The impact of melatonin supplementation during the final trimester of pregnancy on twin lamb survival and weight gain

Sutherland, Nicholas
University of Sydney


Neonatal lamb mortalities are a significant burden to the livestock economy and represent major welfare concerns for the industry, costing an estimated $540 million annual loss in production. On average, the industry suffers from pre-weaning lamb mortalities of up to 30% in twin-bearing ewes. The majority of these deaths (74%) occur within the first three days of birth, with the second-born lamb being most at risk. These deaths are predominantly attributed to starvation/mismothering, dystocia/hypoxia, exposure to adverse weather/environmental conditions, and predation. Previous studies have demonstrated that maternal melatonin supplementation during the final trimester of pregnancy reduces adverse effects of perinatal hypoxia and foetal growth restriction on the neonatal brain via increased placental efficiency, umbilical blood flow, and antioxidant actions. Lamb birth weight is a key driver to improved lamb survivability. Management factors that influence lamb survival include ewe condition, pasture cover, mob size, and stocking rate. The current study investigates the impact of melatonin supplementation during the final trimester of pregnancy on twin lamb survival and weight gain under commercial production conditions. The study was conducted across two commercial farms, one in Central West NSW (F1) and the other in the Riverina region of NSW (F2). Pregnant First-Cross and Merino mixed ages ewes were injected with 1 slow-release melatonin implant (18 mg, Regulin®) at gestational day 90. Control ewes received no injection. Ewes were monitored throughout the lambing period recording any ewe or lamb deaths. Lamb survival and weight were recorded at lamb marking and weaning time. Lamb survival and weaning rates in adult ewes grazing native pastures were increased in treatment groups (F1 MEL = 84%; F2 MEL = 89%) compared to control groups (F1 CTL = 81%; F2 CTL = 88%). Additionally, treatment groups recorded increased wet %, decreased lamb and loss, and ewe deaths. The was no lamb survival effect observed from ewes grazing on native pastures and maiden ewes. This suggests that melatonin performance is enhanced under nutritional and environmental stress. There was no weight gain effect observed between treatments between lamb marking and weaning. However, further studies are required to determine the long-term effect of melatonin supplementation on post-weaning performance and under different seasonal conditions.