Studies on growth and variation in large animals

Abstract

The hopes which accompanied the birth and infancy of the science of genetics have somewhat faded. Expectations based on the early Mendelian experiments that animal breeding would be revolutionized and progress accelerated proved ill- founded when applied to economic characters with a complex mode of inheritance. Time and effort have since shown that a complete genetic analysis of most of these qualities is hardly possible and perhaps not even desirable. The animal geneticist is therefore obliged to think in terms of gene combinations rather than of genes, and to abandon attempts at factorial analysis.This change of thought model with its associated statistical techniques does not bring the immediate problem of genetic research with domestic animals any nearer a solution. shat problem is the recognition, measurement and exploitation of genetic variation. It is the old problem of relating phenotype to genotype but expanded into the more general question of the interaction of genes not only with external environment, but also with the internal environment set up by the activities of other genes.As a purely genetic problem this would be exceedingly involved, but it is rendered still more difficult by the power of environment to produce variations indistinguishable from those arising from gene differences. The search for these differences therefore requires a simultaneous study of the effects of environment with the object of discriminating between the two types of variation. It would obviously be of great advantage if either genetic constitution or environment could be kept constant, and attempts to do this are frequently made. Even if these attempts did not usually demand more time and expense than most workers can provide, they would, if successful, still leave unsolved the very important problem of the interaction of heredity and environment in the practical breeding of animals in which neither is constant. As an example the variation in the milk production of sows may be cited. Here it is clearly of moment to identify those animals which are genetically superior not so much under standard conditions as under the changing conditions of humidity, temperature, housing and feeding characteristic of most piggeries.The following pages contain some of the results secured so far in an attempt to assist in the solution of the general problem of the geneticist dealing with domestic animals. Most of the material has been obtained from the pigs of the Institute of Animal Genetics in Edinburgh, but as the field of research is not peculiar to the pig, opportunities for advancing the work with material from other sources have been gladly taken.Three major subdivisions of the studies may be recognized. The first is concerned with the search for sources of variation in birth weights, a subject which derives its interest from its bearing on the survival and growth of the new -born. Breeding experiments with pigs have still to be completed, but an effort to alter birth weight by raising the plane of nutrition of the sows is described. l'aturally occurring variation in the birth weights of sheep and of humans has been studied with extensive material suitable for examining the influence of environmental factors.The second subdivision includes the results of research into the growth of pigs and sheep from birth to weaning, that is, during the time when the milk production of their dams is of special significance. nere also the object has been to measure variation and to determine what proportion of it may be attributed to heredity.The third subdivision contains accounts of investigations into the post- weaning growth of pigs. During their progress toward bacon weight, pigs trace out growth curves which vary not only from litter to litter but also from one litter -mate to another. These inequalities of performance provide the raw material for selection aiming at the ideals of early maturity and ever more rapid growth. But before they can be confidently used for that purpose, they must be described in terms of heritable characters. Thus the efficient planning and conduct of breeding programmes no less than the practical application of Testing Station results, depends upon the definition and measurement of genetic differences in growth rate. +'iith this in mind, an extensive study has been made of the variation found in a single herd with a standard system of management. Further, recent developments have suggested that growth rate has an important bearing on the body proportions of the marketed animal, so that it has been of interest to compare the observed differences in growth rate with the corresponding variations in carcass quality.Owing to the nature of the materials, the various phases of the attack on these problems have not been completed in the order in which they were conceived. In several instances the results of breeding experiments which would provide valuable complementary data are not yet available. It is hoped, however, that what has been learnt of variation in these studies will aid the interpretation and enhance the value of the finished work.1. THE GROWTH -RATE OF LAMBS IN CANTERBURY. A PRELIMINARY STUDY OF THE VARIATION IN THE GROWTH -RATE OF LAMBS IN CANTERBURY. BY H. P. DONALD, Extracted from the New Zealand Journal of Science and Technology, Vol. XVII, No. 3, pp. 497 -519, 1935. || 2. THE MILK CONSUMPTION AND GROWTH OF SUCKLING PIGS H. P. DONALD. Reprinted from THE EMPIRE JOURNAL OF EXPERIMENTAL AGRICULTURE Vol. V. No. 20. October 1937 || 3. THE MILK CONSUMPTION AND GROWTH OF SUCKLING PIGS. By H. P. DONALD. Reprinted from THE EMPIRE JOURNAL OF EXPERIMENTAL AGRICULTURE Vol. V. No. 20. October 1937 || 4. SUCKLING AND SUCKLING PREFERENCE IN PIGS. By H. P. DONALD. Reprinted from THE EMPIRE JOURNAL OF EXPERIMENTAL AGRICULTURE Vol. V. No. 20. October 1937 || 5. THE RELATIVE IMPORTANCE OF SOW AND LITTER DURING THE GROWTH OF SUCKLING PIGS: A COMPARISON OF FOSTERED WITH NORMALLY REARED PIGS. By H. P. DONALD. Reprinted from THE EMPIRE JOURNAL OF EXPERIMENTAL AGRICULTURE Vol. VII. No. 25. January 1939 || 6. THE EFFECT OF PRENATAL WEIGHT- CHANGES IN BREEDING SOWS ON THE NUMBER AND SIZE OF NEW -BORN PIGS. By H. P. DONALD AND I. FLEMING. Reprinted from THE EMPIRE JOURNAL OF EXPERIMENTAL AGRICULTURE Vol. VI. No. 24. November 1938 || 7. Sources of Variation in Human Birth Weights By H. P. Donald. REPRINT FROM THE PROCEEDINGS OF THE ROYAL SOCIETY OF EDINBURGH SESSION 193$ -1939 VOL. LIX -PART I -(No. 9) 8. WEANING WEIGHT OF PIGS AND LITTER SAMPLING WITH REFERENCE TO LITTER SIZE BY A. D. BUCHANAN SMITH AND H. P. DONALD. FROM THE JOURNAL OF AGRICULTURAL SCIENCE VOLUME XXVII, PART IV. OCTOBER 1937 || 9. ANALYSIS OF POST -WEANING GROWTH IN PIGS BY A. D. BUCHANAN SMITH AND H. P. DONALD FROM THE JOURNAL OF AGRICULTURAL SCIENCE VOLUME XXIX, PART II, APRIL 1939 || 10. INFLUENCE OF AGE AND WEIGHT OF PIGS ON RESPONSE TO SODIUM EVIPAN H. P. DONALD AND J. RAVENTÓS. Reprinted from THE JOURNAL OP PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 65, No. 4, April, 1939 || 11. THE VARIATION IN LENGTH OF INTESTINE IN NEWLY HATCHED CHICKS. By H.P.DONALD || 12. GROWTH RATE AND CARCASS QUALITY IN BACON PIGS. By H.P.DONALD || 13. GROWTH RATE AND CARCASS QUALITY IN BACON PIGS A STUDY OF POLYNOMIAL COEFFICIENTS FITTED TO GROWTH RATE DATA BY H. P. DONALD. 'Reprinted from the Journal of Agricultural Science, Vol. XXX. Part IV ||