PubMed Health⌕ Search

Biomedical subjects

G H Collier

Publications and source records attributed to G H Collier.

At least 19 recordsLinked to original sources
PubMed1998

The timing of food availability affects growth in chicks.

Three experiments challenged the ability of domestic chicks to grow normally by differentially restricting when and for how long food was available. In Experiments 1 and 2, food was available for six 1-hr, three 2-hr, two 3-hr, or one 6-hr (a.m., p.m.) periods/day over the first 3 posthatch weeks. Control groups received continuous access to food. In Experiment 3, different amounts of light surrounded the 6-hr feeding period. In Experiments 2 and 3, chicks composed their own diets from separate sources high in protein or carbohydrate. Except for the single 6-hr meal preceding dark, large meals at other times of day impaired growth--primarily because chicks consumed insufficient dietary protein and ate less earlier in the light phase. We conclude that both the amount eaten and the proportion of the diet consumed as protein at given times of the day are phylogenetically acquired strategies that fit the omnivorous, diurnal chicken to its niche, independent of its momentary requirements, and appear early in development.

Analysis of Variance↗
PubMed1995

Procurement time as a determinant of meal frequency and meal duration.

Foraging involves the expenditure of both time and effort in the acquisition of food; animals typically modify their meal patterns so as to reduce these expenditures or costs. The contribution of time, as compared with effort, to the overall cost perceived by an animal is not known. We investigated the effect of foraging time as a cost independent of effort by measuring the meal patterns of rats living in a laboratory foraging simulation in which they earned all their daily intake. They pressed a bar once to initiate an interval (procurement interval) leading to the presentation of a large cup of food from which they could eat a meal of any size. As the length of the interval increased from 1 s to 46 hr, meal frequency decreased regularly. Meal size increased in a compensatory fashion, and total daily intake was conserved through an interval of 23 hr. The changes in meal frequency occurred because of changes in the rat's latency to bar press after each meal. The functions relating meal frequency and size to the procurement interval were of the same shape as those seen when cost is the completion of a bar-press requirement, which entails the expenditure of both effort and time. When the bar-press requirement was increased to 10, meal frequency was reduced, but time and effort did not appear to simply add together in the rat's perception of cost. These data reveal that time is preceived to be a cost by rats foraging in this laboratory environment. These results suggest that the time parameters of foraging are different from those of consumption.

Animals↗
PubMed1990

Activity patterns in rats (Rattus norvegicus) as a function of the cost of access to four resources.

Patterns of eating, drinking, wheel running, and nesting were recorded in 2 experiments in which rats (Rattus norvegicus) lived in a laboratory environment that provided food, water, a running wheel, and a nest box. Access to each resource was contingent on the completion of a fixed ratio of bar presses and once earned remained available until the resource was not used for 10 consecutive min. In all cases an increase in the access price of a resource produced a decrease in the frequency with which the resource was accessed. This reduction in bout frequency was countered by an increase in bout size, which was compensatory for eating and nearly so for drinking, but which was only partially compensatory for wheel running. Nest bout size did not change significantly as nest price increased. The bout patterns of these 4 activities changed independently of one another, and the probabilities of behavioral transitions did not indicate strong links between any pairs of activities.

Animals↗
PubMed1989

The effect of dexamethasone-21-acetate on meal size, meal frequency and macronutrient self-selection in rats.

In Experiment 1, the measurement of 24-hour food intake in two rats showed that treatment with dexamethasone-21-acetate (DEX) (0.5 mg/kg IP) produced a decrease in body weight which was at least partially due to a decrease in food intake (both meal frequency and meal size). In Experiment 2, the daily intake of three macronutrient sources was measured. These data showed that treatment with DEX (0.5 and 1.0 mg/kg IP) led to an acute increase in protein intake, a sustained decrease in fat intake and no change in carbohydrate consumption. We suggest that this change in macronutrient selection may be an adaptive response which serves to ameliorate some of the effects of DEX treatment.

Animals↗
PubMed1989

Ambient temperature and food costs: effects on behavior patterns in rats.

Eating, drinking, wheel running, and nesting were recorded continuously in animals living in cages where they foraged for and consumed food by completing operant bar-press requirements. The ambient temperature was either 24 or 0 degrees C. Two food costs, that of initiating meals and that of pellets within meals, were separately manipulated at each temperature. Compared with room temperature, the cold temperature produced a doubling of food and water intake and a greater than twofold increase in nesting time each day. Running behavior was not altered. Regardless of temperature, the cost of initiating meals influenced the frequency and size of meals but did not affect total food intake or time spent feeding, and this cost had no effect on any other activity. As the cost of pellets within meals increased, the time spent feeding increased and there was a decline in daily food intake. The change in intake was greater at the cold temperature because in the cold the rats did not increase daily feeding time sufficiently to maintain intake as pellet cost increased. Such an increase in feeding time would have required that less time be spent in one of the other activities.

