The energetics of lactation: accurate measurements from a large wild mammal, the Grey seal (Halichoerus grypus)

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Abstract
Female Grey seals transfer large amounts of energy rapidly and efficiently to their pups. Using information from serial weighings and from carcase analysis the energy costs of repro duction and the efficiency of lactation for female Grey seals have been calculated. Females use over 125·6 MJ/day for maintenance and milk production. Pups consume 71·2 MJ/day in milk and can convert 58·6 MJ/day into growth and stored fat. The gross efficiency of the transfer from mother to pup is about 57%. Over 80% of the females' energy reserves are used to feed their pups. This massive transfer of resources in a short time period is thought to be an adaptation of an offshore aquatic feeder which has to return to land to give birth.