Abstract:
PRESIDENTIAL ADDRESS REPRODUCTIVE PERFORMANCE OF SHEEP IN AUSTRALIA R. H. WATSON* Summary Systematic study recent years. As more reproductive behaviour variable. Study of the of available knowledge of reproductive function of sheep has expanded information has become available it has become and performance in flocks throughout Australia is mechanisms controlling reproductive function and by producers need to take account of this great rapidly in clear that extremely application variability. Identification of ewes which mate and of returns to service, weighing at intervals of a small number of ewes in the flock, and picking up and counting of dead lambs-all simple to undertake - would provide information allowing definition of sources of wastage in reproduction on individual properties without delay, and it is in every producer' interest that he should include them in his programme. s However full attainment of potential performance will be hindered until field services to help individual producers with their problems are still further expanded and much more information is available on the factors which determine reproductive function in the widely varied field situations that exist. Rate of improvement in the reproductive performance of the national flock is likely to depend largely on the rate of movement of the 'centre of gravity' of the sheep industry from the pastoral areas to more highly developed areas, and on demonstration of the advantages of either producing more lambs annually or producing the required annual number of lambs from fewer ewes. 1. INTRODUCTION Our Society is concerned with all forms of animal production in Australia. This address is confined to reproductive performance in sheep, one aspect of production and one species of animal only. It is hoped that those who are not interested in this subject per se may still gain something from a critical analysis for one situation of features which play some part in determining present level of and rate of improvement in performance in most aspects of commercial animal production. Comparison of mean annual performance during the last 15 years ( 19491963) with that during the first 15 years for which records for all s*tates are available ( 1926-1940) provides clear evidence of improvement in reproductive performance in the national flock (Table 1) . Relative to the number of ewes joined for mating, the mean annual proportion of lambs marked increased from *S. S . Cameron Animal Research Laboratory, Department of Agriculture, Werribee, Victoria. 1 TABLE 1 Change in reproductive performlance during the period for which records are available* 63.3 % in the earlier period to 69.9 % in the later period (ratio later: earlier 1: 10). In addition, the mean number of ewes joined annually increased by 25% so that the mean number of lambs marked increased by 38 % . However, the improvement in performance and the increase in the number of ewes joined for mating was by no means uniform in all States. At the one extreme a small improvement in the marking percentage in Queensland was accompanied by a decline in the number of ewes joined for mating, so that there was a mean decline of 7% in the number of lambs marked annually. At the other extreme, a substantial improvement in the marking percentage in South Australia was accompanied by an even greater increase in the number of ewes joined, and the mean number of lambs marked annually increased by 110%. The 'centre of gravity ' of the sheep industry has been moving from the pastoral areas to the wheat, sheep and high rainfall zone with change in type of pasture as well as better control over nutrition. Breed structure and flock size has also been changing, and changes unknown to the author may have occurred too in the method of recording the statistics. All these features, as well as improvement in the standard of husbandry, may have contributed to the apparent improvement in reproductive performance. Whatever the origin of the improvement, present levels of performance leave little ground for complacency. II. DEVELOPMENT OF SYSTEMATIC STUDY OF REPRODUCTIVE PERFORMANCE Systematic study of reproductive function in sheep in Australia began in 19351940 with the work of Gunn on semen production in the ram and Kelley 2 on the sexual season in the ewe. It was quickly followed by the work of Underwood and his colleagues on the sexual season of the ewe in Western Australia, and on some aspects of nutrition in relation to reproductive performance. In the next decade, particularly in the years after the 1939-l 945 war, work was extended to other features of performance : the effect of presence of rams on sexual activity in ewes; the problem of infertility among sheep grazing pastures which consisted predom,inantly of subterranean clover; seasonal variation in a number of features of reproductive function in addition to occurrence of oestrus; neonatal mortality among lambs. Workers at quite a number bf centres became involved in these studies, but they were few enough still to list by name: Bennetts as well as Underwood and his colleagues in W.A.; Riches, Kennedy, Barratt and Hayman at C.S.I.R.O. Field