1. Caging: cotton rats are extremely excitable animals that are difficult to handle. For the convenience of the handler, cotton rats should be single-housed in polycarbonate rat cages, containing a stainless steel wire bar lid that snaps down tightly. Tekfresh rodent bedding is placed in the bottom of the cage for nesting. For environmental enrichment, a 10-cm piece of 3'' PVC pipe is placed in the cage. This pipe gives the animal a place to hide and helps to decrease the animal's stress.
2. Diet: the animals should be fed a standard rodent diet containing at least 18% protein (HSD Teklad 2018) and have free access to water. Because the cotton rats will likely experience shipping stress, food and water consumption should be closely monitored during acclimation. An acclimation period of at least 7 d is recommended.
3. Physical restraint: cotton rats have a strong fight-or-flight response and tend to bite when being caught and handled. During routine cage changing, it is recommended that the animal handler wear Kevlar gloves with latex-coated palms or some other type of thick glove for protection. The animal should not be handled by the tail, as degloving of the tail will occur. When removing the animal from the cage, the lid should be opened just enough for the handler to reach his/her hand into the cage. This will help to prevent the animal from escaping (11). The PVC pipe can be used to trap the animal for transfer into its new cage. The animal may be physically restrained by scruffing the skin over the shoulders and back tightly, while pushing the animal down with an appropriate amount of force.
Pushing the animal down too firmly may result in the cotton rat biting its tongue and bleeding from the mouth.
4. Short-term anesthetic restraint: cotton rats appear very stressed during catch-and-restraint procedures. CO2/O2 (USP 80/20 mix) can be used to lightly anesthetize the animals and facilitate physical restraint. This can be accomplished by pumping the CO2/O2 mixture into the animal's cage via a small tube until the animal loses consciousness. CO2 gas is heavier than air and tends to persist inside the cage for a long period of time; therefore, after the restraint procedure, the animal should be either placed into a new cage or returned to the original cage after the CO2 gas has dissipated or is fanned out.
5. Long-term anesthetic restraint: for certain procedures it is necessary to have the animal immobilized for an extended period. An anesthetic cocktail containing 30 mg/mL of ketamine and 10 mg/mL of xylazine in water for injection can be given at 0.1 mL/100 g body weight via intraperitoneal injection. The cotton rat should be scruff-restrained, as described above, and placed in dorsal recumbency with the head pointing downward for injection. A tuberculin syringe with a 25G x 5/8'' needle is used for injecting the anesthetic cocktail. The needle is inserted into the right lower quadrant of the abdomen at approximately a 45° angle. The syringe plunger should be pulled back slightly to ensure correct needle placement before the anesthetic is injected. If blood, feces, or urine is aspirated into the syringe, remove and discard the syringe and repeat the procedure using a new syringe of anesthetic cocktail. After injection, the animal should be placed into a cage without bedding until it loses consciousness. When the animal is fully anesthetized, Puralube petrolatum ophthalmic ointment must be placed in the animal's eyes to prevent corneal dryness and abrasions. During anesthetic recovery, place the cotton rat in the cage without bedding, and set it on a prewarmed circulating water blanket. An anesthetized animal's airway can become blocked if it aspirates bedding; therefore, cages without bedding are used for anesthesia and recovery. The animal can be returned to its original cage when it is ambulatory (the animal is mobile and has righting reflex).
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