Consistency of meal patterns in laboratory rats.

Meal pattern measures (e.g., bout length and bout number) provide a detailed description of the elements of ingestion, and as a result they are theoretically more sensitive to experimental manipulation than simple measurements of total consumption over a fixed time period. For this reason, meal pattern measures are often used as a way to infer how rodents respond to tastants or how pharmacological or surgical treatments modify ingestive behavior. This approach relies on the assumption that under normal conditions, the meal patterns of individual rats are consistent across consecutive light-dark (L-D) cycles. If these patterns are inconsistent, then experimental designs involving meal patterns would have limited power, and thus require relatively large sample sizes. The present study critically evaluates the consistency assumption in Sprague-Dawley and Fisher-344 rats by monitoring meal patterns over 10 consecutive L-D cycles. For each rat, the following feeding and drinking measures were determined: total daily intake, duration of night bouts, number of night bouts, and number of licks per night bout. The analysis excluded daytime ingestive measures owing to their infrequent occurrence. Ingestive measures were highly consistent across time in all Sprague-Dawleys, but in only a minority of the Fisher-344s. The distribution of feeding and drinking activity throughout each night was also determined in the same rats. Whereas Sprague-Dawleys displayed lights-off and lights-on peaks of ingestive activity, only a minority of Fisher-344s displayed a consistent lights-on peak of ingestive activity. It is concluded that rat strains can differ with respect to the consistency of meal patterning, and that such strain differences should be considered in future comparative studies of meal patterns in rats.