| dc.description.abstract | Phocid seals are one of the few groups of mammals capable of sustaining the energetic demands of
lactation entirely through body nutrient stores while fasting. Lactation performance of the female
in turn influences the rate and pattern of pup growth. We examined variation in and patterns of milk
composition and production, maternal energy output, and pup growth and energy deposition over the
entire lactation period in 18 grey seal mother-pup pairs using hydrogen isotope ((H2O)-H-3 and D2O)
dilution. Milk composition was independent of maternal mass and nutrient stores, indicating
dependence on other physiological and genetic factors. Heavier females lactated longer (r(2) =
0.653, P < 0.001), had higher total milk outputs (r(2) = 0.652, P < 0.001), and produced
larger pups at weaning (r(2) = 0.417, P = 0.005). While fatter females lactated for longer periods
of time (r(2) = 0.595, P < 0.001), females with a larger lean body mass at parturition produced
more milk (r(2) = 0.579, P < 0.001). Total milk energy output was the strongest predictor of pup
weaning mass, which, along with the pup's efficiency of energy storage, accounted for 91% of the
variation in weaning mass. Nevertheless, there was sufficient plasticity in milk composition and
energy output that some smaller females produced relatively large pups. Few females appeared to
deplete body nutrients to the point where it might limit the duration of lactation. | en_US |
