How to Fatten up a Runt Puppy (The Safest Way)!

As a mastiff breeder, one thing that I am often asked about is weight. While I always say that a dog will end up where he is meant to be, that even the runt puppy could end up as the largest dog, weight is something that we often worry about. This is especially true when that little runt puppy doesn’t seem to be gaining as quickly as the other pups in the litter.


In my chosen breed, the runts can be considerably smaller than other dogs but it can be stressful whether your puppies are the largest breed or the smallest. While I stress never to overfeed your runt puppy, there are things that you can do to help fatten him up so he stays healthy and grows on the proper arch for his size.


What is a Runt Puppy?

Runt puppies are smaller pups.

When you ask most people what a runt puppy is, they often think of size alone. A runt puppy is the smallest puppy. While that is the truth, it is not the only characteristic that you will see in your runt puppy.


A runt puppy is one who is small in size but also tends to be one of the puppies that is struggling. This can often be seen in not being able to fully suckle on a nipple or him having a weak suckle. Because of this, a runt is often pushed off the nipple by stronger siblings.


Another characteristic is that you may see more health problems with the puppy, it can be because he’s not getting enough food or because he didn’t get enough colostrum from his mom in those first few days of life. It can also be that he has something physically wrong with him.


In general, runt puppies are not only smaller but tend to have weaker frames and are fragile in appearance and when you hold them.


Although it doesn’t always happen, some mothers will ignore or push away the runt if there is something wrong with it. It is important that as a breeder, you monitor the litter and make sure that the puppy gets some one on one time with mom and a good nipple.


Risks for Runt Puppies

A runt puppy will seem more fragile than his siblings and is at greater risk of complications.

Runt puppies come with their own challenges and it really is important to stay on top of their care. Some of the risks that can be associated with runts are:

  • Weakened Immune System: This ties in directly with the colostrum from mom but if your runt puppy doesn’t get enough colostrum, he could have a weaker immune system, that will put him at greater risk for various viruses and bacteria that he is exposed to.
  • Parasites: All puppies are prone to parasites, which is why we deworm frequently through those first 8 weeks. Parasites, such as worms, can lead to poor weight gain and growth. For most puppies, it can be corrected, for runts, it can be devastating and even deadly. Runts do not have the strength to fight off the effects of parasites until the first deworming so it is important to discuss options with your vet.
  • Fading Puppy Syndrome: This is when the puppy fails to thrive and can be caused by a number of factors. Runt puppies are more susceptable to fading puppy syndrome.
  • Hypo and Hyperthermia: Finally, puppies cannot regulate their body temperatures. Runt puppies have a harder time coping with temperatures and can succumb to either hypothermia (too cold) and hyperthermia (to warm) quickly.


Being aware of the risks will help you treat them quickly and effectively so that you can save your runt’s life.


Myths about Runt Puppies

Before we move on to how to fatten up your runt puppy, I want to take the time to go over a few myths about runt puppies.

Myth #1 : Every Litter Has a Runt

Some litters have runts and some don't.


This is a complete myth. While you can have smaller puppies in the litter, you can have litters without a true runt puppy. In fact, most of my litters have no runts at all. Puppies are only a few ounces different at birth and stay less than a pound difference between the smallest and largest as they grow.


Myth #2 : The Runt Will Always Be Small

Runt puppies have big dreams too.


If this was the case, there wouldn’t be so many surprised people who purchased the runt of the litter. With proper care, a runt has the potentional to be the largest adult dog in the litter. In fact, I had one runt in an all girl litter. At a year old, she went from 18lbs when she went home to a 145lbs; outdone by only one sister who was 160lbs at the same age.


Myth #3: The Runt is One that Was Conceived Last

Birth order does not determine which pup will be the runt.

As you know, a bitch ovulates over a period of 48 hours and the eggs mature 24 hours after release. What this means is that eggs are being released during that entire 48 hour period and can be fertilized at any time once it has matured and before it dies. So there can be fertilization over that period with puppies being slightly behind in development by a few days.


While this can mean that a puppy is smaller, it does not mean that it is the runt. The runt can be one of the first or one of the last conceived. Really, what is believed to create a runt is a puppy that has a very poor implantation site. This means that they aren’t getting as much nutrients as the rest of the puppies around him or her. Age of conception and placement in the uterus does not determine if a puppy is a runt.

Myth #4: It is Better to Let Nature Take Its Course

Runt puppies can live full and healthy lives.

At one time, breeders may not give any attention to the runt, following a “only the strong survive” mentality, but that is not the case any longer. Runts, even if they have some health problems at birth, can grow up to live long, healthy lives free from health problems.


There is so much that you can do to help a runt thrive and to also fatten him up that there is no reason to just let him fight to survive on his own.

Practical Tips On How To Fatten Up A Runt Puppy

Now that we’ve looked at some of the myths around runts and what a runt puppy is, let’s move on to tips.


Tip #1 : Have a Scale

Get a good quality scale to weigh all your puppies.

I am a fanatic about weighing my puppies for one simple reason, if there is a problem, it often shows in the weight. A puppy that isn’t gaining or is losing weight, is in distress and needs intervention. In fact, you should expect to see a daily weight gain of 5 to 10% of their birth rate. I also look for their weight to double by a week of age, or shortly after.