Stations; Watson, Alexander and Radford, C.S.I.R.O. Melbourne; Morley at Trangie in N.S.W.; Moule in Queensland. Rapid expansion of the work occurred during the following decade with renewed activity at the University of Sydney, and initiation of work at the University of New England and the Ian Clunies Ross Laboratory C.S.I.R.O. on a major scale, and at many field stations of the State Departments of Agriculture on a lesser scale. This rapid expansion of activity has continued into the present decade. Some idea of the magnitude of the increase in activity in recent years is provided by the contributions to our Biennial Conferences. Contributions on reproduction in sheep increased from 3-8 at the first four Conferences to 20-21 at the 5th and 6th Conferences. Initially there was a tendency, perhaps inevitable, to generalise from the little information that became available, and to extrapolate from laboratory or well controlled field station conditions to the varied environments within commercial flocks. There was a tendency to consider, for example, that ewes would not mate if joined in the spring, that ewes running continuously with rams behaved like ewes that had been separated from rams, that variation in duration of daylight was the sole factor controlling the seasonal variation in sexual activity in ewes, that better reproductive performance was associated with mating in autumn than with mating in spring, that most neonatal mortality was of much the same type and so forth. As more information has become available, it has become clear that reproductive behaviour and performance in flocks throughout Australia is extremely variable and rarely if ever fits any such generalisations. Study of the mechanisms controlling reproductive function needs to take account of this great variability. III. FEAnTURES OF THE CURRESNT STATE OF KNOWLEDGE Most of the pertinent literature is listed by Watson ( 1962). Source o f information will be cited here only to papers not included in that review. (a) Factors aflecting reproductive function In contrast to the situation with dairy cattle, effects of infectious diseases on reproduction in sheep would appear at present to be of lesser importance than 3 those of other factors. These other factors include light, temperature, quality and quantity of nutrition, plant hormones and stress (Braden and Moule 1964), each of which have been shown under well controlled conditions to have an effect on reproductive function in the ewe. Light, temperature and nutrition also affect reproductive function in the ram although the mode of action does not always follow the same pathways as in the ewe. The seasonal variation in the physical and nutritional environment is accompanied by seasonal variation in a variet y of features of reproductive function, the most important of which are perhaps incidence of oes,trus and occurrence of multiple ovulation in the ewe and semen production in the ram. In recent years it has become clear that the effect of the various environmental factors is mediated by neural as well as humoral mechanisms (Radford 1966), but the nature of the neural mechanisms is perhaps even less defined than the humoral mechanisms. The magnitude and the ductive function vary widely and even properties within great degree of precision for time relationships of the seasonal variation in reprobetween years, breeds and strains of sheep, districts districts. They still cannot be predicted with an y any otne situation. Analysis of the factors operati ng in any one field situation is hindered both bY paucity of informatio,n on the precise nature and time relationships of the seasonal variation in flocks in any one locality, and by lack of direct information on the combined effect of the different factors. Since we may not yet know all the factors which may influence reproductive function, it is difficult to see how effective progress can be achieved without study in depth within the particular environment in which the nature and time relationships of the seasonal variation is defined. This still remains to be undertaken. Until it is undertaken we are unlikely to know why the incidence of twins is much higher in some years than others, why the onset of the sexual season is earlier in some years than others, and why many ewes may fail to lamb in some years and few in others. Perhaps some of these features may be controlled by o,ther means, before we have the answers to these questions. (b) Heritability in relation to! reproductive performance There is wide variation between breeds in the frequency of multiple births. Within breeds, selection for twinning has led to progressive improvement in performance (Turner et al. 1962). On the other hand selection for wool production may have introduced genetic factors adverse to reproduction. This is suggested by the inverse relationship between face cover and fertility and between skin fold and fertility (Dun 1964) observed in the flock at Trangie. A difference has been observed between two neighbouring flocks in Western Victoria in the incidence of perinatal mortality in lambs independent of any difference in birth weight (Watson and McLaughlin, unpublished