Abstract:
REPRODUCTIVE PERFORMANCE OF SHEEP IN VICTORIA R. H. WATSON* I. INTRODUCTION Reproductive performance in Victoria is discussed in this paper in relation to breed structure, and to level of nutrition as reflected in pasture improvement, conserved fodder, -droughts and wool production per animal. Where not otherwise stated, the statistics discussed have been extracted from the Victorian Government Statist' records. s II. BREED STRUCTURE (a) The State flock The Victorian flock includes sheep of most British breeds as well as Merino, Corriedale, Polwarth, Merino comeback and crossbred sheep. The proportion of Merinos in the flock declined from 39% in 1935 to 32%. in 1947 after which it increased progressively to 44% in 1962 (Table 1). Along with the increase in the proportion of Merino sheep in the flock since 1947, there was a decline in *Animal Husbandry Research Centre, Department of Agriculture, Werribee, Victoria. 123 the proportion of British breed rams in the ram flock from 53 % in 1947 to 40% in 1953, but it then increased again to 47 % in 1962. (b) District variation Of the sheep in each County in 1962 the proportion that were Merin o ranged from nil to 79%. In like fashion the proportion of British breed rams i n the ram flock ranged from 9 to 96% (Figure 3). (c) Relation to type ,of enterprise Merino, Corriedale and Polwarth rams have been most commonly used as sires where wool production has been primary object of the enterprise, and British breed rams where the primary object has been fat lamb production (B.A.E. Australia 1957). Ewes of all breeds have been used as fat lamb mothers, but in general crossbred ewes have been favoured for this purpose and Merino, Polwarth, and Corriedale ewes for breeding flock replacements in wool production (B.A.E. Australia 1957). III. LEVEL OF NUTRITION (a) Pasture im.provement and fodder conservation Since 1946, the annual increases in the area of improved pasture. amount of fertiliser applied to pasture, and the area of pasture cut for hay have all been 2l/2-5 times those previously (Figure 1). The total quantity in each instance in 1962 was at least three times that in 1946. On the other hand, the numbers of cattle and sheep increased only 1.7 and 1.9 times respectively during this period. It is to be inferred that during years of equivalent effective rainfall both G) total feed supplies and fodder conserved to offset seasonal feed shortages and those accompanying drought, and (ii) level of nutrition per animal must have been higher since 1946 than before that year. There is no reason to believe tha t effective rainfall has been less since than before 1946. Rainfall has certainly been above average in most years since 1946. (b) Periods of nutritional stress State-wide droughts in 1927, 1930, 1933 and particularly 1945 are described by Foley (1957). These were clearly years of serious feed shortage through the whole state. It is not simple to derive the feed situation from rainfall statistics in other years. However, the relatively low level of wool production per animal in the 1936, 1938, 1940, 1943 and 1944 seasons (Figure 2) indicates that these also were years of feed shortage. Similarly decline in wool production per animal in the 1948, 1953 and 1957 seasons suggests a decline in feed conditions, although the level of wool production was high relative to earlier years. IV. REPRODUCTIVE PERFORMANCE (a) The State flock Relative to ewes mated the numbers of lambs marked* has varied from 68 to 93 % excluding the very severe drought year of 1945 when it declined to 49% (Figure 2). While there is little evidence of any general increase in the level of reproductive performance, the level prior to 1946 differs from that later in one '`The first time an accurate count is made of lambs is at marking, usually when lambs are two to six weeks old. At this time tails are cut short, ears are clipped with the owners registered mark, and in most cases ram lambs are castrated. Fig. 1. -Increase in numb,ers of cattle and sheep in relation to improvement in feed supplies as reflected in fodder conservation, pasture improvement and artificial fertiliser applied to pasture. Of the total artificial fertiliser, at least 94% each year was superphosphate. (Sources of information: Sheep numbers, B.A.E. Australia 1961; Cattle numbers, B.A.E. Australia, 1963; Others, Commonwealth Bureau of Census and Statistics, Victorian office). respect. Prior to 1946, wide fluctuations in performance occurred every two to three years. Less than 75% of lambs were marked in 1927, 1930, 1933, 1938 and 1941 to 1945, and 88-93% were marked in 1926, 1928 and 1932. Since 1946 these wide fluctuations in performance have been absent. Between 75 and 87% of lambs were marked each year. (b) Vm-&ion between districts Relative to ewes mated, the number of lambs marked varied from 73 to 101% in the different Victorian Counties in 1962 (Figure 3), with a similar range of performance in other years. Variation between Counties within Statistical Districts tended to be as great as variation between Statistical Districts? Highest performance occurred in the most southern Counties along the coast and ranges, and in the most northern Counties in the plain of the Murray River system. ++For statistical purposes Victoria is divided into eight Districts each made up of three to five Counties. 125 Fig. 2.Variation in reproductive performance and wool production per animal 1926 to 1962 as extracted from B.A.E. Australia (1961). Records of wool production have been set back one year to refer to the year in which the wool was grown. There is some disagreement between Commonwealth and State statistics on wool production prior to 1934, but this does not affect pattern of variation from year to year. (c) Relation to breed and type of enterprise B.A.E. Australia (1962) found that the mean marking percentages in the Merino wool growing flocks, the crossbred wool growing flocks and the fat lamb flocks, mostly crossbred, were approximately 74, 79 and 88 respectively in 1959, when 83% of lambs were marked in the State flock as a whole. In many of the Merino wool-growing flocks less than 60% of lambs were marked. As might be expected from these figures of B.A.E. Australia, the marking Percentage in the different Counties is directlw related to the nronortion of British Fig. 3.