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Individual variation in milk composition over lactation in harbour seals (Phoca vitulina) and the potential consequences of intermittent attendance

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We studied milk composition over the course of lactation in 21 harbour seal (Phoca vitulina L., 1758) females on Sable Island, Nova Scotia. Milk fat content increased significantly from 40.8% ± 1.01% at parturition to 50.2% ± 1.39% at day 7 and then remained relatively constant throughout the remainder of lactation. Changes in dry matter mirrored changes in fat content. Protein content averaged about 9% over mid to late lactation. There was considerable between-individual variation in the composition of milk and how it changed over lactation, particularly in milk fat content (CV 9.1%–11.4%). In three females that were separated from their pups for 4–6 days, milk fat content declined by 20%–23% and milk protein content increased by 6%–11%. These changes in milk composition indicate that changes in mammary gland function occur rapidly following the onset of milk stasis in harbour seals. The rapid response of the mammary glands to separation suggests that, in direct contrast to the glands of otariids, the glands of harbour seals rely on regular evacuation to maintain normal function. These results suggest that there may be a significant physiological constraint on the duration that harbour seal females, and presumably other phocid seals, can forage without negatively affecting energy transfer to their pups.

Nous avons étudié la composition du lait durant la période d'allaitement chez 21 phoques communs (Phoca vitulina L., 1758) femelles sur l'île de Sable, Nouvelle-Écosse. Le contenu lipidique du lait augmente significativement de 40,8 % ± 1,01 % à la mise bas à 50,2 % ± 1,39 % au jour 7; il reste ensuite relativement constant pendant le reste de la période d'allaitement. Les variations de la matière sèche reflètent celles du contenu lipidique. Du milieu à la fin de la période d'allaitement, le contenu protéinique est en moyenne d'environ 9 %. Il y a des variations individuelles importantes de la composition du lait et des changements de composition au cours de l'allaitement, particulièrement du contenu lipidique (C.V. 9,1 % – 11,4 %). Chez trois femelles séparées de leurs petits pendant 4–6 jours, le contenu lipidique du lait a diminué de 20 % – 23 % et le contenu protéinique a augmenté de 6 % – 11 %. Ces changements de composition du lait indiquent que les modifications de la fonction de la glande mammaire se produisent rapidement après la stase du lait chez les phoques communs. La réaction rapide des glandes mammaires à la séparation laisse croire que, à l'inverse de celles des otariidés, les glandes des phoques communs dépendent d'une évacuation régulière pour maintenir leur fonction normale. Ces résultats indiquent qu'il peut exister une contrainte physiologique significative sur la période de temps que les femelles du phoque commun, et probablement aussi d'autres phoques phocidés, peuvent partir à la recherche de nourriture sans affecter négativement le transfert d'énergie aux petits.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2005-12-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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