What Causes Weight Loss in Rabbits and How to Help

Sometimes it will sneak up on you. When you spend time with your bunny every day, it’s hard to notice the small changes in weight over time. One day you’ll look at your rabbit and notice they seem different, skinnier than they used to be. Is your rabbit underweight, and should you be worried?

Significant weight loss in rabbits is most often caused by dental problems or another underlying health condition. Other possibilities include anxiety, old age, or an improper diet. The only way to know the cause is to bring your rabbit to a veterinarian for diagnostic testing.

From there you will be able to treat the condition that is causing your rabbit to lose weight. It may require hand feeding your rabbit and administering medication, or it may require a lifestyle change for your rabbit. Whatever the cause, it’s important to take steps to help your rabbit as soon as possible because lack of eating can cause other serious conditions, such as GI Stasis.

If you are concerned that your rabbit is underweight, visit your rabbit’s veterinarian for a diagnosis and to help create a plan for healthy weight gain.

How to know a rabbit is underweight

Healthy adult rabbits are not all the same weight. Breed, age, and activity levels play a large role in determining the ideal weight of a rabbit. A 4lb Holland Lop rabbit can be just as healthy as a 15lb Flemish Giant. So, the overall weight is not a very good indication of an under or overweight rabbit. Instead, you’ll need to look for other signs in your rabbit’s appearance and body structure.

If your rabbit is severely underweight, you can probably tell just by looking. They may have a sunken abdomen and very prominent ribs and backbone. However, that is not always the most accurate way to determine if a rabbit’s body fat is at a healthy ratio. For example, the fur of long-haired rabbits, like angora rabbits, will hide any visible signs of malnourishment.

That’s why the best way to determine if your rabbit is underweight is by feeling for their ribs, spine, and hip bones. When you feel for your rabbit’s ribs, spine, and hips, you should be able to feel the bones under a thin layer of fat. In a healthy rabbit, these bones will feel rounded to the touch.

If your rabbit is underweight, the bones will start to feel sharp when you touch them. There is no longer a layer of fat protecting these bones, so you’ll start to feel how pointed they are, along with all the bumps and ridges.

Body Condition Score (BCS) chart

1: Emaciated	No fat, with a visible spine, pelvis, and ribs that feel sharp when touched. Likely there will be a loss of muscle mass and there may be concave areas around the rabbits behind.
2: Thin	A very thin fat layer. The spine, hips, and ribs of the rabbit are easily felt and are somewhat sharp when touched.
3: Ideal weight	There is a healthy layer of fat, but no bulging areas. The spine, hips, and ribs can be felt, but are rounded and not sharp when touched.
4: Overweight	There is a thick layer of fat making it difficult to feel the ribs, hips, and spine. There may be some extra folds of fat and the bottom will start to become rounded on the sides.
5: Obese	It is very difficult or impossible to feel the hips, spine, and ribs. There are many layers of visible fat, and the stomach sags. The rabbit will be rounded on the sides around their bottom and abdomen.

Symptoms of dangerous weight loss in rabbits

If a rabbit loses too much weight, they will exhibit other symptoms as well. If a rabbit is too far underweight, you may need to help them by adjusting their diet, lifestyle, or screening for any other underlying conditions. Signs that your rabbit has lost too much weight include:

• Sharp or prominent spine, ribs, and hip bones
• Concave abdomen
• Sunken areas around their butt
• A rough or scruffy coat
• Small and few poops
• Lack of energy
• Dropping food from their mouth
• A hunched posture

Causes of weight loss in rabbits

Most pet rabbits are at more of a risk for obesity than they are for being underweight. However, that does not mean it’s a less dangerous condition. In general, rabbits lose weight as a result of improper living conditions, an improper diet, or other undiagnosed conditions.

This list includes some of the most common causes of weight loss in rabbits. Since the root cause can be difficult to determine and there may even be multiple factors, I recommend getting the help of a trained professional and not trying to make significant changes to your rabbit’s diet without guidance.

1. Dental disease

Dental problems are some of the most common health conditions seen among pet rabbits. Since rabbit teeth don’t stop growing, dental problems can result in overgrown teeth that make it difficult or painful for rabbits to eat. When this happens, rabbits will (understandably) eat less, leading to a significant loss of weight.

There are genetic causes of dental problems, but for most rabbits, a diet that is high in hay (especially timothy hay) will prevent overgrown teeth. 

