Station, Omarama. Treatments first applied in April 1983 were: 1. Oral. Oral dosing of ewes with 5 mg Se as sodium selenate,. 3 weeks before joining with rams ...
(12) Cutress, T.W., Hunter, P.B.V., Davis, P.B., Beck, D.J. and Croxson, L.J. Adult Oral Health and Attitudes to Dentistry in New Zealand 1976. Dental Research Unit, MRC of New Zealand, Wellington, 1979. (13) Hunter, P.B.V. The prevalence of dental caries in 12- and 13-year-old New Zealand children in 1977 and 1982. N.Z. dent. J. 80:16-18, 1984. (14) Cutress, T.W., Hunter, P.B.V. and Hoskins, D.I.H. Adult Oral Heahh in New Zealand, 1976-1982. Dental Research Unit, MRC of New Zealand, Wellington, 1983. (15) Colquhoun, J. Dental fluorosis. The New Zealand Journal of Dentistry for Children, p.11-12, 1983. (16) Cutress, T.W., Suckling, G.W., Pearce, E.I.F. and Ball, M.E. Defects of tooth enamel in children in fluoridated and nonfluoridated water areas of Auckland. N.Z. dent. J. 81: 1984. (In press).
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Selenium supplementation alternatives: their effects on animal production, glutathione peroxidase and selenium levels in ewes and lambs
A.K. Metherell, J.L. Owens, C.G. Mackintosh and K. Turner* Invermay Agricultural Research Centre and *lnvermay Animal Health Laboratory Private Bag, Mosgiel, New Zealand INTRODUCTION Selenium supplementation of ewes and lambs is an important management practice, necessary to achieve satisfactory production, in many areas of New Zealand (Andrews et al. 1968). Until recently direct administration of soluble selenium compounds either orally or by injection was the only method of selenium supplementation allowed under the Animal Remedies Act 1967. In 1982 regulations permitting selenium topdressing were gazetted (New Zealand Gazette 1982.) Recommendations for selenium topdressing have been based on complete coverage of the grazed area on a farm to give protection to all stock for 12 months, although partial appUcation has been suggested (Watkinson 1983). On properties under extensive grazing and/or low stocking rates complete coverage is an expensive method of supplementation. Alternatives are: 1. The topdressing of limited areas of pasture for grazing at strategic times. 2. The use of slow release selenium formulations such as intra-ruminal bullets or injectable barium selenate paste (Cawley & McPhee 1984). This experiment compares oral dosing with sodium selenate, the strategic grazing of selenium topdressed pasture in autumn and the injection of barium selenate. Effects on ewe fertility, the growth and survival of lambs, levels of glutathione peroxidase (a selenium-containing enzyme) and selenium in blood were measured. EXPERIMENTAL Five groups of about 40 Merino ewes (4 to 5 years of age) and their lambs grazed extremely selenium deficient pastures ( 3 - 1 7 ^g Se/kg DM) on irrigated flats on a Mackenzie high country yellow-brown earth at Tara Hills High Country Research Station, Omarama. Treatments first applied in April 1983 were: 1. Oral Oral dosing of ewes with 5 mg Se as sodium selenate, 3 weeks before joining with rams and 4 weeks pre-
lambing; and of lambs with 2 mg Se at tailing (4 weeks of age) and weaning (10-12 weeks of age). Barium selenate Subcutaneous injection of ewes in the neck with 50 mg Se as barium selenate paste (Deposel* ; Robert Young & Co (N.Z.) Ltd, Petone), 3 weeks before joining. Topdressing 4 Grazing of recently selenium topdressed pasture (650 /jg Se/kg DM), during the flushing and mating period, beginning 3 weeks before joining and continuing for 4 weeks. Topdressing 8 Grazing of recently selenium topdressed pasture (650—550 fjg Se/kg DM), during the flushing and mating period, beginning 3 weeks before joining and continuing for 6 weeks. Control No selenium supplementation. Lambs in treatments 2, 3, 4 received no selenium supplementation. The selenium topdressed pasture for treatments 3 and 4 was topdressed 2 weeks before grazing with 1 kg selenium prills/ha (10 g Se/ha as sodium selenate; Selcote® ; Mintech (NZ) Ltd, Nelson) using 30 kg diammonium phosphate (DAP)/ha as a carrier. The pasture for treatments 1, 2 and 5 was topdressed with 30 kg DAP/ha only. Animals from all treatments were run together on low Se pasture except when treatments 3 and 4 were grazing selenium topdressed pasture. Groups were also separated during lambing. Ewes were joined in May, lambed in October and lambs were weaned in January. Animal performance and whole blood selenium and glutathione peroxidase status of ewes and lambs was measured over 12 months.