data). From observations on the ewes and lambs from these two flocks under common conditions, it is difficult to avoid the conclusion that there is an inherent difference between the flocks in the ability of the newborn lambs to cope with cold wet and windy weather conditions. Difference between flocks such as these observed at Trangie and those currently being studied in Western Victoria provide material for study of the physiological bases of differences in performance. Such studies are indeed being pursued both with the Trangie and the Victorian material. It may be remarked that in each instance the opportunity depended on adequate definition of the field situation. Indeed it is not yet certain that there has been adequate definition of the field situation in the Victorian studies. (c) Hormonal control of oestrus Attempts at control of reproductive processes by treatment with hormones have had a rather disappointing history, perhaps as a consequence of an ad hoc approach in a situation insufficiently understood. Study of the physiology of the oestrous cycle by the group based on the University of Sydney has now been used to define the requirements for practical control of oestrus and ovulation. Study of these requirements has led to successful development of a practical method of control (Robinson 1964). The place of this new technique in sheep husbandry has still to be determined, and it may be some time before its potentialities are fully assessed. (d) Wastage in reproduction Reproductive performance is determined, on the one hand, by the wastage associated with failure to mate, return to service, failure to lamb and mortality among lambs and, on the other hand, by the number of multiple births. Both the observed wastage and the incidence of multiple births have been extremely variable in neighbouring flocks in the one area as well as in flocks in different areas. Observations on the incidence of wastage of various types define the sources of loss but do not provide information as to cause. Why in some flocks do a high proportion of ewes return to service or fail to lamb? Why in some flocks do a high proportion of lambs die without ever obtaining a drink? Answers to questions such as these are only likely to be obtained by studies in depth in flocks in which the high incidence of loss has been defined. Effective studies of this nature will require good producer co-operation, a great deal of ingenuit y in design, a really critical approach, and adequate facilities on the spot. All can be achieved. IV. APPLICATION OF AVAILABLE KNOWLEDGE The systematic study of reproduction in sheep during the las,t 30 years, then, has indicated many factors which may affect reproductive performance of sheep in the field. Attention is already given to some of these factors in current husbandry practice. No control over others, such as nutrition or ambient temperature, may be practicable in some areas. It is control over the remainder that offers opportunity of improvement in reproductive performance. In many instances unfortunately, neither the precise means of application of knowledge in regard to a particular factor nor the gain in reproductive perform5 ante that may be expected by its control can be stated. Nutrition in late pregnancy may be cited as an example. Poor nutrition at this time is certainl y accompanied by high neontal loss of lambs. This has been known for lo-20 years or more. However, it is still not known what the level of nutrition should be, and how it may be achieved. There has been little improvement in performance in many instances where feeding has been undertaken in later pregnancy. Perhaps, it could not have been expected had the situation been adequately analysed, but is present information sufficient to allow adequate analysis? Improvement in performance at the national level depends ultimately on improvement on the individual property. The greatest difficulty of improvement in performance on the individual property is lack of knowledge as to where losses in performance are occurring. The only figure immediately available, generally, is the number of lambs marked and it may be the next lambing season before more information can be gained. Interest tends to be diverted to other more pressing problems during the interval and remain diverted subsequently. Information allowing more immediate definition of the problem is needed to preverrt this diversion of interest elsewhere. Picking up and counting dead lambs, identification of ewes which mate and of returns to service, and weighing at intervals of a small number of ewes in the flock would provide the sort of information needed. All are simple to undertake and it is in every producer 's interest that he should include them in his programme. V. MEANS OF ACHIEVING THE FURTHER KNOWLEDGE NEEDED Understanding of the fundamental physiology of reproductive function is only likely to be achieved under the well controlled conditions of the laboratory. Understanding of reproductive performance in sheep in the field, on the other hand, is only likely to be achieved when the nature and variation of reproductive function in the field situation is defined. Only when