This article is from the July/Aug. 1995 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M.

In the May/June 1995 newsletter there were a number of comments concerning freezing as a method of euthanasia for rodents. Freezing is not considered to be a humane method of euthanasia for rodents other than for neonates (pinkies). The most humane method outside of anesthetic overdose is carbon dioxide from either gas or dry ice (the animal is not in direct contact with the dry ice). The carbon dioxide is painless and considered humane by the American Veterinary Medical Association’s Panel on Euthanasia. Neonates are often resistant to carbon dioxide and are asphyxiated with the gas and then put in the freezer for humane euthanasia. If you take your animal to your veterinarian for euthanasia, ask them to use methoxyflurane anesthetic gas to render the animal unconscious before administering the euthanasia agent. The euthanasia solutions that most veterinarians have are intended to be given directly into a vein. When given by intraperitoneal (abdominal) injection it is painful to the animal because of the pH of the solution. Intraperitoneal injection with an overdose (120 mg/kg) of the anesthetic form of Na Pentobarbital (by a veterinarian experienced with rodents) is not painful for the animal and is considered humane. I do not recommend chloroform as this is harmful to humans by direct contact or inhalation.

Before I graduated from veterinary school, my mother had the misfortune of taking her sick, aged rat to an inexperienced, poor-quality veterinarian for euthanasia. My mother wanted to be present, and she wanted to take the remains for burial. This insensitive clod, had the poor taste to inquire why my mother was so upset about the animal, since it was “just a rat.” He then tried to administer some euthanasia solution directly into the heart of my mother’s old, extremely nice, Siamese rat. He didn’t know what he was doing and as a result, the rat suffered a painful and stressful death. As a result of this my mother will never own another rat.

Intracardiac injection of euthanasia solution is not considered humane on conscious animals. Make sure that you discuss the procedure with your veterinarian before you take your pet rodents in for euthanasia as not all veterinarians are experienced with humane euthanasia in rodents. These type of situations can be avoided and no one should have to go through this with their pets.

In the March issue of Contemporary Topics of the American Association for Laboratory Animal Science, there was a paper on “Eradication of Pinworms from Rats Using Ivermectin in the Drinking Water” by Kerrick, GP et al. In summary the report details the use of 10 mg Ivermectin (Eqvalan brand) per 16 ounces of water daily for three consecutive days for three weeks as an effective treatment. Since the ivermectin is sensitive to light, it has to be changed daily. Even though filter top cages were recommended as part of the process, I think that it would be worth a try in a small colony or pet situation. You have to use Eqvalan since other products are not water soluble. For a gallon of water you would need 8 ml of Eqvalan. I spoke with a veterinarian at the drug manufacturer and to date there is no known resistance to this product by parasites that are sensitive to it.

There is a company in California that will directly formulate Ivermectin into a rodent block diet. There is a minimum milling requirement of 300 pounds. The feed would be shipped in 50 pound bags. They recommend using the feed up within 2 months for maximum effectiveness. Remember, ivermectin is also effective against mites.

Another product that has been used for treatment of pinworms is Fenbendazole at a dose of 50 parts per million added to the feed for 1–6 weeks (Harkeness and Wagner). There are two veterinary products both called Panacure. The granular form is supplied in 1 pound containers at a concentration of 222 mg/g and you would need to add 10 grams to every 100 pounds of feed. The liquid suspension is supplied in 1 liter units at a 10% concentration (100 mg/ml) and you would need to add 23 ml for every 100 pounds of feed.

Many people who have used only piperazine in the past now have pinworms resistant to this product. It is best to rotate with the use of different products to avoid developing a resistant population of pinworms. The recommended dose for Piperazine Citrate is 3 grams per liter of water. Note: For other forms of Piperazine (adapate, monohydrate, etc.) the concentration is different and a different amount would be needed.

A paper of relevance to rats and mice from the journal, Laboratory Animal Science Vol 45:1 Feb ’95, “Plasma and lung concentrations of oxytetracycline after its intramuscular administration in rats” by Baxter and McKellar. In summary: Tetracycline and oxytetracycline have been recommended for the treatment of murine respiratory tract mycoplasma infections caused by M. Pulmonis. These drugs act by dose-dependent bacteriostatic activity (inhibit growth) and act by inhibiting protein synthesis in susceptible organisms. In rats they have been administered orally, intravenously, and intramuscularily. Because of their small size, intravenous dosing is impractical. The use of tetracycline in the drinking water has been shown to absorb poorly into the body. The drug may be bound to food in the digestive tract and account for the poor bioavailability of the drug. When large amounts are used in the drinking water, the animal may be further debilitated since it makes the water taste so bad that less is consumed, even when sugar is added. In this paper the recommend intramuscular injection 10 mg/kg of oxytetracycline once every 24 hours. They did caution that necrotic lesions could result at the injection site with some formulations of oxytetracycline. They used 20 gauge needles and Terramycin Q50 (oxytetracycline 50 mg/ml, Pfizer Ltd.).

I am sorry to hear that more people have been having problems with SDA virus. It is crucial to quarantine new animals and not breed for 2 months. Supportive care to extremely ill animals can help with secondary problems, but the animal has to clear the virus itself.

An update on enrofloxacin, Baytril. I contacted the drug manufacturer regarding the use of the injectable product in rodents. The effective dose is 2.5 mg/kg body weight when given I.M. [intramuscular]. Since this product has to have a low Ph and some discomfort is experienced when it is given, I asked if it had good bioavailability when given orally. He said that it would probably be okay, and that they gave up to 500 mg/kg with out any side effects. He also said that it was the peak blood levels that was important rather than the duration of the drug in the body. Since it is cleared in about 8 hours, I have used 25 mg/kg of the injectable product orally twice a day in sick mice with out incident. Since this is an expensive antibiotic, I would only use this in extreme cases where other antibiotics are not working.

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