• Read more: how to care for your rabbit’s teeth

2. Old age

As they age, many rabbits will end up losing weight. Most of this is inevitable due to the loss of muscle mass rabbits experience in old age. As a result, elderly rabbits will be less active which will further atrophy the muscles and cause weight loss.

To counteract this, it will probably be necessary to adjust your rabbit’s diet when they are older to include more calories and protein. Talk to your vet about healthy ways to increase food intake for senior rabbits and ways you can encourage more exercise and activity.

3. An improper diet

Most of the time when pet rabbits are given an improper diet, it’s because they receive too many pellets and it causes weight gain. A diet that results in weight loss is much less common, but it is possible even for well-meaning rabbit caretakers.

An unexpected cause of weight loss in rabbits is a diet that is too high in fresh greens and vegetables while being too low in high-fiber dried hay. This can cause problems because fresh leafy greens are not as calorically dense as dried hay is because of the extra water content. The rabbit might end up getting full off of the greens before they’ve eaten enough calories to maintain their weight.

Of course, there is also the possibility the rabbit is simply not being fed enough. Making sure the rabbit has constant access to hay and ¼ – ½ cup of dry pellets every day is necessary for helping rabbits maintain their weight and energy levels.

4. A partner rabbit is hogging the food

If you have multiple rabbits living together, they might have a problem sharing their food. Sometimes one rabbit will actively bully the other rabbit. They might be aggressive about guarding their food and not letting the other rabbit near the bowl until after they are finished. This will cause the second rabbit to get fewer calories than they need to sustain a healthy weight.

Even if it’s not a case of bullying, one rabbit may eat significantly faster than the other one. In the end, this can cause one rabbit to eat more than they should and gain weight, while the other doesn’t get enough to eat and loses weight.

If you find yourself in this predicament, you should observe your rabbits to see what the problem is. Once you’ve confirmed that one rabbit is hogging the food, you might need to consider separating your rabbits during mealtimes by luring them into separate areas with a fence in between them.

5. Underlying conditions

A common cause of unexplained weight loss is some kind of hidden underlying health issues. When rabbits feel pain or get sick it will often affect their digestion. They will lose their appetite and eat a lot less food than they normally would. If the illness goes undiagnosed for some time, this will inevitably result in an unhealthy loss of weight.

A rabbit veterinarian will have to help you determine what could be causing your rabbit to feel sick since there are a number of possibilities. These include:

• Infection
• Kidney conditions
• Gastrointestinal discomfort
• Cardiovascular conditions
• Cancer
• Metabolic conditions

6. Parasites

While it is less common, rabbits can also contract parasites that can result in weight loss. One such organism is called coccidia. This parasite actually lives within the intestines of many rabbits but is not a problem for rabbits who are healthy. It can, however, infect the liver and cause illness and weight loss in young or otherwise unhealthy rabbits.

External parasites, such as fleas and mites can cause weight loss in a more roundabout way. By causing a rabbit discomfort they can decrease the rabbit’s appetite. The rabbit will eat less and lose weight as a result.

• Related reading: Learn more about fleas and ear mites in rabbits

7. Anxiety

Rabbits can get stressed out pretty easily. The problem is when rabbits are chronically stressed, they’ll become anxious and it will affect their appetite. Rabbits who are anxious will be too stressed to eat, which will result in an unhealthy loss of weight.

If this is the case, the best thing to do is help your rabbit feel safe in their home environment. Make sure they are separated from other house pets (like dogs and cats), and they are placed in a quiet area of the home, rather than a room surrounded by activity and noise.

Over time, you can work to help your rabbit become more confident so that they don’t feel as anxious in their day-to-day life.

• Read more: how to help your rabbit overcome anxiety

8. Not enough water

If rabbits don’t have enough water to drink, they will also reduce the amount that they eat. Most of the time this will be because there is not enough water available, not because the rabbit is choosing to drink less. 

For example, if they consistently empty their water bowl before the end of the day (or flip it while you are away at work) they might also eat less since they are feeling parched. Alternatively, your rabbit might have a water bottle with a sippy spout, but never learned how to use it properly, causing them to drink less than they should.

The best thing to do is ensure your rabbit has a large enough water trough to last the entire day and night. Usually, you would want to get a large dog-sized bowl, rather than a smaller one that is marketed toward rabbits.

If your rabbit is a bowl flipper, you can give your rabbit both a bowl and a water bottle. This will ensure that your rabbit always has water available even if they decided to throw a tantrum at some point during the day.

