Abstract:
THE FERTILITY OF EWES GRAZING PASTURES CONTAINING DIFFERENT PROPORTIONS OF SUBTERRANEAN CLOVER IN SOUTH WESTERN AUSTRALIA H. LLOYD DAVIES* and R. A. MALLER Summary Medium Peppin Merino ewes grazed pastures of approximately 100 per cent, 60 per cent, 30 per cent and 0 per cent subterranean clover (cv. Yarloop) for a period of three years and their reproductive performance was recorded over four years. The percentages of ewes pregnant in the final year of the experiment in relation to treatment were as follows:-100 per cent clover - 53 per cent; 60 per cent clover - 63 per cent; 30 per cent clover - 77 per cent; no clover - 88 per cent. The results indicate that the botanical composition of a pasture offered to grazing ewes may be associated with changes in fertility. I. INTRODUCTION It is well recognized that some of the reduction in lambs marked from sheep grazing subterranean clover pasture in the agricultural regions of Western Australia can be ascribed to the intake of phyto-oestrogens (Bennetts, Underwood and Shier 1946; Beck and Gardiner 1965). Several methods have been suggested for the control of oestrogenic infertility. These include the use of pastures of low clover content (Beck and Gardiner 1965). In the absence of experimental assessment of the effect of botanical composition on sheep fertility, an experiment was undertaken to measure it. II. MATERIALS AND METHODS (a) Experimental The purpose of the experiment was to permit ewes to graze pastures of the following approximate botanical composition:- * C.S.I.R.O. Division of Plant Industry, Western Australian Laboratories, Wembley, Western Australia. Present address: M. C. Franklin Laboratory, University of Sydney Farms, Camden, New South Wales. t C.S.I.R.O. Division of Mathematical Statistics, Western Australian Laboratories, Wembley, Western Australia. 100 per cent clover; 60 per cent clover; 30 per cent clover; t No clover, grass only. The work was carried out at the C.S.I.R.O. Research Station, 'Glen Lossie', Kojonup, Western Australia. Details of the environment at Kojonup have been given by Davies (1962). A 40.5 ha area of virgin country was cleared in 1964 and subdivided into four plots each of 10.1 ha. Plot 1 ( 100 per cent clover) was sown with Yarlmp subterranean clover. Plots 2 and 3 (60 per cent and 30 per cent clover respectively) were sown with a mixture of Yarloop and Wimmera rye grass. Plot 4 (no clover) was sown with Wimmera rye grass alone. All plots were top dressed annually with approximately 200 kg/ha of superphosphate. In addition, Plot 2 was top dressed with 27.0 kg of N as urea (46% N) applied as split dressings of 13.5 kg in the autumn and 13.5 kg in the spring. Plot 3 received 27.0 kg N in the autumn and 27.0 kg N in the spring. Plot 4 was treated similarly. In addition, Plot 4 was sprayed with an appropriate proprietary herbicide if any areas of subterranean clover were observed. In late September of each year except 1968, estimates of botanical composition were made. On each occasion, 40 quadrats 25 cm x 25 cm were taken on each plot on a basis of restricted randomization, and botanical composition was estimated visually on each sample. A check on the visual assessment was made by cutting some samples and sorting. Fifty maiden, medium Peppin Merino ewes were allocated at random to each plot. They were weighed a week before mating started, at the end of mating, six weeks before lambing was due to commence and at the beginning and end of lambing. They were joined to Merino rams, one ram per plot, and the rams moved from plot to plot on each Monday. Mating took place over six weeks from midFebruary to the end of March. The plots and ewes grazing thereon were examined twice daily during the peak of lambing and at least once daily at other times. The lambs were weighed daily between 9 and 11 a.m., eartagged and the dam identified. From February 1968, the ewes grazed as one group on a grass-dominant pasture and were mated as one group from February to March 1968. In July 1968, they were removed to the W.A. Department of Agriculture Field Station at Merredin to record their final lambing performance. Percentages of ewes lambing, ewes twinning and lambs surviving to marking were compared between treatments and years by partitioning the heterogeneity of x2 into relevant components (Lancaster 195 1). III. RESULTS Table 1 gives the botanical composition for 1965-66-67. This table shows that the desired botanical composition was attained. Although there were deviations from the planned composition, these were of small account. 