Abstract:
THE EFFECT OF SELENIUM TREATMENT ON THE FERTILITY OF MERINO SHEEP L.R. PIPER*,B.M.BINDON*,J.F.WILKINS**, R.J.COX**,Y.M. CURTIS* and M.A. CHEERS* SUMMARY Selenium treatment was given to both ewes and rams prior to mating and the effect on subsequent fertility was examined. Rams received either 0 or 5.0 and ewes 0, 2.5, 5.0 or 10.0 mg Se orally three weeks prior to joining. Ewes were blood sampled and slaughtered 30 days after their last recorded service and their reproductive tracts examined. There was a significant effect of ram treatment on conception rate. Ewetreatment did not influence ovulation rate, but had significant effects on the number of normal embryos recovered. Whole blood selenium status of individual sheep was closely related to dose but there was no clear relationship with reproductive performance. INTRODUCTION Selenium defi ion in a number 0 (.Hartley and Grant beneficial effects Australian studies response ('Gardiner et al. -m 1970; Wilk situations. ciency has been found to caus f domestic livestock species. 1961; Hartley 1963; Scales of selenium supplementation are inconsistent, with some et al. m- 1962; Davies 1966; ins 1980) observing positive #e various disorders of reproductIn sheep, New Zealand workers 1974) have reported many cases of on the fertility of ewes. However, workers reporting little or no Maxwell 1972) and others (Godwin fertility responses in some Hartley (1963) showed that the infertility he observed in Romney ewes in New Zealand was caused by embryonic mortality estimated to have occurred between 20 and 30 days after fertilization, and that such failure could be greatly reduced by selenium supplementation given prior to joining. In Wilkins' (1980) study, the nature of,the syndrome, as indicated by patterns of mating, was in agreement with that described by Hartley (1963). MATERIALS AND METHODS Environment The experiment was conducted in autumn 1977 at the CSIRO 'Longford' Field Station 37 km north-west of Armidale, N.S.W. The environment has been described by Hartridge (1979) and the sheep management by Turner (1978). The original native pastures, typical of granite-derived soils in the region had been progressively replaced by improved pasture species using procedures commonly adopted in the area (Anon. 1964). A total of 1.8 tonnes/ha of superphosphate (including 128 g of MO/ha). had been applied during the period 1964-1977. CSIRO Division of Animal Production, Armidale, N.S.W. 2350. ** Agricultural Research Centre, R.M.B. 944, Tarclworth, N.S.W. 2340. 241' Animal production in Australia Experimental procedure Two hundred and twenty-four mixed age Merino ewes were randomly allocated to eight groups for single sire joining with Merino rams aged 18 months. Both ewes and rams were medium Peppin strain and were born and reared on 'Longford'. In four of the sire groups the rams were given 5.0 mg Se and four were left untreated. The 28 ewes within each sire group were further randomized to provide treatments of 0, 2.5, 5.0 and lo,0 mg Se. All selenium treatments were administered orally-as sodium selenite three.weeks prior to the start of a 35-day joining period, after which the entire rams were replaced with vasectomised rams for a further 21 days. Rams were fitted with mating harness (Radford et al. 1960) and mservice records were obtained daily from the start of joining (19 April 1977). Ewes were considered 'pregnant' and were bled and slaughtered 30 days after their last recorded service by entire rams provided they were not raddled subsequently by the vasectomised rams, The remaining ewes, consisting of those not served (11) and those returning to service (28), were judged 'not pregnant' and were not slaughtered but were bled at the same time as the last slaughter group. Reproductive tracts were recovered at slaughter and contents removed, weighed and examined using procedures described by Bindon (1971). Selenium status of each ewe was assessed by the method of Peter (1980) from the whole blood activity of glutathione peroxidase (GSH-Px:E.C.1.11.1.9). The enzyme unit (E.U.) so determined was equivalent to 1~ mol NADPH oxidised/min at 37OC, using 0.7 mM t butyl hydroperoxide as substrate. In addition, direct estimates of the mean selenium levels were obtained by the method of Brown and Watkinson (1977) using bulked samples from each ewe treatment group. Statistical analyses The data were initial model for treatment and the the interaction of interaction or the included only the examined by chi-square and/or least squares <methods. The _ the least squares analyses included effects due to ewe and ram interaction between them, ram effects within ram treatments and this effect with ewe treatment. In no case did this latter individual ram effects reach significance and the final model ram and ewe treatment effects and their interaction. RESULTS Selenium status There were highly significant differences (PKO.01) between ewe treatment groups in GSH-Px activity in whole blood with the means being linearly related to dose (Table 2). The same pattern was evident in the selenium levels of the bulked samples from each group (Table 2). Ewes joined with treated rams had significantly higher enzyme activities than those joined with untreated rams (7.7 + 0.2 vs 6;8 2 0.3 E.U./g haemoglobin, P<O.Ol).. Selenium status of rams was not measured. Fertility The proportions of ewes 'pregnant' as defined above were not affected by ewe treatment but there was a significant difference (WO.05) in favour of those ewes joined with selenium-treated rams (Table 1). There was no difference between ram treatments in the percentage of ewes not served (4 + 2 vs 6 + 2). The above difference was therefore the result of greater numbgrs of ew% from some 242 Animal production in Australia untreated ram groups returning to service after the 35 day joining. Though not significantly different, the same pattern was evident during the 35 day joining (27 - 5 vs 16 - 4). + + TABLE 1 The effect of selenium treatment on fertility - %'pregnane'(+ SE). 