Tuatara: Volume 1, Issue 2, May 1948
Biological Aspects of Animal Research in New Zealand
Biological Aspects of Animal Research in New Zealand
The term animal research as it is generally understood in New Zealand and as it is used in this article has, of course, a limited application. It is confined to investigations designed to increase the efficiency of the production of substances of animal origin which are required for human use. Though limited in their scope these investigations do deal with biological problems and the title of this article might equally well have been worded: “Animal industry aspects of biological research in New Zealand.” All aspects of animal research should be of interest to biologists and it will be the object of this article to increase that interest and perhaps to increase the number of biologists who manifest that interest, for if biologists are to participate effectively in animal research they must first be interested in animal research.
The national economy of New Zealand is based very largely on its animal products which provide over 90% of the total exports, so that there are good economic and social reasons for studying the problems of animal production. What are these problems? Broadly, one may say that they fall naturally into two classes—problems of heredity and problems of environment.
The art of animal breeding is very much older than the science of genetics, and even today the geneticist cannot help the animal breeder nearly as much as he can the breeder of plants. But fortunately the contribution of the geneticist is steadily increasing. In many spheres progress in animal breeding has almost stopped and further advances will depend on the application of the principles of genetics. Let us look at a few cases. The most important meat animal in New Zealand is the lamb. Now meat consists largely of muscle and fat, two tissues which develop relatively late in most animals. To produce an attractive fat lamb it is necessary that these tissues should develop earlier than usual. Fortunately the characters responsible for early maturity in the Southdown sheep are so dominant that a Southdown ram may be crossed with a ewe of any breed and the lamb will mature early provided it receives adequate milk from the ewe. The Romney Marsh ewe nearly always does provide enough milk for one lamb and generally enough for two. Consequently New Zealand lamb is famous for its quality. But there still remains a major problem for the geneticist. The New Zealand fat lamb breeder seldom produces more than 100% of fat lambs from his ewes. Using a different breed in Englandpage 4
150% has been achieved. The breed used in England would probably not suit New Zealand conditions, but we badly need that extra 50% of lambs to help consume the spring and summer flush of grass much of which at present, is often wasted. Twinning in sheep is not very strongly inherited; it may be a recessive character. It needs to be bred for in the Romney Marsh without reducing milk and wool production–a nice problem in animal genetics.
An even more baffling problem faces the breeder of dairy cattle. Many dairy farmers derive their income almost entirely from the sale of butterfat. They therefore desire cows which will produce large volumes of milk with a high concentration of butterfat, characters which are inherited separately. The inheritance of high production of milk appears to be very complex. Moreover, this character does not find expression in cows until they are two years old and it remains completely dormant in bulls. No method has been devised for assessing the genotype of bulls for butterfat production based on examination of their phenotype, and the position in regard to cows is very little better. In such cases it is necessary to resort to the practice of sire surveying in which a bull's genotype is measured from the production of his first group of daughters. Though reasonably effective this method is very cumbersome and slow and it seldom reveals a bull's worth before more than half of his breeding life is passed. However, the consistent uses of the best progeny tested sires in stud herds by means of artificial insemination should result in a gradual concentration of the desirable genes. Concurrent with this practice should go an intensive search for measurable manifestations in the bull of those genes which at present can only be estimated after they have been transmitted to his daughters. To this end a study is being made of some thirty erythrocyte antigens which are inherited as simple dominants. Should the genes for any of these reside on the same chromosomes as genes responsible for high butterfat production, it might become possible to assay the productive potentialities of both bulls and heifers at an early age. American workers have suggested that a heifer's capacity for lactation may be assessed from the degree of development of mammary tissue which occurs at an early age. This would be extremely valuable as it would save feed at present wasted on low producers during the first two years of their lives.
Occasionally an undesirable character is found and it is necessary to determine its mode of inheritance so that it may be eliminated. An interesting example is a photosensitivity which occurs in some Southdown sheep. This has been shown to be due to phyloerythrin, a porphyrin into which chlorophyll is changed in the alimentary tract of ruminants. Normally this is excreted in the bile. In the affected animals there is a liver dysfunction which allows the phyloerythrin to be absorbed into the circulation and enough reaches the skin to render page 5 it unduly sensitive to light. Breeding experiments have shown that the condition is inherited as a simple recessive.
One could go on multiplying examples but perhaps enough has been said to indicate that the geneticist has ample scope in the realm of animal research.
To obtain the optimum production from well bred animals they must be provided with an environment in which they can give full expression to their heritage. In fact, so complementary are the effects of heredity and environment that it is often very difficult to assay them separately.
Of all the factors in an animal's environment food is much the most important. The expanding science of animal nutrition is now so vast that scientists are devoting their lives to the study of single phases. The climate of New Zealand is so favourable to pasture growth during almost the whole year that our animal industry has been based on the grazing animal. Much work is required to provide a proper understanding of the nutritive properties of the growing plants upon which animals graze and the factors upon which those properties depend. The composition of plant tissue is known to be affected, for example, by species of plants, by soil composition, by climate, by stage of growth and by rapidity of growth. So complex are these factors that often they can be measured only in terms of the response of the animals grazing them.
Experimentation with grazing animals is a recent development and adequate techniques have yet to be devised. Animals are notoriously variable and it is often difficult to provide similar homogenous groups with which to measure the effects of the treatments under test. The use of identical twins seems likely to be of great assistance in this regard.
Difficulties are encountered in measuring the amount of pasture eaten, in adjusting the intake to a particular level and in accurately sampling what is eaten. Moreover, pasture never remains static either in quantity or quality and the cumulative effect of such variations on the metabolism of the animal may be very important. For example, the same total amount of food may be fed to two pigs over a period of six months and their final weights may be the same, but their conformations and the ratios of their tissues may be entirely different. Generous feeding followed by a restricted diet produces a long lean pig with a relatively high proportion of bone and muscle while the reverse procedure results in an excessively fat pig. Or again, serious ketosis and death ensue in ewes when they receive an ample diet early and are starved late in the gestation period. The same total amount of food will maintain them in perfect health if the reverse procedure is adopted.
Environmental factors may result in pasture plants acquiring dangerous properties. They may, for example, develop cyanogenetic gluco- page 6 sides, nitrates in toxic properties, photosensitising agents, liver toxins or even oestrogenic hormones in quantities sufficient to derange the structure and functions of reproductive organs.
Space does not permit more than mention of some of the other important environmental factors. The direct effect of climate can be very important. For example, high temperatures or sudden changes in temperatures may seriously interfere with spermatogensis in rams. Then there is the host of living organisms which are such important environmental factors. Insects, trematodes, cestodes, nematodes, protoza, bacteria and viruses may cause a wide variety of diseases. On the other hand the rumen micro-flora are capable of digesting cellulose and synthesising amino acids and vitamins for the use of their hosts.
The grazing animal spends its whole life in the closest contact with the other living organisms which share its environment. If left undisturbed a state of flexible equilibrium is reached in which the number of each species is adjusted so that its requirements may be met. Man often unconsciously upsets this balance sometimes with disastrous results. It is the object of the animal research worker to show how the balance may be adjusted to provide optimum conditions for domesticated animals to produce those substances which contribute so largely to the health and comfort of mankind. It is hoped that this brief article may stimulate at least a few biologists to interest themselves in this important department of their great science.