9. The rabbit’s living area is too warm

In general, rabbits do not like being hot. Ideally, they would live in temperatures in the 50ºs and 60ºs (ºF), since hotter temperatures can make them feel stressed out. Between the stress and exercising less due to the heat, rabbits will typically have a smaller appetite as well. If they are chronically kept in hot conditions, they might start to lose weight.

It’s recommended that you keep rabbits in temperatures of 75º or less, and never place them directly in the sun without access to any places where they can get shade.

10. Not enough exercise

While it might seem like a lack of exercise would cause rabbits to gain weight (and sometimes it does), it can just as easily cause a loss of weight over time. Rabbits who are chronically sedentary will lose a lot of muscle mass. Unless they are overeating, the atrophied muscles will lead to weight loss.

This may be due to conditions such as arthritis, which makes it painful for rabbits to move around, or depression. But it can also be the result of a living area that’s too small for the rabbit.

• Learn more about how much space pet rabbits need to stay healthy

What to expect during a heavy shedding season

It’s pretty common for rabbits to lose a little bit of weight when they are molting. During this time, the rabbit is regrowing an entire coat of fur which does temporarily require more protein for the production of the strands of hair. 

This is not a drastic loss of weight, but the growth of new fur might require the rabbit’s body to utilize proteins from their muscle mass, making them appear thinner overall. However, weight loss as a result of molting should not be drastic and it should be temporary. The rabbit’s appearance should return to normal within 1-2 weeks (but with a new coat of fur).

This slight loss of weight is usually unnoticeable going into the winter months because the new, fluffier coat of fur will cover up the weight loss. However, going into summer it might appear worse than it is. Since rabbits lose the fluffy coat and a small amount of muscle mass at the same time, it will seem like a sudden change. As long as your rabbit’s behavior is normal, there is little need to worry about weight loss during this time.

When to visit your veterinarian

If you notice your rabbit has lost significant weight, it’s recommended to check in with your veterinarian as soon as possible. This is especially true if the weight loss has persisted over several weeks, or if you’ve noticed any secondary signs of serious weight loss, including a lack of energy, dropping food, or smaller poops.

Sometimes, a rabbit is losing weight for different reasons that were mentioned in this article, or as a result of multiple health problems. To accurately understand the weight loss and treat your rabbit accordingly, it’s very important to take the step and seek out the advice of a veterinarian.

What kind of treatment to expect

The treatment for an underweight rabbit will vary depending on the cause of the weight loss. Some rabbits will only need a corrected diet or different living conditions, but others will require more medical intervention. Depending on the root cause, surgery may even be required.

In most cases, if your rabbit is underweight, you should expect to:

1. Syringe feed critical care. Critical care is a powdered food formula that you mix with water to make a mush that you can hand feed a rabbit. Learn more about critical care for rabbits.
2. Medication for pain management. Depending on the cause, you might also have to administer pain medication to help your rabbit’s appetite return to normal.
3. Reduce stress as much as possible. Help your rabbit stay comfortable in a quiet place without too many distractions.
4. Follow your veterinarian’s advice. Your rabbit’s vet will be able to give you specific care instructions for any underlying illness or change in diet.

The importance of annual wellness exams

Unless it is drastic, weight gain and weight loss can be difficult to detect in pet rabbits. Most of the time it will be a slow change over time that you won’t notice in your day-to-day life. That’s why it’s so important to have a regular veterinarian who can keep a record of your rabbit’s overall health.

Your rabbit vet will keep a record of their weight over time so that they can immediately detect if there has been any kind of unusual weight loss. Once detected, your vet will be able to run some tests and evaluations to figure out the cause of your rabbit’s weight loss and help you create a plan to encourage healthy weight gain.

Sources:

1. House Rabbit Society. “Practical Nutrition.” Youtube. Commentary by Susan Smith Ph.D. Nov. 7, 2014, https://www.youtube.com/watch?v=91mSv1PqyY4.
2. Laurie Hess, DVM; Rick Axelson, DVM. “Coccidia in Rabbits.” VCA Animal Hospitals. https://vcahospitals.com/know-your-pet/coccidia-in-rabbits
3. Marie Mead with Drs. Susan Brown, Tomáš Chlebeček, and Jason Hutcheson. “Overweight and Underweight Rabbits.” House Rabbit Society. January 30, 2013. https://rabbit.org/overweight-and-underweight-rabbits/