Blood metabolites as indicators of nutrient utilization in fasting, lactating phocid seals: does depletion of nutrient reserves terminate lactation?

• Published in: Canadian Journal of Zoology
• Main Authors: Mellish, J E, Iverson, S J
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2001
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Cystophora cristata
• Online Access: http://dx.doi.org/10.1139/z00-208; http://www.nrcresearchpress.com/doi/pdf/10.1139/z00-208

Metabolites of lipid (free fatty acids (FFA) and β-hydroxybutyrate (βHBA)) and protein (blood urea nitrogen (BUN)) oxidation were measured during lactation in 18 female grey seals (Halichoerus grypus) and 6 female hooded seals (Cystophora cristata) as indicators of nutrient depletion and possible cues for pup weaning. FFA levels were high during lactation in both grey seals (51.2 ± 2.3 mg·dL -1 ) and hooded seals (67.0 ± 8.1 mg·dL -1 ), and levels were primarily related to the rapid lipid mobilization required for their high respective milk-fat outputs (P = 0.002). βHBA concentrations were negligible throughout lactation in both species (0.30 ± 0.14 and 0.03 ± 0.01 mg·dL -1 , respectively). Grey seals exhibited a decrease in BUN levels over the course of lactation (i.e., days 0-15, 39.3 ± 1.8 - 23.5 ± 3.3 mg·dL -1 , P < 0.001), which suggests protein sparing despite the added energetic cost of milk production over the 16-d lactation period. In contrast, hooded seals showed higher levels and no change in BUN levels (i.e., days 0-3, 43.2 ± 2.1 - 45.8 ± 2.1 mg·dL -1 , P > 0.3), suggesting that there is less need to spare protein in a species which lactates for only 3.6 d. Females of both species weaned their pups before entering stage III fasting, therefore metabolite levels do not appear to be a physiological cue for weaning.