Milk intakes of genetically obese (ob/ob) and lean mouse pups differ with enhanced milk supply

Although obese (C57Bl/6J, ob/ob) pups have greater avidity for nonnutritive suckling than leans as early as 15 days postpartum, previous research has not found differences in milk intake between ob/ob and lean mice during the preweaning period. Because ob/ob pups suckle longer than leans, their perseveration should enhance their opportunity to ingest milk if (a) maternal milk supply is not limited and (b) longer sucking durations reflect increased pup willingness to ingest milk. Accordingly, the present study was designed to evaluate the milk intake of ob/ob and lean pups when they had access to an enhanced supply of maternal milk. Intact litters of pups, from heterozygous lean (ob/+) parents, were randomly assigned to be tested at either 6, 12, or 18 days. Pups were neither dam- nor milk-deprived before being cross-fostered successively to milk-replete surrogate dams for 60 min each. Obese pups showed a greater percentage body weight gain (the index of milk intake) than leans did, with younger pups showing larger increments than 18-day-olds. Although early adiposity in ob/ob pups may not rely on increased intake in the single-dam, nest situation, these data emphasize an early predisposition to overeating in this mutant.