This article is from the Rat Health Care booklet. Order one today! Check out the info at Rat Books
by Debbie “The Rat Lady” Ducommun
Note about wild rats: Please see the info at the bottom of the page.
Baby rats are about 1 ¼ inches (3.2 cm) long at birth, and are pink and hairless. House mice are only about ¼-inch (0.64 cm) long at birth. Deer mice, which is a common wild species found as orphans, are about one inch (2.54 cm), long at birth. All of these species start getting fur at about one week of age. At two weeks old their eyes open and they have a very short coat of fur. At three weeks of age their fur gets fluffy. At about four weeks old their fur flattens down again. From this point on, their appearance doesn’t change much, just their size. It is normal for infant rodents to be uncoordinated because their nervous system isn’t completely developed. At three weeks they start to be more and more coordinated.
It’s very difficult to hand raise a baby rat (or mouse) who is less than a week old (a pinkie who doesn’t have any hair yet). The best option is to find a nursing rat to serve as a foster mother. As long as the babies are about the same age as her own, mother rats are almost always willing to adopt orphans. The best way to locate a foster mother is to contact local breeders, pet shops, or rat rescues.
The best way to introduce new babies to a foster mom is to take the mom out of the cage, then put the orphans in with her own babies, rubbing them all together to get the scent of her own babies on the orphans.
If a foster mother isn’t available, the only alternative to save an orphan is to raise him yourself. When attempting to raise an infant rat, there are three elements to consider: warmth, hygiene, and diet.
The best place to keep an orphaned rat before his eyes open is in a small cardboard box on a piece of felt or fleece large enough to also form a blanket over the baby. (Felt has no threads that can get wrapped around the baby’s legs.) Infant rats can climb better than you might think. Be sure to use a box at least 6" deep, or cover the box so the baby can’t climb out.
Until their fur becomes fluffy (at about 3 weeks of age), baby rats can’t keep themselves warm and you must give them supplemental heat. You can supply warmth for the baby with a heating pad (the best option, but be sure it doesn’t have an automatic shut-off feature), a light bulb, or something like a hot water bottle or an product designed to be heated in the microwave. Of course, a hot water bottle or microwaved object will need to be reheated periodically. The important thing is to keep a thermometer next to the baby so you know exactly what temperature he is experiencing. Use a small weather thermometer, not a medical thermometer, as the latter can’t record drops in temperature. Keep the temperature around 100-102 degrees F (37.78-38.89 C). Higher temperatures can be fatal. But if the baby gets too cold, that too can be fatal.
Use heating pads with extreme care as they can get very hot. Use on the low setting only and place only one end of the box on the pad so the baby can crawl away from the heat if necessary. You may even have to put a towel between the pad and the box to keep him from getting too hot. At two weeks of age you can start gradually reducing the temperature. Light bulbs can also get very hot. Make sure the light bulb is not too close to the baby because it can actually cook him. You absolutely must use a thermometer if you use a light bulb for warmth.
Infant rats can’t go to the bathroom by themselves. They’re stimulated to go only when rubbed around the genitals and anus. This is so the mother can ingest the waste and keep the nest clean. You need to stimulate the baby to pee every time you feed him. He may not poop every time, but he should poop at least every third feeding. Use a piece of toilet paper or tissue and gently flick it across the genital area for at least 30 seconds after every meal to take care of this important hygiene matter. If you fail to do so, the rat will die of toxic poisoning from his own wastes. Baby poop is normally soft and yellow or brown until they start eating solid food.
You can clean the baby of spilled food after meals with a damp cotton ball or by dipping him in a warm bath up to his neck and rubbing away the food. Be sure to dry him well. Also give him a full massage after every meal just as his mother would lick him to stimulate his circulation and help him to grow.
It is not unusual for orphaned baby rats to lose their fur or develop peeling skin. Don’t worry about it. The skin will heal and the fur will eventually grow back, usually before wild rats are ready to be released. If by some chance it doesn’t, you must wait until it does grow in before releasing them.
If the baby starts making a clicking sound when breathing that means that he has developed pneumonia and will die without treatment with amoxicillin. Pneumonia can also cause the baby to become weak, cold, and inactive. Mix a 250 mg capsule in 7.5 ml of formula (stir well) and give the baby one tiny drop of the mixture 3 times on the first day (spread equally throughout the day and night) and then twice a day for the next 7-14 days, depending on how quickly the symptoms clear up. For more info on getting and using amoxicillin, see my article about Respiratory Disease.
