When an influence of various toxic substances or prospective medicines on an organism is estimated, the concentration of the substance in question in tissues must be evaluated. Therefore, the masses of internal organs must be measured, so if they will be excessive, it will distort the results of the experiment. The influence of different feed types and different daily amounts of feed on the body mass dynamic in mice was estimated. In the first experiment animals were divided into four groups: two of them were given combined feed, and another two were given fresh feed. In each pair of groups in one of them mice were given the daily standard amount of the feed (1st and 3rd groups), and in another group animals were given unlimited access to the feed (2nd and 4th groups). In the second experiment two groups of mice were distinguished: one group was given combined feed, and another was given fresh feed. The limited daily standard amount of feed was used in the second experiment: it was ¾ of the daily standard amount of the feed. Feed type had an influence on the mice’ body mass dynamic: mice that were fed combined feed gained weight quicker than animals that were fed fresh feed. No difference in weight gain was found between mice that were given the daily standard amount of the feed and mice that were given unlimited access to the feed. So the daily standard amount of the feed that is included in the recommendations on feeding of laboratory animals is excessive in comparison with the real daily feed consumption. Animals gained weight with the limited daily standard amount of feed, so the daily amount reduced to ¾ of the standard remains bigger than (or equal to) the real daily feed consumption. And the final body mass was similar between the groups of combined feed and fresh feed: it can be the evidence of a lack of excessive weight in mice. So, when an experiment with two-months animals or older is being designed, with any feed type the daily amount of it reduced in comparison to the recommended daily standard amount must be chosen for a decrease of probability of excessive weight gain.
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