Abstract:
A STUDY OF REPRODUCTIVE WASTAGE AMONG COMMERICAL SHEEP FLOCKS GRAZING OESTROGENIC PASTURES IN SOUTH WESTERN AUSTRALIA R.H. WROTH* and R.J. LIGHTFOOT* Summary Reproductive wastage was investigated over two seasons in ten Merino flocks grazing pastures based on oestrogenic subterranean clover. Only 65 percent of ewes were served during the first 16 days of joining. Ovulation rates were low, averaging 1.13. Fertilization rates (73%) were low when compared with flocks unaffected by oestrogenic pastures. Embryonic mortality varied considerably between properties and years averaging 27 percent. I. INTRODUCTION There is evidence to suggest that in the high rainfall zone of south Western Australia where ewes graze pastures based on oestrogenic subterranean clover, fertility is depressed by at least 8 percent (Lightfoot, 1972). The work reported here was conducted to define and quantitate the major components of ewe infertility in this zone and, by comparison with the concurrent studies of Marshall, Beetson and Lightfoot (1976), to gauge the effect that oestrogenic pastures have on these components. Such information is essential before remedial action can be planned. ' II. MATERIALS AND METHOD For the 1971 lambing, 400 ,Merino ewes were selected on each of 10 properties (approx. 250 km south-east of Perth, 500 mm rainfall) with pastures based on oestrogenic cultivars of subterranean clover (25 to SO%, Dwalganup, Dinninup or Yarloop). Two hundred of these had been mated at 1% years to lamb for the first time in 1970 (young ewes) and the rest were the oldest ewes on the property (old ewes). In 1972, 200 'young ewes*! were added to each flock, the 1971 'young ewes?* were incorporated into the **old ewe' group, while age culling greatly reduced . the number of original *lold ewes'*. The total numbers of ewes studied in 1972 ranged from 389 to 590, averaging 474. As far as possible all flock operations such as time of joining, ram selection, ram percentage (1.75 to Z.S%), shearing, etc. remained as per normal farm practice. Rams were, however, fitted with Sire Sine harnesses and service records were obtained on days 4, 5, 11, 12, 16, 28 and 42 (end of joining). Ewes recorded as served on days 5 and 12 (mean 49 t 4 ewes/property/year) were examined by laparotomy on days 7 and 14 respectively. The number of corpora lutea were recorded and the ova collected by flushing the fallopian tubes with saline. Cell cleavage was taken to indicate fertilization. Prior to lambing, ewes were segregated into three groups. Group 1 consisted of non-returns to service during the first 16 days of joining and diagnosed as pregnant by ultrasonic examination and udder inspection. Group 2 were served post day 16 but diagnosed pregnant as above, while Group 3 included all ewes diagnosed as non pregnant. On days 21 and 42 of lambing ewes in each group were examined and classified as either lambed, lambed and lost, pregnant or dry. * Department of Agriculture, South Perth, Western Australia, 6151. 225 . The above service, surgical and lambing observations were adopted to give a detailed partition of ewe fertility during the first cycle (days l-16) of joining. Where appropriate, the means for all properties ? Standard Error are presented. Statistical significance was examined by t test or Chi-square. III. RESULTS Basic data for each flock are summarized in Table 1. The incidence of service (,days l-16) among young ewes was lower (64 v 69%, P < 0.05) and more variable than that for the older groups. Overall, the proportion of ewes served in this period (65%) was significantly lower (P < 0.001) than that expected (94%) if one assumes a 17 day oestrous cycle and all ewes had commenced regular cyclic oestrous activity before the rams were joined. The proportion of ewes served increased as the time of joining advanced from November to March. The linear regression (P < 0.001) for all properties and years was: % ewes served (days l-16) = 34.5 + '0.44 (k 0.09) X , where X = number of days from November 17 to the date of joining. By days 28 and 42, 92 t 2 and 96 2 1 percent respectively of ewes had been served. Of the '*unservedrr ewes, 21 2 5 percent actually lambed, indicating a degree of error in service observations. With only isolated exceptions ovulation rates were low and exhibited comparatively little variability. In both years ovulation rates were lower for young than for old ewes (1.06 v 1.18; P < 0.05). The proportion of ewes yielding fertilized ova varied between years according to age group (Table 1). On overall pooled data, the fertilization rate from service on day 5 (67%) was significantly lower (P < 0.01) than that from service on day 12 (78%). Old ewes had reduced numbers of spermatozoa on fertilized ova (35 v 21% ova with less than six sperm, P < 0.01) when compared with young ewes, the effect being most marked in 1971 when the average age of the 'old ewes** was greater. . The percentage of ewes lambing to first service during days 1 to 16 of joining increased (P < 0.01) as the joining advanced. Means for I service on days 1 to 4, 5 to 11 and 12 to 16 were 47 + 3, 56 2 4 and 58 k 3 percent respectively. Lambing to service from days 17 to 42 were 61 ? 