the situation in the field is adequately defined is it possible to decide whether the features of function being studied in the laboratory include or are even pertinent to it. There is scarcely a situation in the field that is adequately defined for this purpose. Field study of the type envisaged requires the same curiosity, the same initiative, the same critical approach and the same training in research as laboratory study. It requires equal if not greater ingenuity in devising techniques which will help to offset the uncontrollable variability within any field situation. It is long range work requiring great patience. In certain circumstances, it involves some degree of isolation from one's colleagues. The people that meet these requirements are rare gems and are to be encouraged in every way to continue to remain in field research. It has sometimes been claimed that the well controlled conditions laboratory provide a more effective means of obtaining the information needed than the less well controlled conditions in the field. It cannot be sised too strongly that the two do not study the same situation. Both are 6 of the that is emphaneeded for progress, if progress is taken to mean providing the knowledge whereby efficiency and volume of production may be improved. They are complementar y not competitive. VI. INCENTIVE TO IMPROVE REPRODUCTIVE PERFORMANCE Two situations needed to be considered, (i) more lambs from the same number of ewes and (ii) the same number of lambs from fewer ones. (i) Improvement in reproductive performance represented by more lambs from the same number of ewes must lead <to an increase in the gross returns if the extra sheep can be sold. It may also lead to an increase in the gross return through greater wool production as a consequence of more intensive culling of poor producers. However the increased returns will be offset by costs involved in improving the performance; perhaps costs of identifying ewes which mate, of supplying more feed in late pregnancy, of more intensive care at lambing and so forth, as well as slightly lower wool production and slightly higher animal mortality in the breeding flock. Watson ( 1962) argued that there might be some doubt whether the returns would offset costs unless it was clear that there would be a ready market for the extra. sheep. Is there such a market? It may be expected that, for some time to come at least, there will be a continued annual need for extra sheep to meet demands of pasture development, more intensive husbandry and flocks depleted by drought. There should also be a gradually increasing need for sheep to supply meat in Australia. There is too, of course, an immense need for meat by the world's rapidly growing population outside Australia. On the other hand, in the absence of drought, present levels of performance are allowing a steady increase in sheep numbers (5 million in 1964) and price of sheep does not seem to have even kept pace with change in the value of money (B.A.E. Australia 1957, 1962, 1965). Price of sheep in the B.A.E. surveys, certainly, does not suggest that demand is outpacing supply, and it does not suggest economic return as an y general incentive to produce more lambs. (ii) Improvement in reproductive performance represented by the same number of lambs from fewer ewes provides capacity for some increase in gross returns by allowing more dry sheep to be run as wool producers. In addition it may lead to decreased costs of production in a variety of ways: fewer rams to be provided, paddocked and fed; less feed for ewes where feeding is necessary in late pregnancy; fewer ewes to be supervised at lambing; but those too may be offset by increased costs of attaining the improved performance such as those mentioned in the previous paragraph. However, incentive to improve performance to obtain the same number of lambs from fewer ewes is only likely to be fully effective when present uncertainty as to the magnitude of the likely effect of these various features on returns is replaced by factual information. VII. THE FUTURE Irrespective of any special efforts that may be made, improvement in the national level of reproductive performance is to be expected as an outcome of the progressive movement of the 'centre of gravity' of the sheep industry from the pastoral areas to more highly developed areas. The current trend to increase in rate of stocking, too, may be accompanied by change in reproductive performance, but the nature or magnitude of the likely change is not clear. While on the one hand, high rates of stocking would be expected to lead to some decline in level of performance, graziers may not be prepared generally to accept such high rates of stocking. On the other hand, improvement in management which is likely to accompany increase in rate of stocking may offset any effect on reproductive performance of increase in rate of stocking per se particularly where current performance is already low. There is a considerable body of information available which can be applied immediately towards improvement in performance on individual properties where sources of loss in performance have been defined. Simple means are