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First published online August 17, 2007
Journal of Experimental Biology 210, 3043-3053 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.009381

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Effects of mass and body composition on fasting fuel utilisation in grey seal pups (Halichoerus grypus Fabricius): an experimental study using supplementary feeding

Kimberley A. Bennett^1,*, John R. Speakman², Simon E. W. Moss¹, Paddy Pomeroy¹ and Mike A. Fedak¹

¹ NERC Sea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, Fife, KY16 8LB, UK
² School of Biological Sciences, University of Aberdeen, AB24 2TZ, UK

^* Author for correspondence (e-mail: k.a.bennett{at}dundee.ac.uk)

Accepted 24 June 2007

This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in grey seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86–99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of grey seal pups.

Key words: protein depletion, fat reserves, energy use, fuel allocation, energy partitioning, first year survival