Managing metabolic disorders in pregnant ewes to improve ewe and lamb survival

Suboptimal levels of lamb survival are the largest contributor to reproductive wastage in Australian sheep flocks (Kleemann & Walker 2005), with an average 20% of lambs born dying mainly within 3 days of birth (Hinch & Brien 2014). This results in substantial loss of production, producer and industry income, and is increasingly being perceived as poor animal welfare. Improving lamb survival is therefore a priority for the industry. Dystocia and the starvation-mismothering-exposure complex are generally the major causes of perinatal lamb mortality, and in combination account for approximately 80% of deaths. Management to reduce mortality therefore needs to address these causes to be effective. Clinical deficiencies of calcium (Ca) and magnesium (Mg) contribute to both ewe and lamb mortality, but their incidence is typically low. There is an increased risk of these disorders on lush, grass-based pastures, due to lower levels of calcium and magnesium in grasses than legumes. The role of sub-clinical deficiencies in lamb survival is less clear, but potential mechanisms include a reduction in muscle contractions and cervical dilation increasing the duration of parturition (leading to dystocia), appetite suppression, and through poorer temperature regulation and neuronal injury in newborns. The aim of this project was to determine the extent of any reduction in calcium or magnesium during late pregnancy in ewes grazing common pastures; whether this was associated with increased lamb mortality; and whether mineral supplementation could be used to improve the calcium and magnesium status of reproducing ewes, reducing the incidence and consequences of sub-clinical hypocalcaemia and hypomagnesaemia, in particular, lamb mortality.