences would it have for our cattle breeding policy? Would we have to put more emphasis on beef breeding or would we simply have to make do with a much reduced per caput consumption of meat?

Even if it does not seem probable at present, there might in the future be barriers to the exchange of genetic material. A policy of importing small samples (preferably semen) of breeds that might come in handy some time in the future should be favoured. The importation and storage costs would be negligible compared with the possible benefits from this kind of genetic “insurance policy.”

Mutagenesis and sex control

The prospects of achieving results by mutagenesis in large animals are still poor (Bomsel-Helmreich, 1974), and cannot be expected to contribute much in the near future. Is this because it cannot be done, or because we are not trying hard enough? Egg transfers are already a reality, and may, even within 5 to 10 years, begin to play a practical role. Almost every year someone claims to have solved the problem of sex control, but in practice little gain seems to have been achieved (Beatty, 1973).

If predetermination of sex becomes possible, it would certainly influence breeding policies, especially in species with low reproductive rates. The effects would be similar to those of large-scale egg transplantations: when fewer females are needed for replacement, a larger proportion of the population could be utilized for specialized and crossbreeding purposes. Consequently, there would be less need for multipurpose breeds. For example, in cattle there would be improved possibilities of producing the required number of meat animals from specialized beef breed × dairy female crosses (Cunningham, 1975), resulting in reduced demand for dualpurpose sires. Similarly in sheep, improvements in egg transfer and sex determination techniques would promote crossbreeding systems related to those practised in present-day pig production.

What is available?

Although it is hazardous to predict what will be needed within the next 30 or 60 years, the following trends appear likely:

1. Feed efficiency will be of increasing importance in all species.

2. Fertility traits will be given more attention, especially in cattle and sheep.

3. When breeds and individuals are evaluated, considerably more emphasis will be put on overall economic merit. Although a discussion of this point is outside the scope of this article, an example is provided in Table 1.

FIGURE 1. Schematic outline of steps in gene resource evaluation

Let us look at these statements from the point of view of utilizing available gene resources. First, it is evident that we really do not know enough about the merits of various breed groups, even those in our neighbouring countries. A good example is the sudden interest in Finnsheep. Records of this breed's prolificity have been available since the 1920s, but it was only in the 1960s (after K. Maijala drew attention to them) that breeders elsewhere became interested. Is it not probable that there are still several very useful breeds in all species that we have not even considered as potential gene resources? At present, it seems that increasing interest is being shown in the French and Italian beef breeds. It is encouraging to see that we are finally beginning to look for genes all over the world, for there is no doubt that we can still derive much benefit from this.

Dorper ewe. The breed can adapt to harsh conditions and is more productive than many indigenous breeds in Africa

Feed efficiency

Feed efficiency is one trait where screening of foreign populations might be very rewarding. Are there differences in feed conversion between breeds? If there are, how large are they? Our knowledge in this field is far from complete, and solid experimental evidence is hard to come by. For example, are there any differences between the pig breeds of Europe and those of the Far East in this respect? Is it naïve to think that there might be exploitable differences between, for example, the pig breeds of China (which live to a great extent on waste products) and our own breeds? In both dairy and beef cattle there are indications that real differences in feed efficiency exist between breeds (Cundiff, 1974; Dickinson et al., 1969; Henningsson and Brännäng, 1974), but more evidence is badly needed. So far, we have been content to rely on the high genetic correlation between production and efficiency, but will this be sufficient in the future? If we take a new look at this, we may perhaps find that in the long run it pays to record feed consumption in some way. For example, in performance testing young potential AI bulls for growth, feed consumption could be recorded exactly during a limited period (e.g. one to two months) at a reasonable cost. In this way, one could select rather efficiently for the trait itself. Improvements in the technique of measuring feed consumption would be very welcome. Is enough being done in this field?

Individual differences

It has been said that animal breeding is the science of averages. But it is the superior individuals that improve the population. This is especially true when it comes to utilization of gene resources from outside the domestic population. If we want to improve feed efficiency, a thorough screening for exceptional individuals might pay handsome dividends.

The study by Richardson et al. (1971), although based on limited numbers, indicates that there may be considerable differences in feed conversion between individuals (see Figure 2). It is interesting to note that the sire that ranked better on the all-forage diet than on the grain-and-forage diet came from New Zealand, where grain feeding is rare.

In general, we can note that as feed resources become scarce and concentrate feeding is practised to a smaller extent, breed and individual differences in feed conversion become more important.