My rule of thumb is to weigh all your puppies including your runt when they are born. Then weigh them once or twice a day for the first week. I do twice a day for the first week and sometimes more. Be sure to document the weights.


With the runt puppy, take the time to weigh him several times a day. In addition, if I am not sure how well a puppy is nursing, I will weigh him immediately before and after eating. While it won’t be a huge weight gain, you should see some with a full tummy. If there is no difference, then he is not getting anything and you’ll know to top him up.


Tip#2 : Test the Suckle Reflex

Full puppies will be quiet and content.

One thing that is often seen in runt puppies is that they lack a strong suckle. This means that your puppy can’t get anything from the nipple or he has to put too much effort into suckling for such little outlet that he tires before he can get a full meal.


When you have a runt, I always recommend that you place your finger in his mouth and see how strong his suckle is. If he doesn’t have a strong suckle, then you need to offer him milk through tubefeeding or another means.


If he is newborn, I recommend expressing some colostrum from the mom so you know he is getting the important nutrient. You can also use plasma for nursing puppies so they will have access to that important immune system from mom. Speak to your vet about this option. The usual dose for plasma is 5cc per puppy 3 times daily for the first 24 to 48 hours.


Tip #3 : Check for Physical Conditions

There can be physical reasons why you have a runt puppy.
A puppy with a cleft (A) and without (B)


There can be a number of reasons why the runt is small or is not gaining weight. These can be things such as a cleft palate or a cardiovascular issue. If you can’t see anything physically wrong with the puppy, I recommend that you take him to the vet to be positive as soon as possible. Some things can be treated, but some things the breeder will need to make the difficult decision on whether to let him go or not.


Tip #4: Keep him Warm

Incubators are an excellent way to keep your runt puppy warm.

As mentioned, runt puppies are susceptible to hypo and hyperthermia. This means that they can get cold or hot very quickly. Make sure that the runt is in a separate bin on his own and has a steady temperature of between 95 to 100 degrees Fahrenheit. While you can keep him with his siblings, if he is frail and a lot smaller, it is better to separate him until you are sure he is gaining and on the path to good health.


While you have him separated in his own incubator set up, monitor his internal temperature with a rectal thermometer. Puppy temps should be:


  • Newborn to 7 days old: 85º to 90ºF
  • 8 to 14 days old: 80º to 85ºF
  • 15 to 21 days old: 75º to 80ºF
  • 22 to 28 days old: 70º to 75ºF

I also find that direct skin to puppy contact is good for maintaining body heat but he will need a warm bin.


Warm puppies do better at digesting their food and nurse better as well so there are added benefits with keeping him warm.


Tip #5: Place him on the Back Teats

Put the runt puppy on the back nipples for the most milk.

If your runt puppy is suckling, I would encourage him to nurse from mom on his own. When I do, I place him on the back nipples, which usually produce the most milk. He may need you to hold him so he can stay on but he might be able to do it on his own.


Remember to weigh him. If he is making a lot of noise after eating, that means he didn’t get enough. If he’s quiet and content, weigh to confirm but he should be full.


Tip #6 : Top him Up

Tube feeding is an invaluable skill to learn.

With a puppy who is not suckling, or one who isn’t getting enough, even when he suckles, the option is to top him up or feed him his entire meal. With a puppy not suckling, you will need to tube feed him. For one that is, you can bottlefeed your runt puppy.


If you can, use mom’s milk, however, if that is not an option, purchase a puppy milk replacer or use a recipe for it. My favorite recipe is from Leerburg; however, mine is altered slightly and has proven to be the best for my puppies. It contains:


  • 1 1/4 cup of goat’s milk
  • 1 cup of high fat plain yogurt (I use 6% and above, making sure there is no xylitol in it)
  • 2 raw egg yolks (do not use the egg white as it can make puppies sick. Leerburg puppy formula calls for 1.)
  • 1/2 tablespoon of Karo Syrup or white corn syrup (must be white. Leerburg calls for 1/2 teaspoon)
  • 1 tablespoon of Mayonnaise (whole fat, and always check for xylitol)


This formula can last for 7 days in the fridge but I often make it daily and sometimes several times a day if I have to bottlefeed a number of puppies.


It helps pups gain very quickly. However, be sure not to overfeed. Puppies should be fed about a half ounce of puppy formula for every ounce of puppy weight per day. So a 10 ounce puppy should receive 5 ounces of puppy formula spread out over feedings every 2 to 3 hours.


Tip #7 : Remember to Potty

Use a damp cloth or swab to stimulate your runt puppy to poop.

Finally, remember to potty your runt puppy to make sure he is having regular bowel movements. If mom is pottying, that is great, just watch to make sure he goes to the bathroom. If she isn’t, take a warm cloth and gently stimulate his bottom until he poops and pees.


It should be noted that formula fed puppies can have firmer stools so be aware of that when you are pottying him.


Runts can be fattened up but it takes a lot of time and dedication on the breeder’s part. You will have to feed him on his own, top him up and constantly watch his weight as he grows and this will continue until he is eating on his own in a healthy manner.


But seeing a runt bounce back and become the amazing dog you knew he would be is worth the effort. As anyone who breeds knows, it’s the runts that often capture our hearts as breeders.