Acclimatization↗
PubMed1988

Changes in macronutrient selection as a function of dietary tryptophan.

It has been hypothesized that the serotonergic system is involved in the regulation of carbohydrate and/or protein intake. Tests of this hypothesis using added dietary tryptophan and diets varying in the ratio of carbohydrate/protein resulted in depressed intakes of high carbohydrate/low protein diets, elevated intakes of low carbohydrate/high protein diets, and a reduction of total caloric intake. The present studies gave rats increased options for adjusting to added tryptophan by providing them with separate sources of protein, carbohydrate, and fat. The results showed the expected decrease in carbohydrate intake, but also increases in fat intake and, to a lesser extent, protein intake. Total caloric intake was conserved. Hypothalamic concentrations of serotonin and 5-hydroxyindole acetic acid indicated increased activity of the serotonergic system. These results lend support to serotonin's involvement in nutrient selection, in that carbohydrate consumption decreased in response to tryptophan loading, but indicate that other nutrients may also be affected. Given the option of altering fat intake, the animals maintained a constant caloric intake despite the reduction of carbohydrate consumption.

Animals↗
PubMed1987

Caloric regulation and patterns of food choice in a patchy environment: the value and cost of alternative foods.

Rats in a laboratory foraging paradigm had 24-hr-per-day access to a feeder where they could search, by completing a fixed number of bar presses, for an opportunity to eat one of a pair of foods differing in caloric density (2.5, 3, 3.5, or 4 kcal/g) and, in Experiment 2, the price of food pellets (10 to 50 bar presses per pellet). The rats could either accept the opportunity, and eat a meal, or reject it in favor of further search. Daily caloric intake was relatively constant. The rats always included both foods in their diet, but, for any particular food, the degree of inclusion in the diet and of acceptance of meal opportunities, the meal size, and the rate of eating were all functions not only of the price and caloric value of that food but also of the price and value of the alternately-available food. The patterns of intake for one food relative to those for the other available food were strongly correlated with the relative rate of calorie intake during consumption of that food compared to the other. Although the rats appeared to be sensitive to the local rates of calorie flow, they did not maximize daily calories consumed per time spent feeding.

Animal Husbandry↗
PubMed1986

Changes in rats' meal patterns as a function of the caloric density of the diet.

Rats in a laboratory foraging paradigm were offered each of four diets which differed in caloric density, and intakes, meal frequencies, meal sizes, and eating rates were monitored. The rats maintained a constant daily caloric intake by eating more frequent, larger meals of the lower density foods. However, caloric meal size was not regulated, and significant correlations between meal size and the length of the post-meal interval were rarely found. The 24-hour pattern of calorie intake was the same regardless of diet. Higher-calorie foods were consumed at a faster rate within meals than were lower-calorie foods. The feeding patterns observed suggest that caloric intake may be regulated over a time frame of several meals rather than on a meal-to-meal basis.

Adaptation, Physiological↗
PubMed1986

The economics of the law of effect.

A corollary of the law of effect predicts that the larger the reinforcement, the greater the rate of responding. However, an animal must eat more small portions than large portions to obtain the same daily intake, and one would predict, therefore, that when eating smaller portions an efficient animal would eat less (conserving time and energy) and/or respond faster (conserving time). The latter of these predictions was supported by the present experiments with free-feeding rats for which portion size (pellet size or duration of feeder presentation) and portion price within meals were varied. Response rate was a function of the unit price (responses/g) of food: Rats responded faster when portions were smaller or when prices were higher. Meal size and frequency were relatively unaffected by unit price, but were influenced by the price of meal initiation. The results are discussed in relation to the economic differences between traditional operant and free-feeding paradigms and to both traditional and more recent formulations of the law of effect.

Animals↗
PubMed1985

Satiety: an ecological perspective.

The frequency and size of meals in freely feeding animals vary as a function of the economic structure of the animals' niche and their habitat. This paper reviews some of the evidence supporting this proposition. When the cost of access to a meal increases, the frequency of meals decreases and their size increases compensatorily. Similarly, increasing the caloric density of a meal results in a decrease in both meal frequency and size. When foraging animals encounter opportunities to procure meals that differ in cost or in benefit, they almost always procure low-cost or high-benefit meals. The frequency with which they procure high-cost or low-benefit meals is a function of the magnitude of the difference between either the costs or the benefits of the meals they had an opportunity to procure. To feed optimally an animal must minimize the sum of the costs of foraging, consumption, and utilization and maximize the sum of benefits. To accomplish this, an animal must integrate information from its niche, its habitat, the process of ingestion, postingestive consequences, and its metabolic state. Feedback from both the consequences of ingestion and the metabolic state probably acts indirectly to provide information rather than directly as a satiety stimulus.