RESULTS Animal performance There were more barren ewes in the control group than in the selenium supplemented groups (Table 1). Mating records showed that almost all barren ewes in the control group had been mated in the first cycle but did not return to service in the second cycle. This is consistent with embryonic loss as the cause of barrenness. There were no differences between treatments in the number of lambs born per ewe lambing. The very low number of lambs tailed per ewe mated in the control group (Table 1) reflects both barrenness and perinatal lamb mortality (Table 2). Post-mortem examination of lambs from the control group in every case showed lesions typical of white muscle disease, a myopathy of cardiac or skeletal muscle. A lower lamb tailing percentage in the oral treatment group than in the barium selenate and topdressing treatments (Table 1) was due to higher lamb mortality in the first 28 days (Table 2). Cardiac lesions were observed in some lambs dying in the oral treatment group, but there was no indication of white muscle disease in lambs from the topdressing or barium selenate groups which died before 28 days. However, there were lesions of white muscle disease in lambs from the topdressing^ treatment which died at 10 weeks or older. Lamb birth weight did not differ between treatments, but the surviving lambs in the control treatment had much lower weight gains than lambs from the other treatments. There were small differences in liveweight between lambs in treatments 1,2,3 and 4. At 4 and 8 weeks of age lambs in the oral treatment were lighter, but subsequently liveweight gains were greater in the oral treatment. Post-weaning gains in the topdressing treatments were very low (Table 3). Blood selenium and glutathione peroxidase status At the start of the experiment the mean whole blood selenium and glutathione peroxidase (GSHPx) levels in the ewes were 17 /jg/l Se and 2.8 kU// GSHPx respectively. The GSHPx status of control ewes fell to extremely low levels, less than 1 kU// GSHPx, through the course of the experiment. The oral 88
treatment resulted in 3 to 5 kU// GSHPx, considered by the authors to be a marginally adequate level. The grazing of selenium topdressed pasture resulted in a rapid increase in GSHPx which continued for about 8 weeks after animals had been removed from the treated paddock. Group mean levels peaked 12 weeks after grazing started at 34 and 41 kU// GSHPx with 4 and 8 weeks grazing, respectively. After a plateau phase they fell rapidly during spring but remained adequate for most of the lactation period. Injection of barium selenate gave a very large and prolonged increase in GSHPx levels. The peak level of 51 kU// was reached after 21 weeks and after 12 months the mean level was still 17 kU//. In both the oral dosing and strategic topdressing treatments very low GSHPx levels, less than 1 yU//, were measured 12 months after the initial treatment. GSHPx levels in new born lambs closely reflected those in their dams, being on average 60% of their dams' pre-lambing level. GSHPx and Se in lambs fell rapidly during their first 4 weeks. Very low levels, less than 1 kU// GSHPx and 5 ^J%/I Se, were found in lambs from the control treatment and in lambs from both topdressing treatments after 20 weeks. High levels, greater than 5 kU// GSHPx and 20 /yg// Se, were maintained until 12 weeks in lambs born to ewes treated with barium selenate. GSHPx and Se levels increased after lambs had been given oral selenium. Blood selenium and GSHPx levels were strongly correlated. DISCUSSION Barium selenate injection or the grazing of pasture recently topdressed with selenium for at least one month during flushing and mating will increase the selenium status of ewes sufficiently to prevent selenium-responsive embryonic mortality, and the carry-over efect will prevent congenital white muscle disease in lambs. If the lambs from these treatments are not given supplementary selenium they are likely to suffer post-weaning ill-thrift and possibly delayed white muscle disease. With strategic grazing of selenium topdressed pastures by ewes in the autumn, lambs should be given selenium as early as possible, e.g. at tailing, and certainly at weaning. These strategies are at least as effective as conventional oral dosing or ewes and lambs. Under the conditions of severe selenium deficiency in this experiment there was some evidence that oral dosing of ewes at currently recommended rates and frequencies may not be adequate to avoid lamb mortality and reduced growth rates caused by selenium-responsive diseases.
