Flavor variety enhances food acceptance in formula-fed infants.

BACKGROUND: Research in humans and animal models suggests that acceptance of solid foods by infants during weaning is enhanced by early experiences with flavor variety. OBJECTIVE: We tested the hypotheses that the acceptance of novel foods by formula-fed infants could be facilitated by providing the infants with a variety of flavors at the time when beikost is first introduced and that, contrary to medical lore, infants who had previously consumed fruit would be less likely to reject vegetables when first introduced than would infants without such an experience. DESIGN: The infants' acceptance of a novel vegetable (puréed carrot) and a novel meat (puréed chicken) was evaluated after a 9-d exposure period in 3 groups of infants, some of whom had previously consumed fruit. During the home-exposure period, one group was fed only carrots, the target vegetable; a second group was fed only potatoes, a vegetable that differed in flavor from carrots; and a third group was fed a variety of vegetables that did not include carrots. RESULTS: Infants fed either carrots or a variety of vegetables, but not those fed potatoes, ate significantly more of the carrots after the exposure period. Exposure to a variety of vegetables also facilitated the acceptance of the novel food, puréed chicken, and daily experience with fruit enhanced the infants' initial acceptance of carrots. CONCLUSION: These findings are the first experimental evidence to indicate that exposure to a variety of flavors enhances acceptance of novel foods in human infants.

Short-term influence of breastfeeding on the infants' interaction with the environment.

The present study tested the hypothesis that around the age of weaning, human infants are more interactive with their environment immediately after breastfeeding. To this aim, we assessed 4- to 6-month-old infants' responsiveness to a rotating, musical mobile before breastfeeding on one test day, and after breastfeeding on another. Thirteen infants, fitted with miniature movement detectors on both their left leg and wrist, were videotaped for 4 consecutive min during which the mobile was alternately switched on and off in 1-min intervals. Although the infants showed no significant differences in limb activity as a function of the timing of a breastfeed, they looked at the mobile significantly longer when tested after breastfeeding. This finding suggests that breastfeeding has a substantial effect on 4- to 6-month-old infants' attentiveness to and interaction with their environment.

Acute, early thermal experience alters weaning onset in rats.

We hypothesized that first ingestion of solid food (weaning onset) would be accelerated in young rats with advanced thermoregulatory development. To manipulate the pups' thermoregulatory development, we exposed rat pups, but not their dams, to a Cold (10 degrees C), Moderate (21 degrees C), or Warm (31 degrees C) ambience for 2 h/day from postnatal Day 2-14, expecting that early exposure to cooler temperatures would accelerate development of thermoregulatory capabilities and thus accelerate nest egression as well as onset of feeding. Contrary to expectation, cold exposure was associated with a profile of developmental delays in both growth and maturation. Pups in the Cold condition began feeding later than pups with Moderate or Warm thermal experiences. We then evaluated thermoregulatory status (mechanisms for heat production and temperature conservation) on Day 15-16 (just prior to weaning onset). Thermogenesis, measured by oxygen consumption, was unaltered by the thermal manipulation. In contrast, pelage development (insulation) was altered. Pups in the Warm condition had greater fur density and an increased frequency of longer hairs relative to pups in the Cold condition. Although the developmental response to early cold exposure was in the direction opposite to our predictions, the hypothesized relation of thermoregulatory development to weaning onset was supported: Thermoregulatory status correlated with weaning onset.

Effects of exposure to alcohol in mother's milk on infant sleep.

OBJECTIVE: To test the hypothesis that exposure to alcohol in breast milk affects infants' sleep and activity levels in the short term. METHODS: Thirteen lactating women and their infants were tested on 2 days, separated by an interval of 1 week. On each testing day, the mother expressed 100 mL of milk, while a small, computerized movement detector called an actigraph was placed on the infant's left leg to monitor sleep and activity patterning. After the actigraph had been in place for approximately 15 minutes, the infants ingested their mother's breast milk flavored with alcohol (32 mg) on one testing day and breast milk alone on the other. The infants' behaviors were monitored for the next 3.5 hours. RESULTS: The infants spent significantly less time sleeping during the 3.5 hours after consuming the alcohol-flavored milk (78.2 minutes compared with 56.8 minutes after feeding alcohol in breast milk). This reduction was apparently attributable to a shortening in the longest sleeping bout (34.5 compared with 56.7 minutes for sleeping after breast milk alone) and the amount of time spent in active sleep (25.8 minutes compared with 44.2 minutes after breast milk alone); the decrease in active sleep was observed in all but 2 of the 13 infants tested. CONCLUSIONS: Although the mechanisms underlying the reduction in sleep remain to be elucidated, this study shows that short-term exposure to small amounts of alcohol in breast milk produces distinctive changes in the infant's sleep-wake patterning.

Postsuckling behavioral arousal in weanling rats (Rattus norvegicus).

Twenty-day-old litters and their dams were observed in seminatural habitats consisting of a nest compartment and adjacent open field that contained powdered rat chow. It was found that pups displayed marked bursts of activity after suckling. Independent feeding reliably followed nursing bout termination (Experiment 1). Nipple withdrawal, with or without milk transfer, induced behavioral arousal whereas withdrawal of thermotactile and conspecific odor cues did not (Experiments 2-3). Increased thermogenesis was observed following milk transfer (Experiment 4). Finally, preweanling pups (10- to 12-day-olds) also displayed postsuckling arousal within the confines of the nest; full locomotor expression of this arousal was not evident until weaning age (Experiment 5). It was concluded that postsuckling arousal in weanlings functions to stimulate activities performed away from the nest and suckling, propelling pups into the field where feeding begins.

Environmental temperature modulates onset of independent feeding: warmer is sooner.

Individual dams and their litters were observed from Days 14-22 in a seminatural environment consisting of a nestbox attached to a larger, open field in which powdered chow was available. Ambient temperature in the field was either warm (30 degrees C), moderate (21 degrees C), or cold (10 degrees C); nest temperature was always moderate. Behavior was monitored 12 hr/day by time-lapse video recording. The pups' egressions into the field and onset of independent feeding were temperature-related: Weaning was earliest in the warmth and increasingly late with decreasing ambient temperature. Among subjects in the cold condition, there was a positive correlation between duration in the field and duration feeding. Pup growth was unaffected by the temperature regimes. Environmental temperature has emerged as a determinant for early nest egressions and weaning onset.

Differential influence of adult and juvenile conspecifics on feeding by weanling rats (Rattus norvegicus): a size-related explanation.

Weanling Sprague Dawley rat pups (Rattus norvegicus) selected between 2 safe palatable diets in concordance with the preferences of either an adult or a juvenile conspecific model (Experiment 1). Nevertheless, weanlings chose to feed more in the vicinity of an adult than in the vicinity of a juvenile, thus fulfilling the prediction of an adaptive feeding strategy (Experiment 2). The weanlings' bias for feeding in the vicinity of an adult was eliminated by increasing the magnitude of pup stimulus to 3 pups (Experiment 3). Thus, weanlings do not possess a specialization rendering them more sensitive to adults than to pups as models for diet selection. By responding to stimulus magnitude, weanlings are more likely to feed with adult conspecifics, choose foods used by them, and derive the benefits correlated with the adults' successful feeding habits.