395 (i) (ii) (iii) (iv) - (b) Statistical Methods (a) Pasture Data TABLE 1 (b) Liveweight of the Ewes The Iiveweight of the ewes was used as a criterion for supplementary feeding. This became necessary on the 100 per cent grass and 30 per cent clover plots in the autumn of 1966 when bodyweight on these plots fell to 35.0 kg. 0C Ewes Lambing The proportion of ewes lambing is shown in Table 2. The table shows that, in the first year ( 1965), the ewes on the 'no clover' and 30 per cent clover plots had a lower lambing percentage. In 1966, there were no differences between treatment in percentage ewes lambing. In 1967, there were significant differences (P<O.O5) between the 100 per cent and 60 per cent clover treatments and the 'no clover' and 30 per cent clover treatments. The difference increased in 1968 when only 53 per cent of the ewes on the 100 per cent clover lambed compared with 88 per cent on the grass-only plot. Only 2 per cent of the experimented ewes lambing had twin lambs in 1966, 8 per cent in 1967 and 26 per cent in 1968. There were no differences in percentage of ewes twinning due to treatment, but there were clear differences due to year. 396 TABLE 2 (d) Lambing Losses Lamb losses did not differ significantly between treatments. The percentage of lambs marked tended to reflect the pattern for percentage ewes lambing (Table 3 ) . In 1968, the 30 per cent clover was an exception to this pattern because only 5 ewes had twins on the 30 per cent clover plot compared with 12 on the 'no clover', 8 on the 60 per cent clover and 9 on the 100 per cent clover. IV. DISCUSSION Low fertility of ewes is a most important pathological effect and an important economic loss in sheep grazing oestrogenic subterranean clover in Western Australia (Gardiner and Naim 1969). The cultivar Yarloop is known to have high oestrogenie activity (Davies and Dudzinski 1965). By 1968, both the proportions of pregnant ewes and the percentage lambs marked were considerably lower in the group previously grazing the 30 per cent clover plot compared with that previously grazing the 'no clover' plot. Depression in percentage ewes conceiving and percentage lambs marked has been observed previously (Davies 1965) when the clover component in the pasture was less than 30 per cent. At mating time, the ewes on the 60 oer cent clover and 100 per cent clover plots were heavier than those on the 'no clover' and 30 per cent clover plots. For this reason, it is unlikely that any of the infertility on the high clover plots was due to low liveweight at mating. Although the desired botanical composition was attained in these plots, it is not known whether the botanical composition o,n offer bears any relation to the relative amounts of grass and clover consumed by the sheep. However, the establishment of an experiment with an adequate number of ewes to investigate fertility differences in sheep being fed the correct ratio of green clover and grass for a number of years would be prohibitively expensive and tedious. 397 TABLE 3 The role of the grass component in pasture, when associated with an oestrogenie legume, is unknown. Probably, the grass acts as a simple diluent to the total intake of phyto-oestrogens. However, the addition of grass may also affect the rate and extent of breakdown of isoflavones in the rumen. Nilsson, Hill and Davies ( 1967) shlowed that the concentration of equol (an oestrogenic metabolite of formononetin) is dependent upon a quality factor in the ration. The results of this experiment suggest that one method of reducing the ewe infertility is to ensure that ewes do not have access to pastures with more than 30 per cent oestrogenic clover - particularly where cultivars as potent as Yarloop are sown. Undoubtedly, economic considerations have to be borne in mind in achieving a low` clover content - for instance, one would certainly hesitate to advocate the use of nitrogen fertilizer merely to control subterranean clover disease. Neverth.eless, the use of nitrogenous fertilizers and, if necessary, selective herbicides and grazing management practices, including using lower stocking rates which would ensure a low level of clover in the pasture, could be other weapons for overcoming the depredation of this disorder. V. ACKNOWLEDGMENTS The authors are particularly grateful to Mr. H. G. Neil, Officer-in-Charge, Sheep and Wool Branch, W.A. Department of Agriculture, who assumed responsibility for the ewes from the experiment in July 1968 and recorded their lambing performance. Mr. J. Charlick and Mr. H. Simpson gave invaluable technical assistance during the course of the experiment. VI. REFERENCES B ECK, A. B., and G ARDINER, M. R. ( 1965). J. Dep. Agric. West. Aust. 6: 390. B ENNETTS, W. H., U NDERWOOD , E. J., and S HIER , L. F. (1946). Aust. vet. J. 22: 2. D AVIES, H. L LOYD (1962). Proc. Aust. Soc. Anim. Prod. 4: 113. D AVIES, H. L LOYD (1965). Ph.D. Thesis. Univ. of W.A. D AVIES , H. L LOYD , and D UDZINSKI , M. L. (1965). Aust J. agric. Res. 16: 937. G ARDINER , M. R., and N AIRN, M. E. (1969). Aust. vet. J. 45: 215. L ANCASTER , H. 0. (1951). JZ. R. statist. Soc. (Series B). 13: 242. NILSSON, A., H ILL, J. L., and D AVIES, H. L LOYD (1967). Biochim. biophys. Acta 148: 92. 399