3 and 5.1 2 3 percent for ewes not previously served and returns to first cycle service respectively. Ewes examined by surgery and excluded from the lambing data in Table 1 because eggs were removed following first , cycle service, averaged 60 & 2 percent ewes lambing. IV. DISCUSSION The observations on service incidence during days 1 to 16 of joining suggest that many ewes were not exhibiting cyclic oestrus activity when the rams were joined. This effect was more marked in young ewes and among flocks joined prior to mid February. Most ewes were served by day 28, suggesting a 'teaser effect? Ovulation rates were low for almost all properties in both years with no apparent improvement as the breeding season advanced - confirming the recent findings of Lindsay et al. (1975). -The effects of prolonged grazing on pastures containing oestrogenic subterranean clover were seen most clearly in increased returns to service (35 v 19%), reduced fertilization (73 v 93%), and reduced numbers of spe<atozoa on fertilized ova (29 - 99- ova with less than 6 sperm, vo 226 TABLE 1 SUMMARY OF RESULTS P < 0.001) when compared with the concurrent study by Marshall, Beetson and Lightfoot (1976) of ewes grazing non-oestrogenic pastures. The estimates of embryonic mortality varied greatly between properties and years. Much of this variability was due to a lack of statistical precision caused by low ewe numbers and compounding of errors in estimates of fertilization and lambing rates. Two points, however, warrant highlighting. First, the overall estimate of 27 percent is based on **all or none** loss of pregnancy on a ewe basis. It therefore underestimates total embryonic mortality, as additional wastage occurs due to partial loss in multiple ovulating ewes. This would be minimal in the present study, however, due to low ovulation rates. Secondly, the estimate of embryonic mortality, -when based on non-returns to service was approximately one half of that based on lambing rate (13 ? 3 v 27 t 3%). It seems reasonable to conclude, therefore, that approximately 50 percent of embryonic losses occurred relatively late in pregnancy - sufficient at least to delay return to service for 26 to 42 days. The observations on lambing in relation to date of service indicate that conception rates tended to increase during the first 16 days of joining. This effect is similar to that reported recently by Knight, Oldham and Lindsay (1975) who observed reduced conception to service over days 1 to 14, compared with 15 to 28. The present study, together with that of Marshall, Beetson and Lightfoot (1976), suggests that the infertility is most apparent during the first few days of joining and is associated with reduced fertilization. Estimates of the theoretical improvement in percent ewes lambing likely to result from reductions in losses due to individual wastage parameters during a 42 day joining were calculated as outlined by Marshall, Beetson and Lightfoot (1976). The calculations predict that if service incidence on days 1 to 16 was increased from 65 to 94 percent an extra 4 percent ewes would lamb. Extending the joining period by an additional 14 days to 8 weeks overall should increase the proportion of ewes lambing by approximately 5 percent. Similarly, if fertilization rate increased from 73 to 93 percent (as found by Marshall, Beetson and Lightfoot, 1976, for a non-oestrogenic situation) the calculations suggest that an additional 10 percent more ewes would lamb. v. ACKNOWLEDGEMENTS . The authors express sincere gratitude to the farmers (Messrs Marsh, Ness, Harrison, Doudle, Rajander, Edkins, Lubcke', Byrne, Pascoe and South), who co-operated in this study. Skilled assistance was provided by MS Helen Nicol and Messrs 0. Ashby and B. Guthrie. The project was supported by grants from the Wool Research Trust Fund. VI. REFERENCES KNIGHT, T.W., OLDHAM, C.M. and LINDSAY, D.R. (1975). Australian Journal of agricultural Research &: 577. LIGHTFOOT, R.J. (1972). Journal of Agriculture Western Australia 13: 102. LINDSAY, D.R., KNIGHT, T.W., SMITH, J.F. and OLDHAM, C.M. (1975). Australian Journal of agricultural Research 26: 189. -= MARSHALL, T., BEETSON, B.R. and LIGHTFOOT, R.J. (1976). Proceedings of the Australian Society of Animal Production 11: (In press). 228