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Prandial correlations measure the strength of the effects of between-meal interval length on the size of subsequent meals (pre-prandial) and vice versa (post-prandial) and provide insight into the control of food intake. In this paper we develop hypotheses about prandial correlations by using feeding behaviour data consisting of more than 300,000 meals that were recorded from at least 290 animals from each of six genotypes (four broiler lines, ducks and turkeys). The objectives of the study were to (i) obtain estimates of pre- and post-prandial correlations in the three species, (ii) quantify in probabilistic terms exactly how interval length affects meal size and vice versa and (iii) test whether prandial correlations were affected by selection intensity for growth in broilers. Pre-prandial correlations were statistically significant but interval length had almost no effect on meal size in ducks and turkeys and explained only 7–18% of the variation in meal size in broilers. Post-prandial correlations were higher than pre-prandial correlations and meal size explained between 8% and 42% of the variation in subsequent interval length. Selection intensity for growth did not systematically affect pre- or post-prandial correlations in broilers. The probability of animals starting a meal within the next 10 min ( P start ) remained close to zero for longer the larger the preceding meal was but meal size did not affect the rate of the rise in P start with time since the last meal. Similarly, the probability of animals ending a meal before consuming another g of feed ( P end ) was higher at the start of a meal the shorter the preceding interval length but the rate of the rise in P end with amount of food consumed was not affected by previous interval length. Analyses of effects of meal size on changes in P start and of interval length on changes in P end provide more information that is relevant for the structure of feeding behaviour than prandial correlations alone. Such analyses require an appropriate method to group feeding behaviour into meals and data sets of uniform feeding behaviour. A combination of the behavioural probabilities highlighted here with analyses of physiological changes occurring at the same time appears promising for the elucidation of the control of food intake.

Meals have long been considered relevant units of feeding behavior. Large data sets of feeding behavior of cattle, pigs, chickens, ducks, turkeys, dolphins, and rats were analyzed with the aims of 1) describing the temporal structure of feeding behavior and 2) developing appropriate methods for estimating meal criteria. Longer (between-meal) intervals were never distributed as the negative exponential assumed by traditional methods, such as log-survivorship analysis, but as a skewed Gaussian, which can be (almost) normalized by log-transformation of interval lengths. Log-transformation can also normalize frequency distributions of within-meal intervals. Meal criteria, i.e., the longest interval considered to occur within meals, can be estimated after fitting models consisting of Gaussian functions alone or of one Weibull and one or more Gaussian functions to the distribution of log-transformed interval lengths. Nonuniform data sets may require disaggregation before this can be achieved. Observations from all species were in conflict with assumptions of random behavior that underlie traditional methods for criteria estimation. Instead, the observed structure of feeding behavior is consistent with 1) a decrease in satiety associated with an increase in the probability of animals starting a meal with time since the last meal and 2) an increase in satiation associated with an increase in the probability of animals ending a meal with the amount of food already consumed. The novel methodology proposed here will avoid biased conclusions from analyses of feeding behavior associated with previous methods and, as demonstrated, can be applied across a range of species to address questions relevant to the control of food intake.

1. This study is the first to quantitatively compare the structure of feeding behaviour of broilers, ducks and turkeys as recorded by electronic feeders. It tests the hypothesis that this structure is so similar that the same models would be suitable to group the feeding behaviour of these species into meals. 2. Visits to electronic feeders were recorded from 3470 broilers, 3314 turkeys and 480 ducks. The frequency distributions of the length of short intervals between visits to feeders varied between species as a result of differences in the number of visits within a feeding bout, the frequency of re-visits to the same feeder and probably in the likelihood of birds drinking within meals. 3. The lengths of longer day-time intervals between visits to feeders were all log-normally distributed. Disaggregation of these intervals by feeding strategy (meal frequency) showed that the probability of birds starting to feed increased with time since feeding last in all species, which is consistent with the satiety concept. 4. Two methods, one based on fitting a truncated log-normal, function, the other on observed changes in the probability of birds starting to feed with time since last feeding, gave very similar meal criteria estimates. These ranged from 1050 to 1200 s in broilers, 1650 to 1725 s in ducks and 1250 to 1320 s in turkeys. 5. There were large between-species differences in the average number of daily meals, intake per meal, and feeding rate. Despite this variation, the overall structure of feeding behaviour of broilers, ducks and turkeys was so similar that the same models were suitable for application in all three species. This would allow for standardised analyses of feeding behaviour of different avian species kept in different husbandry systems.