Module VI Flashcards
- Describe different types of diets for laboratory animals and how they are constructed to meet the dietary requirements for the animals
Natural ingredient diet (chow) - can be whole grains, such as corn, barley, and wheat, mill by-products, such as bran, high protein meals such as soybean, fish or casein, and bone meal is often used as a mineral source.
● Advantages of a natural ingredient diet is that it is cheap, the animals like it, and it is nutritious.
● The disadvantages in relation to using it for experimental animals is that there is variation between batches of the same diet from the same producer, and even higher variation between for instance rodent diets from different producers. In the natural ingredient diet it is not possible to remove a single substance without removing major fractions of the diet. “Natural ingredients” may vary between countries (e.g. NA grows more corn and wheat, while Europe grows more wheat and barley)
Purified diets - based upon synthetic compounds. Protein source is casein or even the simple amino acids. Carbohydrates are sucrose and starch, the fibre can be cellulose and oils can be added as fat source. Various mineral and vitamin mixtures are added to it like in the natural ingredients list but in amounts to fulfil the entire needs of the animals.
● Advantages: highly standardized with low variation between batches, and you can decide for experimental purposes to make it devoid of single components compared to a test diet.
● Disadvantages: animals do not like them as much as the natural ingredient diets, they are far more expensive to use, and they may lack biologically active compounds of importance for the model.
In the fat fraction, we have the essential fatty acids linoleic, linolenic and arachidonic acid, which should comprise 1 - 1.5 % of the metabolizable energy.
In the protein fraction, must be the amino acids Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine, and for each of these there are some defined needs.
Macrominerals, which are minerals which should be supplied with more than 100 milligrams per day, are calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur, while microminerals, which can be supplied with less than 100 milligrams per day, are iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc and molybdenum.
Vitamins are organic molecules, which are not covered by the terms essential fatty or amino acids or minerals, but which the animal still needs on a daily basis. Some of these are fat soluble. Those are A, D, E and K, for which there are specific daily minimum needs. Others are water soluble. Those are primarily the B vitamins, for which some daily needs also can be defined. Vitamin C is only essential and therefore only considered a vitamin in guinea pigs and primates, while other animal species can synthesize it themselves.
- Describe how you would use specific diets for specific studies, how you would order them, and how you would store them
Growing animals need more energy and more protein than adult animals, and pregnant or lactating animals need energy for producing fetuses and milk. Therefore, they differ in food intake, and specific diets should be chosen according to that.
Diet can be ordered from online diet producers. Some of the diet producers work with a closed formula, that means they tell you the level of nutrients but not the components. Others work with an open formula and tell you exactly which ingredients they mixed into the diet. The diet will be delivered from the producer in bags or buckets: large for the natural ingredients diet, while normally a bit smaller for the purified diets. These must be stored in a cool, dry, rodent-free space. It is important to check that the correct diet has been received and to check and note the batch number. It should be noted precisely which batch is fed to which animals and when, and one study should be fed the same batch throughout the study. If it is not possible to feed an entire study the same batch within the lifetime of the diet, the diet should be frozen and the needed amounts for feeding the animals should be thawed every week.
The diet producer will deliver a batch control. This is mainly to document that the level of key nutrients is within the promised range, and that specific chemical residues and pathogenic bacteria are not present.
Sterilization of diet can be done in an autoclave or by gamma irradiation. Autoclaving can affect the nutrient quality, so the diet needs to be designed for autoclaving. An irradiated diet requires special facilities and you buy your diet irradiated. It is a very effective way of sterilizing the diet. Your diet will then be delivered in two bags. An outer bag, that is used for transportation and then a totally sterile inner bag, which has not been in contact with anything in the environment. This is the diet which will be used for gnotobiotic isolators.
Ad Libitum Feeding - simply make sure that there is always food in the food hopper.
Restricted Feeding - give the animals exactly the food they need to secure the intake according to their daily nutrient requirements (prevent animals from becoming overweight, especially rabbits). Survival is highest for the rats eating the least and that’s also the case for many diseases. Ad libitum fed animals have a higher disease rate than animals fed restrictedly.
Pair Feeding - Get two groups which eat exactly the same amount by registering the food intake in the group, which eats the most, and then supply the other group with exactly the same amount of food.
Fasting of mice before a procedure may be necessary but this can cause significant changes in body temperature, corticosterone, body weight. Fasting may make rodents turn into a state of torpor; that means they reduce their metabolism and body temperature due to the lack of food, some sort of pseudo hibernation. Correct way to fast rodents is to remove the diet when the lights turn on in the stables, and return it after six hours.
Oral gavage - precise dosing through a gastric tube, you must take into consideration that there will be no oral digestion, and data may be less translational compared to humans, such as slower peaks in glucose and insulin. However, the argument for doing this is that it is more precise and individual than dosing through the diet or drinking water.