Animals↗
PubMed1984

Self-selection and the obese Zucker rat: the effect of dietary fat dilution.

Adult female lean and obese Zucker rats were allowed to compose their own diets by giving them access to three macronutrient sources. After a baseline period, the fat source was serially diluted. In all, eight concentrations of fat were used. Dilution of the fat source promoted significant increases in the intake of fat by both lean and obese rats. The increased intake of fat was not simply compensatory in nature, but rather represented significant increases in fat consumption. These results suggest that the reported increased appetite for fat of the obese rat is not a unique trait of that genotype. Further, results from this experiment demonstrate that caloric and protein regulation mechanisms may not be controlling the intake of obese and lean rats as precisely as once believed.

Animals↗
PubMed1984

Purified diets: some cautions about casein.

Growth and intake of weanling rats on five casein-based purified diets and matched cereal-based diets were compared. The results support Lát's conjecture that the failure of animals to exhibit normal growth on some purified diets may be attributed to their failure to consume sufficient casein. Given a choice, the rats consumed both types of food, composing a diet in which the ratio of purified to cereal-based diet was 2:1, and they grew normally. Although the growth-promoting characteristics of caseins from different sources varied, the preference ratio between casein- and cereal-based diets was the same with one exception: a reduced preference for purified diet was shown by animals who had previously experienced subnormal growth for an extended period of time on a purified diet. These results show that all caseins are not equivalent in their growth-promoting properties. Further, they show that rats are exquisitely sensitive to the nutritional properties of their diets and, given the opportunity, can compose a diet which yields normal growth.

Animal Feed↗
PubMed1984

Effects of dietary nutrients and foraging costs on meal patterns of rats.

Rats were fed either a cereal-based or a purified casein-based diet in a foraging paradigm in which the costs of procurement and consumption were varied. The group offered the cereal-based diet consumed about 10% more calories than the group offered the casein-based diet, but both groups grew at the same rate. The intake of a control group offered a choice between the two diets was approximately 80% from the casein diet, and the growth of this group did not differ from that of the experimental groups. Variations in the cost of procurement and the cost of consumption affected the patterning of meals differentially for the two diets: changes in meal patterns tended to control the time and/or energy spent feeding. These results show that (1) meal patterns in the foraging paradigm are sensitive to subtle differences in diets, and (2) the amount of diet consumed (acceptance) and the choice between diets (preference) are determined by the economics of feeding and the nutritive quality of the foods, as well as by their palatability.

Animal Feed↗
PubMed1983

Self-starvation: a problem of overriding the satiety signal?

Rats housed in either activity wheels or standard laboratory cages received access to food either ad lib or for one 60-min, two 30-min, or four 15-min periods per day. Imposition of restricted feeding schedules led to reductions in food intake and body weight which were greater for animals with access to activity wheels. Increases in activity reflected the percent of body weight loss, which varied directly with frequency of food access. Subsequent recovery of intake was facilitated by partitioning total feeding time into briefer but more frequent periods. In the most extreme frequency-of-access condition, animals with access to running wheels failed to recover from the reduction of intake incurred by imposition of the restricted feeding schedule, even though their total feeding time was the same as that of animals that did recover. These data indicate that self-starvation is not induced by activity per se but results from a general failure to recover intake which, in turn, results from a failure to override the satiety signal within a meal.

Animals↗
PubMed1983

A cost-benefit analysis of nocturnal feeding in the rat.

Rats are nocturnal feeders. The present results show that when either the cost of procuring a meal or the cost of consuming it increases differentially in the dark relative to the light, rats shift their feeding activity to the light phase of the light/dark cycle. These results suggest that some of the same factors that presumably provided the selection pressure for nocturnal feeding in the phylogeny of the rat are still capable of modifying its current patterns of feeding.

Adaptation, Physiological↗
PubMed1982

The economics of food choice in chicks.

Growing chicks offered diets containing either surfeit or inadequate protein in the day but adequate protein at night adopted a pattern of nocturnal feeding but did not eliminate diurnal meals. Their weight gain surpassed that of corresponding dietary controls who received continuous access to surfeit or inadequate protein but was less than that of chicks with continuous access to a standard diet. Chicks receiving the standard diet at night with no food available in the light phase also grew but did so at a slower rate than the diurnally feeding control group. The shift in feeding patterns was not accompanied by a shift in body temperature, nor was nocturnal antipredator behavior, characterized by sustained motoric inhibition, disrupted by nocturnal feeding. These data demonstrate that feeding specializations which have been selected over a species' evolutionary history are not rigidly fixed but can be modified by the economic relations in the current habitat.

Animal Feed↗