If necessary, until you buy the correct formula, for the first day you can give the baby dilute sugar water, made with 1 cup hot water ¾ teaspoon sugar, and ¼ teaspoon of salt. Stir until the sugar and salt are completely dissolved. Discard this solution after 8 hours because it can quickly grow bacteria.
I recommend using human infant formula. The nutritional requirements for rats are closer to that of humans than dogs or cats, and if you look at the information on the components of rat milk at the bottom of the page, you’ll see that the percentage of protein and fat in the human formula most closely matches that of rat milk. Be sure to buy the powdered formula, and most rats prefer the soy formula, not the milk-based formula. All human formula contains iron, and all babies need iron, so don’t worry when it says “Now with iron” on the label. Note: The Esbilac Small Animal Goat’s Milk formula is formulated just like puppy Esbilac and is much higher in protein and fat, so I do not recommend it.
Here is the schedule for mixing the formula to give their system a chance to get used to the new formula slowly (this is especially critical for pinkies):
1st feeding 4 parts water to 1 part powder (eg. 2 teaspoons water to ½ teaspoon powder)
2nd feeding 3.5 parts water to 1 part powder (eg. 1¾ teaspoons water to ½ teaspoon powder)
3rd feeding 3 parts water to 1 part powder (eg. 1½ teaspoons to ½ teaspoon powder)
4th feeding 2.5 parts water to 1 part powder (eg. 1¼ teaspoons water to ½ teaspoon powder)
5th feeding 2 parts water to 1 part powder (eg. 1 teaspoon water to ½ teaspoon powder) Then use this mixture from now on unless the baby has problems. See below.
If a baby gets diarrhea, gets bloated or becomes dehydrated, go back to the mixture for the 2nd feeding and progress on from there. To test for dehydration, pinch the skin on the back and see how long it takes for it to go back down. If it takes more than a full second, the baby is dehydrated.
If the baby is still bloated after going back to the more dilute formula, then you can give the baby a homeopathic remedy called Nux vomica, which is good for digestive problems. You can get it at any health food store. Do not touch the pellets with your hands. Tip out one pellet into a ultra-clean dish and dissolve it in a bit of water. Then suck this up into a clean syringe and squirt it into the baby’s mouth.
To mix the formula, first warm the water to about 105°F (which will feel hot). It will cool as you mix in the powder and you want it to end up being about 100°F (slightly warm). You can measure out the amount of water in a tiny container and heat it in a microwave for a few seconds, or you can heat a quantity of water in the microwave or on the stove and then measure out the correct amount of water. Then mix in the powder. If you need to feed several babies, you need to set the container of formula in another bowl of warm water to keep the formula warm. A mug warmer (cheap at Wal-mart) is a great tool to keep the bowl of water warm while feeding.
The amount to give at each feeding is 5% the body weight (in grams) as cc (a ml is the same as a cc). So you multiply the baby’s weight in grams by 0.05. So if a baby weighs 6 g, it should eat 0.3 ml at each meal. (6 X 0.05 = 0.3) A baby who weighs 18 g should eat 0.9 cc. This is critical for pinkies, so you must have a gram scale to keep track of their weights. You can buy an electronic postal scale that will weigh in grams at a stationery store.
Newborn rats normally nurse about every 3 hours. You’ll need to feed pinkies every 3-4 hours during the day and once in the middle of the night for the first week and every 4-5 hours the second week. Feeding too often will prevent proper digestion.
However, getting the formula in baby rats can be a challenge. No matter what method you use, it can take 24-36 hours to get the baby used to nursing on the new nipple and the new taste of the formula, so don’t worry if it seems like the baby doesn’t want to eat at first. Just keep trying. Hold the baby upright, grasping it firmly at the neck. He or she will be very wiggly so you need to hold on pretty tightly.
They tend to grow very slowly until they are old enough to eat out of a dish and then they usually grow very quickly.
Unlike some other animals, such as baby squirrels, the risk of a baby rat aspirating (inhaling) formula is very very low, which makes them pretty easy to raise. However, it is very common for baby rats to suck the formula up their nose. If this happens you will know because it will actually come out the nostrils. Keep an eye on the nose and stop feeding if you see a whisp of white at the nostrils. Use a tissue to wipe as much formula from the nose as possible. The baby will try to sneeze it out. It will take the baby a little bit of time to clear the formula from the nasal cavities, so be patient and continue to wipe off any formula that appears in the nostrils. After a few minutes the baby should be ready to nurse again.
