The energetics of lactation in the Northern elephant seal, Mirounga angustirostris

• Published in: Journal of Zoology
• Main Authors: Costa, D. P., Boeuf, B. J. Le, Huntley, A. C., Ortiz, C. L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1986
• Subjects: Elephant Seal; Elephant Seals
• Online Access: http://dx.doi.org/10.1111/j.1469-7998.1986.tb03563.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1469-7998.1986.tb03563.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1986.tb03563.x; https://zslpublications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1986.tb03563.x

The energy and material transferred from Northern elephant seal mothers to their pups during the 26.5‐day lactation interval was measured using mass change and water influx data. The dilution of tritium‐ and deuterium‐labelled water was monitored in six female elephant seals and their pups. During the nursing period, pup mass increased by 10.4% of the initial body mass per day while females lost 4.19% of their initial body mass per day. Over the entire nursing period, females lost 42.2±4.9% of their initial body mass. Maternal mass transfer to the pup was efficient; pups gained 54.9% of the mass lost by their mothers. Females lost only 14.9% of their lean mass compared to 57.9% of their adipose mass. The fasting metabolic rate of females was 66.2±7.5 MJ/day, 2.41 times the predicted standard metabolic rate (SMR) of a terrestrial mammal of equal size; the total energy output was 163±11 MJ/day, 5.98 times the predicted SMR. Energy consumption for the entire lactation interval was 4330±460 MJ. Milk production accounted for 60% of this energetic expenditure. This efficient milk production was made possible by temporal separation of lactation and feeding. Separation of feeding from lactation confers several energetic and ecological advantages: reduction in the metabolic overhead used for maintenance metabolism onshore, reduction of foraging effort required to meet the demands of lactation, since feeding can be spread out over a significantly longer interval, and a greater flexibility while foraging at sea due to the absence of the pup.