Table 1 Information on some cattle breeds in Finland

¹ Including first and second generation crosses.
² Number of cows: Ayrshire 799, Finncattle 323, Friesian 343.
³ Number of bulls: Ayrshire 430, Finncattle 38, Friesian 50.
⁴ Mainly crossings.
⁵ Number of cows: Ayrshire 27 149, Finncattle 4 944, Friesian 3 005.
⁶ 0 = no mastitis to 4 = culled because of mastitis.

Fertility

Cunningham (1974) has noted that when selection for increased milk production is efficient in the domestic population, it probably does not pay to start importing genes unless the foreign population is at least 20 percent better genetically on an average. With regard to fertility, the situation is quite different, because probably little if any gain is made by selection in most populations (Maijala, 1974). Foreign breeds might therefore help to push the average up immediately if they are superior to one's own animals. Finnsheep have already been mentioned as an example of these possibilities.

In poultry, the previous enthusiasm over the good viability of the Fayoumi breed seems to have faded (FAO, 1973). But is it not possible that if the feeding regime and conditions change in the future — when poultry may well become “ scrap animals” again — the breed may once more come into demand? Are there other potentially useful but largely unknown breeds?

FIGURE 2. Performance of 13 Jersey sire dairy progeny groups (228 daughters) on two diets in the United States

In pigs, there is not as much to be gained from an increase in fertility as in sheep and cattle, but nevertheless it might be rewarding to study some of the highly prolific breeds of China. This should be done as soon as possible, as the number of breeds is decreasing rapidly (Epstein, 1974).

In cattle, even small improvements in fertility would be of great value. Our knowledge about the genetic quality of different breeds in this respect is rather poor. According to Johansson et al. (1974), there seem to be differences among breeds in twinning rate, but it is doubtful if these are large enough for practical utilization. Likewise, it is generally accepted that there are differences among breeds in stillbirth frequency (Van Dieten, 1963). These, as well as the variations in twinning rate, might most efficiently be utilized by selection and use of exceptional (progency tested) sires.

In Finland, Maijala (1974) has drawn attention to the clearly higher non-return rate (about 5 percent) of Finncattle compared to Ayrshires. At present very little attention is paid to differences of this kind in most countries, and an objective evaluation of breeds is seldom attempted.

Ninsiang sow from Hunan Province, China. (Photo courtesy of Commonwealth Agricultural Bureaux)

Finally, should we perhaps be a little more worried about genotype X environment interactions? It is possible that in the future our animals will be less well fed and cared for than they are today. In this event, breeds and animals remaining fertile under poor conditions may be in higher demand than at present.

Differences in disease resistance

Incorporating disease-resistant genes from foreign populations (if such genes can be found) theoretically offers enormous benefits. Most geneticists are, however, sceptical about the possibilities. Admittedly, vaccination and other veterinary measures seem to offer a cheaper and more efficient method. On the other hand, we should not forget that there are differences among poultry breeds in resistance to pullorum disease (Hutt, 1974) and that some breeds of cattle are trypanotolerant (Finelle, 1973). Especially with regard to the situation in the developing countries, one should not too hastily dismiss all attempts to breed disease-resistant animals. According to Rendel (1972), in Australia there are clear differences between bull progeny groups with respect to tick resistance.

And what about the mastitis problem? Many veterinarians have unsuccessfully attempted to overcome this by treating cows repeatedly with antibiotics. We know that there are genetic differences among animals in mastitis susceptibility (Hutt, 1974), but we still do not believe they can be utilized in practice. However, we are perhaps unduly pessimistic; according to a study (Lindström, unpublished), it seems that bulls could be progeny tested relatively easily by a simple field test (h² ≃ 10–15%, N = 23 200. See Table 1). Already with first and second calvers there seems to be a fairly large variation between sires.

Summary

In the developing countries there is a real need for the creation of new breeds. Elsewhere, development of new breeds should be undertaken only when substantial advantages seem likely. On the other hand, importation of limited gene samples is always an option which should be considered. A careful screening of foreign populations (neighbouring and exotic), combined with thorough evaluation, is recommended. In deciding what kinds of animals (genes) will be needed in the future, the possibilities and priorities in maintaining various species should be taken into account. Future developments in the techniques of egg transfer and sex control in sheep and cattle are likely to decrease the need for multipurpose animals. It seems probable that in all species feed efficiency and fertility traits will become increasingly important. Utilization of foreign breeds and exceptional individuals with these traits should therefore receive more attention. In the future a higher premium may be placed on animals better able to remain healthy and productive under poorer conditions than those of today. Breeding for disease resistance may one day be successful.

References

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