One of the best methods of feeding baby rats is to get an IV catheter or small rubber feeding tube from your vet. These will fit onto the tip of a 1 cc syringe which will help you carefully monitor the amount a baby eats. You will have to cut the feeding tube shorter but it will still be about 4 inches long. The end of the catheter or tube is about the same size as mother’s nipple, but you will still need to slowly squirt the formula into the baby’s mouth. You can also use an eye dropper with a narrow tip. Be careful not to overfill the baby’s mouth which can cause them to get the formula up their nose.
Below is the set-up I use. The catheter is longer than I’d like, but that’s how long it is before it tapers down. Notice how I’m holding the syringe. You will have much better control of it in this position rather than trying to push the plunger with your thumb. Also see that I have the small container of formula sitting on an electric mug warmer (set on high), which keeps it a perfect temperature for feeding. The formula cools down quickly after you suck it into the syringe, so you don’t want to suck up too much at a time. I do about 0.2 ml at a time. This baby is a 2-week-old Norway rat.
This 13-day-old roof rat baby is licking/sucking the catheter.
Another method is to use a tiny piece of rag and form a nipple from one corner. Start by dipping the “nipple” in the formula and squeezing drops into the baby’s mouth. Once the baby starts sucking on the rag, you can drip formula little by little onto the rag with a dropper so you don’t have to remove the nipple from the baby’s mouth. You can also use a clean eye make-up sponge, the little one on a stick.
You must have the rag, sponge or eye dropper in the baby’s mouth when it sucks so the baby sucks on the “nipple.” One person tried just dripping formula into the open mouths while the babies sucked, and the babies swallowed too much air. This can be fatal because rats cannot burp. Air bloating the stomach must be sucked out with a needle and syringe through the body and stomach wall.
Mixed formula can be refrigerated for 24 hours before you need to discard it. Warm only the amount of formula you need to feed. One way is to place it in a small container sitting in a cup of warm water. You can also microwave the formula if you are very very careful and only do it for 3-5 seconds at a time. Test the temperature of the formula on your wrist before feeding it. It should feel warm but not hot. When I’m feeding more than 1 or 2 babies at a time, I keep the formula warm on an electric mug warmer on high.
Once when I was hand raising a wild roof rat who was just under 2 weeks of age, I thought he hated the formula because he would lick a few drops and then open his mouth as if he was gagging. I finally realized he was opening his mouth to begin power sucking! Infants use their tongue and upper palate to create the suction. Once I got the eye dropper properly positioned up against the roof of his mouth he would suck down about 0.75-1 ml in about 5-10 seconds! All I had to do was lightly squeeze the eye dropper bulb.
This 13-day-old roof rat is power sucking!
Moving from the Nipple to a Dish
When the baby is a week old he will start to get hair. At two weeks of age his eyes will open and he will start to grow teeth. When his eyes have been open for 3 days he will be able to start eating formula out of a little dish. The best thing to use for a dish at first is a tiny lid from a bottle of molasses or mustard. You must place this on a flat magnet (upside-down) to keep the baby from tipping over the lid. The first time you put formula in the dish, do it just after feeding the baby so he can investigate it when he’s not really hungry. Otherwise, he will literally dive into the dish and get the formula up his nose. It will still take him a little while to learn to lick from the dish and you will need to give him a bath after almost every meal. After a few days, if you are feeding a group of babies, you can switch from the catsup lid to a larger baby food jar lid. Once he seems to know how to eat out of the dish, offer fresh formula in the dish at least 3-4 times a day. At this point, the baby should be able to urinate and defecate on his own, but it doesn’t hurt to continue to stimulate elimination before putting down fresh formula.
Once the baby is eating well out of the lid, you can stop the night and bottle feedings. You can also start offering foods such as rat blocks, dry oatmeal and other grains, and little pieces of fruit and veggies. (Soft food can be very messy for babies, and they can eat solid food fine at this point.) From the age of 2 weeks the baby will gradually start pooping and then peeing on his own. Depending on the individual, you can stop stimulating him to go to the bathroom when he is 2 ½-3 weeks old.
Until their fur becomes fluffy (at about 3 weeks of age), baby rats can’t keep themselves warm and you must continue to give them supplemental heat. By 3 weeks of age the rat will be eating mostly solid food, although he wouldn’t be weaned yet, so you should still be offering some formula. At this age you need to move the baby from a box into an escape-proof cage with a water bottle. When a domestic rat baby is about 3-4 weeks old, it is a good idea to get him or her another rat companion of about the same age. Rats are very social and need to learn how to get along with other rats as a baby. At 4 weeks you can completely wean your baby and stop giving formula, and congratulate yourself on a job well done!