0 86 (7) 86 (-7) 86 (5) Ewe treatment (mg Se) 2.5 5.0 75 (7) 81 (-7) 79 (5) 68 (7) 93 (7) 80 (5) 10.0 79 (7) 93 (7) 86 (5) Mean 77 (4) 88 (4) 83 (3) Ram treatment 0 5 Mean Ovulation rate and embryo loss There were significant (,P<O.OS) differences between ewe treatments in numbers of normal embryos per ewe and per ovulation but not in ovulation rate, total conceptus weight or in crown/rump length of normal embryos. There were no significant effects of ram treatment on any of these parameters. With the exception of blood selenium levels and enzyme activities, the least squares means for the various parameters presented in Table 2 showed no clear relationship to dose. For the two measures of embryo number (per ewe and per ,ovulation) the control mean did not differ significantly from the mean of the treated groups, but the mean of the highest dose group was significantly above @<O.OS) the mean of the other treated groups. Pooled group comparisons showed that the wastage rate of single ova, combining the 10.0 mg and 5.0 mg ewe treatments, wasless when compared to treatments 0 and 2.5 mg (x21 = 5.3, PCO.05). The wastage rate of double ovulations was significantly reduced (xl = 4.7, P<O.OS) in only the 10 -0 mg treatment group compared to the rest. TABLE 2 The effect of ewe treatment on selenium status and reproductive function. Least squares means (+ SE) for slaughtered ewes* 0 Ewe treatment (mg Se) 5.0 2.5 10.0 Character 1,79(0.08) 3 1.59(0.09)~ 1.67CO.08) 1.61(0.09) Ovulations/ewe 1.27(0.11) 0.80(0.11) 1.12(0.11) Normal embryos/ewel.l.O(O.lO) Normalembryos/ 0.72(0.06) 0.49(0.06) 0.68(0.06) O-66(0.06) ovulation GSH-Px activity 7.6 (0.4) 12.1 (0.3) 5.8 (0.4) 3.4 (0.3) (E.U./gHb) Selenium level 22 47 17 35 (ngSe/ml whole blood) * Total number of ewes was 179 except for enzyme activity (165) and whole blood Discrepancies from the number of selenium where bulked samples were analysed. pregnant ewes (185) were due to missing data. DISCUSSION , The wastage of ova shed was considerable in proportions of normal embryos recovered compared Hartley (1963) found doses as low as 1 mg to be situations and the apparent lack of response to is therefore difficult to explain. all groups as evidenced by the to ovulations present (Table 2). effective in some infertility low Se doses in our experiment 243 Animal production in Australia While there was a highly significant correlation (P<O.Ol) between dose rate and a ewe's GSH-Px activity in whole blood at slaughter, there was no apparent relationship between enzyme activity and embryo survival for individual ewes within groups. Thus enzyme activity in whole blood taken at this stage of gestation did not reflect the responsiveness of individual animals in the experiment. The total wastage observed here occurred within 30 days after service. Embryonic loss apparently occurred some time after implantation as judged by the size of the degenerating embryos and the amount of associated placental material. Placental function and'embryonic growth and survival are directly dependent on ovarian progesterone secretion during this period (Alexander and Williams 1966; Bindon 1971) and effects such as those observed here can be reproduced by ovariectomy before day 50 of pregnancy. It may therefore be useful to study plasma progesterone levels in Se deficient ewes up to day 30 of pregnancy.. There is little information available concerning the influence of selenium on fe.rtility in the male (Hidiroglou 1979). The effect of ram treatment on ewe fertility has not been previously reported and requires further investigation. Sire groups were assigned at random to individual paddocks for the joining period but, by chance, those paddocks allocated to the treated ram groups may have had higher levels of selenium in the pasture. This could explain the apparent effect of ram treatment on the selenium status and fertility of the ewes but direct effects on the male cannot be excluded. We would not expect Se treatment to have affected spermatogenesis in the time period involved, but effects on the Se content ofseminal plasma or on the fertilising capacity of semen are possible. ACKNOWLEDGMENTS We would like to thank Mr. J, Bowles for selenium analyses. The financial support of the Australian Meat Research Committee is gratefully acknowledged. ALEXANDER, G. and WILLIAMS, D. (1966). J.Endocr. 34 : 241. ANON, (1964). ''Soil and pasture research on the Northern Tablelands, New South Wales'. CSIRO (Agricultural Research Liaison Section : Melbourne). BINDON, B. M. (1971)- Aust.J.Biol.Sci. 24 : 131. BROWN, M. W. and WATKINSON, J. H. (1977).Anal.Chim.Acta. 23 DAVIES, H. L. (1966). J.Aust.Inst.Agric.Sci. 32 : 216. GARDINER, M. R., ARMSTRONG, J., FELS, H. and GENCROSS, R. N. (1962). Aust.J. Exp.Agric.Anim.Husb. 2 : 261. 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