Table 2: The effect of selenium treatments on lamb mortality (% of lambs born) Cumulative mortality % Treatment 4 weeks age 10-12 weeks age 18-20 weeks age (tailing) (Weaning) (March 19 19 19 1. Oral 22. Barium selenate 2 4 4 3. Topdressing 4 8 16 34 4. Topdressing 8 8 11 13 5. Control 79 100 100 Table 3: The effect of selenium treatments on mean lamb liveweight at weaning (10-12 weeks age) and in March (18-20 w eeks age). Adjusted for effects of birth rank and sex Liveweight (kg) Treatment Weaning March 1. Oral 17 22 22. Barium selenate 18 21 3. Topdressing 4 17 19 4. Topdressing 8 18 20 5. Control 9
The relationship between blood selenium levels and calf growth responses to selenium supplementation
A.J. Fraser* and D.F. Wright# * Ruakura Animal Heahh Laboratory, Hamilton, New Zealand # Agricultural Research Division, Ministry of Agriculture & Fisheries, Palmerston North, New Zealand BACKGROUND Selenium (Se) deficiency in sheep and cattle is widespread in New Zealand. The most widespread and economically important Se deficiency disease is considered to be Seresponsive illthrift, where Se deficiency results in condition loss and reduced growth in both sheep and cattle. Accurate diagnosis of Se deficiency is important to both ensure economic loss because of deficiency does not occur, and time and money is not wasted treating unresponsive animals. Carrying out a controlled weight gain response trial to Se supplementation is the definitive method of diagnosing Seresponsive illthrift. However, trials are costly in time and resources, and there is a delay in determining the outcome during which economic losses in untreated animals may occur. Blood Se analyses are now commonly used to diagnose Se deficiency of livestock. They have the advantages over trials of lower cost, greater convenience, quicker results, and can quantify the Se status of unresponsive animals. However, the usefulness of blood Se analysis depends on there being a good relationship between blood Se concentrations and growth response to Se supplementation, and a knowledge of other factors influencing Se responsiveness. Since Se was discovered to be an essential trace element in 1957, many Se growth response trials have been carried out in New Zealand. Some of these trials have been published, but many remain unpublished. Few New Zealand trials have been pubhshed for growth responses in cattle (1,4,5,6,7,10) and only one of these included measurement of blood Se levels(5), though blood Se levels measured at a later date have subsequently been reported for one other trial (10 in reference 3). There was thus clearly a need to bring together information from both published and unpublished cattle Se growth response trials in New Zealand, and use this information to define the relationship between blood Se levels and selenium growth response.
ACKNOWLEDGEMENTS The authors would hke to thank P.J. Cole and J. Rogers for animal management and recording, B.N. Hananeia for glutathione peroxidase analysis, K.E. Woodrow for selenium analyses, and J.M. Gill for pathological examinations. REFERENCES Andrews, E.D., Hartley, W.J. and Grant, A.B. (1968): Seleniumresponsive diseases of animals in New Zealand. N.Z. Veterinary Journal 16: 3-17. Cawley, G.D. and McPhee, I. (1984): Trials with a long acting parenteral selenium preparation in ruminants: Sheep. The Veterinary Record 114: 565-566. New Zealand Gazette 1982: 1235. Watkinson, J.H. (1983): Prevention of selenium deficiency in grazing animals by annual topdressing of pasture with sodium selenate. N.Z. Veterinary Journal 31: 78-85. Table 1: The effect of selenium treatments on lambing performance Ewes barren born per Lambs Treatment (% ewes perLambs ewe lambing ewe tailed mated joined) 1. Oral 8 1.30 0.98 2. Barium selenate 5 1.32 1.23 3. Topdressing 4 0 1.25 1.15 4. Topdressing 8 7 1.39 1.20 5. Control 28 1.26 0.19
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