-Reproductive performance in the different Victorian Counties in 1962 in relation to breed structure of the County flock as calculated from information supplied by the Commonwealth Bureau of Census and Statistics, Victorian Office. Curves fitted by eye. 126 breed rams in the County ram flock, and inversely related to the proportion of Merino sheep in the whole County flock. Figure 3 depicts the nature of the relationship in each instance in 1962. While the trend was the same in other years for which this information is available, some variation in susceptibility of Counties to feed shortage with consequent variation in slope of the curves is likely. (d) Relation to wool production Variation in lambing results from year to year has followed a closely similar pattern to that in mean wool production per animal (Figure 2). Minor differences in trend such as those in 1940 and 1941 are consistent with a displacement of about six months in the date of lambing and shearing, and the relation of each to rainfall and consequent pasture growth in the particular years. V. DISCUSSION The low lambing results in 1927, 1930, 1933 and 1945 were associated with statewide below average rainfall during the previous spring, the summer and the autumn. Low lambing results in 1936,, 193 8 and 1944 and decline in lambing results in 1953 and 1957 were also associated with a low level or a decline in the level of nutrition as reflected in mean wool production per animal relative to other years. The tendency for peaks in reproductive performance to follow the pronounced troughs in performance that are associated with droughts was commented upon by Watson (1962). Several reasons were suggested for the occurrence of these peaks of performance. Whatever the real reason they were generally accompanied by a corresponding improvement in mean wool production per animal. The progress in pasture improvement, use of fertiliser and fodder conservation without equivalent increase in animal numbers leaves little doubt that generally more feed has been available since 1946 than earlier. That the animals have indeed taken advantage of the improved nutritional supply is indicated by the generally higher level of wool production per animal since 1946 relative to the level in the period 1930-1945. It is certainly unlikely that this increase in wool production was more than partly, if at all, genetic in origin, since the initial increase occurred so sharply following an equally sharp reduction in stock numbers, and the level remained so consistently high subsequently. Accordingly it must be concluded that absence of fluctuations in reproductive performance since 1946 has been associated with, if not a consequence of, an improved level of nutrition. With the increase in the proportion of Merino sheep and the decline in the proportion of rams of the British breeds from 1947 to 1953, some decline in reproductive performance might be expected. The situation between 1953 and 1962 is not so clear. The increase in the proportion of rams of the British breeds indicates some return to fat lamb production with its higher reproductive performance. On the other hand, the continued increase in the proportion of Merino sheep suggests some expansion of Merino wool growing with its lower reproductive . performance. Estimate of the magnitude of the likely changes in reproductive performance associated with these changes in breed structure and type of enterprise may be made both from the results obtained by B.A.E. Australia (1962) in its survey, and the information set out in Figure 3. On both bases, the decline in the per - centage of lambs marked in the earlier period is unlikely to have been greater than 2 units, and the change in the later period is unlikely to have been greater than t- 1 unit, providing a total decline in performance from 1947 to 1962 of not more than l-3 units. It is unlikely, too, that any greater changes in reproductive performance would have resulted from changes in breed structure and type of enterprise from 1926 to 1947, since, in the earliest records, breed structure did not differ greatly from that between 1947 and 1962. Changes in reproductive performance associated with changes in breed structure and type of enterprise may even be less than these estimates. Variation between districts in both the physical and the nutritional environment is con founded with variation in breed structure and type of enterprise in the statistics and survey results on which the estimates are based. The failure to separate out the effects of variation in environment is likely to have exaggerated the estimates, since types of enterprise associated with high and low reproductive performance tend to be concentrated in more favourable and less favourable environments respectively. Relative to ewes mated the proportion of lambs marked in the Merino wool growing flocks surveyed by B.A.E. Australia (1962) was much the same in Victoria as in the corresponding zones in South Australia and Western Australia (72-74%), and it was higher in these three states than in New South Wales (68%). On the other hand, in the fat lamb flocks, mostly crossbred, surveyed by B.A.E. Australia (1962), the proportion of lambs marked to ewes mated was higher in Victoria (88%) than in the corresponding zones in the other mainland states. (74~85%), although lower than in Tasmania (101%). The relative contribution of breed, management and district environment to the difference in reproductive performance between Merino wool growing and fat lamb flocks is not clear. However, it is clear that lamb losses must have been high or many ewes must have failed to lamb in the Merino wool growing flocks in Victoria. Wastage from both of these sources was observed by Watson (1957) and Hyland (1960). In the fat lamb flocks on the other hand, wastage from these sources must have been low or there must have been a substantial incidence of twins. It is to be inferred that improvement in reproductive performance in Merino wool growing flocks in Victoria may still be achieved without any increase in the incidence of twin births, whereas in the fat lamb flocks improvement will be dependent on the rearing of more twin lambs. VI. REFERENCES B.A.E. Australia (1957). The Australian Sheep Industry Survey, 1954. Bureau of Agricultural Economics, Canberra. B.A.E. Australia (1961). Statistical Handbook of the Sheep and Wool Industry, Third Edition. Bureau of Agricultural Economics, Canberra. B.A.E. Australia ( 1962). The Australian Sheep Industry Survey, 1957-1960. Bureau of Agricultural Economics, Canberra. B.A.E. Australia (1963). The Beef Situation, No. 8. Bureau of Agricultural Economics, Canberra. F OLEY , J. C. (1957). Droughts in Australia. Bureau of Meteorology, Australia. Bull. No. 43. H YLAND , P. G. (1960). Lamb losses in Victoria. WooZ Technology and Sheep Breeding 7: 87. W ATSON , R. H. (1957). Wastage in reproduction in Merino sheep. Australian Veterinary Journal 33: 307. W ATSON , R. H. ( 1962). 'The Simple Fleece', p. 18 (Ed. A. Barnard) (Melbourne University Press). 128