Special Notes for Orphaned Wild Rats
The risk of disease when raising an orphaned baby rat is low. Most diseases that can be transferred to humans would quickly kill a baby rat. However, I recommend you use good hygiene and be sure to thoroughly wash your hands after handling the baby.
For an orphaned wild rat, the best thing is to release it when it is old enough. This is especially true if you raise more than one together as they will be more bonded to each other and less tame. If you really, really want to keep a wild rat or mouse as a pet it will take a lot of extra work. The most common wild rat in California and the southern states is the roof rat which doesn’t make a good pet. Roof rats are very hyper and agile and even when tame tend to be very nervous and flighty. In the other states, the most common wild rat is the Norway rat, the ancestor of the domestic rat and they can make pretty good pets if they are handled and socialized enough, but you must always remember they are wild and might bite if frightened.
If you decide you want to keep a wild rat as a pet, then you need to handle it as much as possible. This is especially true if you hand raise a litter of wild rats. Because they have each other to bond to, they will not bond to you unless you spend a great deal of time handling them. In the case of more than one orphaned wild rat, it is best to plan to release them.
If you decide to keep a wild rat as a pet, it is a good idea to raise it with another rat as a companion. Introduce the baby wild rat to a 4-week-old domestic rat when the wild rat is about 3-4 weeks old. By the time a wild rat is about 6 weeks old, it will probably be too late for it to accept a domestic rat as a companion.
You can release wild rats when they are 6 weeks old. You do not need to separate males from females, even if you must keep them longer. Wild rats do not reach sexual maturity as young as domestic rats, in fact, probably not until 12 weeks. The best place to release a roof rat is an area near a permanent water source, such as a creek, pond, lake, or river, where there are a lot of trees. This is also a good place to release a wild Norway rat, but a Norway rat does not need trees, just a source of water, a place to hide, and a source of food. Some water sources will also be a source of food, supplying fish, frogs, snails, etc. When the babies are 4-6 weeks old, you need to get them used to eating foods they will find in the wild. Offer them live mealworms from a pet shop (in a jar lid to keep them from crawling away), nuts in the shell, and a variety of different fruits, veggies, and grains.
Here is how to release a wild rat. When the baby is about 3 weeks old, give him a little box about 6″ square in his cage for a nest box. Cut a small rat-sized door in it for him. This box should be small enough to easily fit through the door of the cage. This will be the rat’s safe place. You will notice that he will get more and more wild as he gets older and is no longer a little baby and when you approach the cage he will likely run and hide in his box. You can give him shredded paper and dried grass to build a nest in the box. When it’s time to release the rat, reach in the cage and remove the box, using your hand to block the exit. Have packing tape ready and put a piece over the opening to seal it. Also tape closed the lid of the box, and you may also need to tape over any other entrances the rat has chewed in the box. Place the nest box inside another closed box, just in case the rat gets out of the nest box. Drive to the release location and place the nest box in place hidden by bushes, under a fallen tree, etc. Slowly peel off the tape. Leave some rat blocks or seeds next to the box for a temporary food source while the rat learns his new environment.
The time of day for the release is not critical. Although rats are mostly nocturnal, there are more predators out at night too, so during the day is probably the safest time to release a wild rat.
This is the cage I raise wild rats in. It measures 14" X 20" X 24" tall. It’s not a good cage for domestic rats, because the upper floor is made of ½" X 1" mesh, which pets rats can catch their feet in. However, wild baby rats have much smaller feet. (It’s also too small for domestic rats to actually live in.) There is also a wire mesh bottom, which I cover with rabbit food as litter. This wire bottom makes the cage almost escape-proof. As you can see, I have equipped it with an exercise wheel, wood sticks to climb on and a nest box. This is the box I will release the babies in when it’s time.
Rat Milk Components
Range Throughout Lactation (%)
Day Lactose Fat Protein
0 2 - 2.6 20 - 28.6 7 - 8.6
5 2.4 - 3 5.5 - 15 6.5 - 7.4
10 3 - 3.7 7 - 18 8 - 8.6
15 4 - 4.5 9 - 19 8.3 - 10
20 3.5 - 4.7 8 - 14 8 - 10
Rat Milk Summary
Protein range: 6.5 to 10%
Fat range: 7 to 28.6%
Comparison with commercial formulas:
Human Soy Baby Formula—best match
Esbilac (for puppies)—too high in protein and fat
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