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Beyond the Bale : December 2018
AWI-funded research has shown that increasing the calcium and magnesium intakes of pregnant ewes that don’t show any visual sign of calcium or magnesium deficiency puts the ewes into a better metabolic state, improves the immune response in twin newborn lambs and increased their weights at four weeks of age. Although mineral supplementation alone may not result in significant increases in lamb survival in individual flocks when ewes are grazing common pastures, it is recommended as a low-cost risk management strategy for pregnant ewes (especially twin bearers) to improve lamb survival. As reported in the June edition of Beyond the Bale, an AWI-funded project at the Graham Centre for Agricultural Innovation at Charles Sturt University has been looking at whether more widespread supplementing of lambing ewes’ diets with calcium and magnesium can improve lamb survival. When a ewe goes down with metabolic disorders such as hypocalcaemia (milk fever) or hypomagnesemia (grass tetany) the effects are very obvious. But what this project was more interested in is subclinical metabolic disorders, which is when there are no visual signs that the ewe is in trouble but her magnesium and calcium levels are actually below requirement. To recap the June article: 1. A literature review was initially carried out, which indicated subclinical calcium and magnesium deficiencies might reduce lamb survival. 2. Monitoring of 16 commercial lambing flocks grazing typical pastures across NSW, SA, Vic and WA was then undertaken in 2016, which demonstrated that two-thirds of flocks had 20% of ewes deficient in either calcium or magnesium a week before lambing, indicating a risk of subclinical metabolic disease. 3. An intensive pen study with twin-bearing ewes was then carried out, which showed that mineral supplementation with calcium and magnesium improved energy balance regulation in the ewe, which should reduce the risk of the ewe developing complications such as twin-lamb disease. Furthermore, mineral supplementation improved the immune response in both ewes and lambs, proving a mechanism through which lamb survival might be altered. Lamb weight at four weeks of age was also improved by supplementation. However, the pen study did not contain sufficient ewes to determine if supplementation significantly improved lamb survival. Therefore further field trials were carried out to assess the impact on lamb survival of supplementation in grazing ewes on commercial properties. THE NEW FIELD TRIALS AND THEIR RESULTS In 2017, a study used five flocks (across NSW, SA, and WA) with control and supplemented groups. The supplement offered provided calcium, magnesium and sodium, but in a form (‘anionic salts’) designed to improve calcium metabolism. However, the mineral supplement was only consumed in amounts that could be effective by two of these flocks, and mineral supplementation did not improve lamb survival in either flock. The study was repeated in 2018 on another flock, comparing both standard (1:1:1 lime, Causmag and salt) and the previous ‘anionic’ supplement, to test whether the form of the supplement was an issue. In this study, both supplements were readily consumed near the target level, but their consumption did not improve lamb survival. The researchers suggest this lack of improvement in lamb survival might have been due to variability in ewes’ intake of the supplement during the field trials, or that other factors were of greater importance in affecting lamb survival in these commercial flocks. RESEARCH CONCLUSIONS A key research finding from the project was that many late pregnant ewes in Australian grazing flocks are subclinically deficient in calcium and magnesium, so woolgrowers should manage these risks to prevent clinical forms developing which could cause numerous ewe losses and high lamb mortality. When twin-bearing ewes consumed higher levels of calcium and magnesium (in the pen study), there was an improvement in the energy regulation of late pregnant ewes, the immune status of the lambs, as well as twin-lamb early growth rate – which can all be expected to reduce the risk of clinical metabolic disorders and other contributors to lamb mortality. Given the low cost of calcium and magnesium supplementation used in this project (<$0.02/ hd/day), the researchers say that provision of such supplements can be recommended as a low-cost risk management strategy for pregnant ewes, especially for twin bearing ewes or when ewes are being grain fed or grazing grass dominant pastures or cereal crops – because supplementation is likely to assist in prevention of some metabolic disorders and improve lamb immunity and early weight gains. ON FARM 49 MINERAL SUPPLEMENTS FOR PREGNANT EWES? Researchers say that calcium and magnesium supplements can be recommended as a low-cost risk management strategy for pregnant ewes, especially for twin bearing ewes or when ewes are being grain fed or grazing grass dominant pastures or cereal crops.
In the Shops - March 2019