Comparison of Ghrelin, Insulin-Like Growth Factor, and Growth Hormone Concentrations in Human and Common Pinniped Rehabilitation Formulas
Abstract
The growth rate in rehabilitated pinniped pups fed milk-based formula is significantly lower than that of free-ranging pups consuming maternal milk.1 In contrast, formula-fed human infants have a greater growth rate compared with breastfed infants.2 Human formula is known to contain greater quantities of ghrelin and insulin-like growth factor (IGF)-I than breast milk, and results in increased intake and growth rate.3 Ghrelin is a protein hormone that stimulates appetite.4 The release of IGF-I is stimulated by growth hormone (GH) and is responsible for mediating the anabolic effects of GH in most species.4,5 The presence of these hormones in milk suggests that they may be important for normal growth and development of infants. The slow growth rate of formula-fed pinnipeds may suggest that pinniped formulas have reduced concentrations of these hormones (ghrelin, IGF-I, and GH) compared with human formulas. Concentrations of ghrelin, IGF-I, and GH were quantified via radioimmunoassays6 in commercially available human formulas (n = 3) and pinniped rehabilitation formulas (n = 8) supplied by The Marine Mammal Center (Sausalito, CA), Mystic Aquarium (Mystic, CT), and Vancouver Aquarium (Vancouver, BC). All formulas were centrifuged for 30 minutes at 3,000 x g and 4°C to remove the lipid fraction. Human formulas (900 to 8,500 pg/mL) had greater ghrelin concentrations than pinniped formulas (600 to 3,000 pg/mL). Surprisingly, pinniped formula had a greater concentration of GH (26.02 ng/mL ± 4.73) compared with human formula (17.27 ng/mL ± 2.20). Increased ghrelin concentration in human formula is associated with increased intake rates of formula-fed infants. Reduced ghrelin concentrations in rehabilitation formulas could impact the urge to feed. Ghrelin and IGF-I additives to seal formulas may promote increased intake and increased growth rate of rehabilitated seal pups.
Acknowledgements
This research was supported by a Mazuri® Exotic Animal Nutrition Research Grant from Land O'Lakes, Inc. This research would not be possible without our collaborators at Mystic Aquarium, Mystic CT, The Marine Mammal Center, Sausalito CA, and Vancouver Aquarium, Vancouver BC.
* Presenting author
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