Hypothermia is a real risk for newborn lambs and calves - and is a significant cause of loss of newborns born outdoors during cold weather.   When body heat is lost to the environment faster than a lamb or calf can replenish core body heat from within, hypothermia is likely. What factors influence the amount of heat that a lamb or calf can generate to keep itself warm, from the 'inside-out'?In our latest podcast, we investigate how mother nature has designed a range of inbuilt systems that help newborn lambs and calves stay warm. The importance of brown fat reserves is explained and other mechanisms such as muscle shivering are explored. Farm-level factors, specifically the nutrition of the pregnant ewe determine the extent of brown fat deposition in the unborn lamb. Keeping ewes in good body condition from mating to scanning, then from scanning to lambing favours better reserves of brown fat in unborn lambs and calves. More brown fat available at birth helps lambs and calves keep warm during the first few hours of life - potentially reducing risk of hypothermia in newborn ruminants.