available whereby sources of loss may be defined in many situations. These, together with the increase in attention to problems of individual producers that the current growth in consultant services allows, must lead to some improvement in performance. All too frequently still, however, present consultant services cope with individual problems and, where they are able to do so, whether the effort suggested in solution of the problem encountered by appropriate increase in performance, or indeed difficulty in solution at all. are unable to there is doubt will be repaid suggesting any Full attainment of potential performance will be hindered until field services to help individual producers with their problems are still further expanded and much more information is available on the factors which determine reproductive function in the widely varied field situations that exist, and the mechanisms whereby they do so. This information is only likely to be gained by further study in both field and laboratory. It will require research workers of high skill and training to take and maintain interest in field problems, if a balance between field and laboratory study is to be maintained. Even where adequate information is available, improvement in performance will require effort on the part of the producer. Concerted effort in this regard seems unlikely at present when so much can be achieved m.ore certainly by efforts in other directions such as increase in rate of stocking. Nevertheless, efforts of, and results attained by, occasional producers may be expected to stimulate interest of increasing numbers as time goes on. I have only to cite as an example the interest created in Victoria by Mr. A. R. Beggs' success in improving the performance in his flock (Beggs and Campion 1966). These various. considerations leave little doubt that there will be continued improvement in the national level of reproductive performance. However, the rate of improvement will depend largely on the rate of movement of the centre of gravity of the sheep industry from the pastoral areas to more highly developed areas, and on demonstration of the advantages of either producing more lambs annually or producing the required annual number of lambs from fewer ewes. 8 VIII. CONCLUDING REMARKS At the outset it was remarked that those not interested in reproductive performance of sheep per se might be interested in this address as a critical analysis for one situation of features which play some' part in determining present level of and rate of improvement in performance in other aspects of commercial animal production. Perhaps in this regard it may be useful to recapitulate and state briefly those features discussed that need to be appreciated in analysis of possibilities of improvement in other aspects of animal production. 1. Course of development of systematic study within the particular area of production. 2. Current state of knowledge. 3. Precise means of application of knowledge in regard to each particular factor along with the gain that may be expected from its application. 4. Means of achieving the further knowledge required; and among these, field study ranks equally with laboratory study - not merely operational research but research into the biology of the field situation. 5. Incentive to improve performance. 6. Services needed to assist improvement in performance. VIII. REFERENCES B EGGS , A. R., and CAMPION, E. J. ( 1966). Field techniques to increase lamb survival and flock fertility. Proceedings Australian Society of Animal Production 6: 169. CONOMICS BUREAU OF AGRICULTURAL E Survey 1954 (Canberra). REAU OF , AUSTRALIA ( 195' The Australian Sheep Zndustry 7). A GRICULTURAL , ECIONOMICS, A USTRALIA ( 196 Sheep and Wool Industry. Third Ed ition (Canberra). USTRALIA 1). Statistical Handbook of the BUREAU OF A GRICULTURAL E CONOMICS , A Survey 1957- 1960 (Canberra). ( 1962). The Australian Sheep Zndustry Supplement to the Statistical .EAU OF A GRICULTURAL . E CONOMICS , AUSTRALIA ( 1964 Handbook of the Sheep & Wool Industry (Canberra). B UREAU OF A GRICULTURAL E CONOMICS , A Survey 1960- 1963 (Canberra). USTRALIA (1965). The A ustralian Sheep Zndustry BRADEN, A. W. H., and MOULE, G. R. (1964). Effects of stress on ovarian morphology and oestrous cycles in ewes. Australian Journal of Agricultural Research 15: 937. D UN , R. B. (1964). Skin folds and Merino breeding. I. The net reproductive rates of flocks selected for and against skin folds. Australian Journal of Experimental Agriculture and Animal Husbandry 4: 376. A ustralian Society of Animal Production 6: 19. R ADFORD, H. M . (1966 ). Regulation of the breeding season in mammals. Proceedings of the R OBINSON , T. J. ( 1964). Synchronization of oestrus in sheep by intravaginal and subcutaneous application of progestin impregnated sponges. Proceedings of the Australian Society o f Animal Production 5: 47. T , H. N., HAYMAN, R. H., T RIFFITT , L. K., and P RUNS TER, R. W. (1962 ) . Response to selection for multiple births in the Australian Merino. A nimal Production 4 : 165. W ATSON , R. H. (1962). Reproduction in sheep. The Simple Fleece (Melbourne University Press) pp. 67-81. UR NER 9