Determining the mass of FL to provide for a 24 hr FL intake study
Background:
In replicating a study by Corwin 2004 in which we will offer FL in a variety of access schedules (instead of lard), it is necessary to measure 24 hour intake of the palatable food in a pre-test so that rats can be divided into experimental groups balanced according to the initial intake of palatable food and body weight. Since the palatable food we will test is Froot Loops (FL) it is important to determine the mass of FL to provide at the beginning of a 24 hr study so that amounts in excess of this can be provided initially to avoid complications associated with monitoring intake and providing additional FL as the amount consumed depletes the available supply.
Furthermore, it would be useful to know whether accurate measurements of FL consumption can be obtained while bedding remains in the cages during the 24 hr experiment.
Purpose:
To determine the quantity of FL to initially provide for a 24 hour study of FL intake.
Strategy:
Five male Sprague Dawley rats were selected from among those used previously for a restricted access to FL study conducted in the spring of 2007. These 5 rats were those which had recently consumed the largest quantities of FL in several recent pilot studies. Thus, by selecting these animals, we are likely to observe the upper limit of FL consumption, and we will be assured that the much younger, lighter rats to be used in the actual study will consume less FL than these old animals. An additional 2 animals of similar age with no prior history of exposure to FL were also included in this pilot study.
Procedure:
Seven male S-D non-food deprived rats were given 50+0.1 g of FL together with an unmeasured amount of rat chow in their lid hoppers at 11 am on 14 June 2007. The animals had been maintained since Jan 2007 on a 7am lights on/ 7 pm lights off schedule. Minimal new bedding was placed in the cages. Water was available ad libitum. Twenty-four hours later (at 11 am 15 June) FL were collected from the hoppers and bedding of each cage and 24 hr FL intake was calculated by subtracting the remaining mass of FL from the initial (50 g) mass. Rats were weight immediately after the FL measurements.
Results
Body mass of rat (g) / 24 hr cumulative FL intake (g)727 / 26.3
716 (no prior FL exposure) / 28.4
695 (no prior FL exposure) / 33.8
721 / 35.7
660 / 36.0
681 / 37.2
643 / 41.2
815 / 47.1
707 ± 53 g (Average ± SD) / 35.7 ± 6.6
Observations:
Many FL fell through the cage lids and were scattered in the bedding. Removing FL from bedding was rather tedious and time-consuming. Yellow and orange FLs are more difficult to see in the bedding. Because bedding absorbs urine effectively, the wetting of FL by urine is of little concern and had little impact on the mass of FL.
Since FL have an energy density of 3.8 kcal/g, these rats consumed 136 ± 25 kcal/g (mean ± SD) over 24 hours.
Conclusions:
Placing 50 g of FL in the hoppers should be more than adequate to determine 24 hr FL intake during our pre-test, the results of which will be used to separate 80 rats (currently 300-330 grams body mass) into 8 groups of 10 rats each balanced for body mass in food intake of the palatable food. It is likely that younger, less massive rats will require perhaps no more than 40 g of FL initially, but one should err on the side of excess.
Additional issues:
To reduce the likelihood that FL might remain lost in the bedding, one could use newspaper instead of bedding for the pre-test with the hope that newspaper would absorb urine and yet facilitate the retrieval of unconsumed FL. However, in a previous NASA-supported study at Wofford, hind limb unloaded rats were observed to shred folded newspaper used as bedding. Thus, even newspaper may not be ideal as a substitute.