What this means
Puppies in a litter are born different sizes, and some are simply slower out of the blocks. Size is not the only thing that matters; how the puppy behaves matters too: whether it is playful, eats eagerly and keeps up with its siblings. A small but bright, well-rounded puppy is less worrying than a small one that is dull or thin.
Many of the reasons a puppy grows slowly lie inside the body: malformations of the blood vessels of the heart or liver, underdeveloped kidneys, bone or metabolic disorders, and immune system problems. These are not things an owner can spot or put right at home. Sometimes a puppy just looks small, and the real cause only comes to light after blood tests or a look at the heart.
It helps to write things down: weigh-in dates and weights, how the puppy compares with its littermates, whether it eats, how it urinates and passes stools, whether it tires quickly, vomits or limps. If you can, compare with the other puppies in the litter. Your vet will also ask about vaccinations and worming, so bring your notes along.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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A blood vessel problem of the heart from birth
A vessel that should have closed after birth can burden the heart and lungs. A puppy may tire sooner, breathe faster and grow more slowly.
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A blood vessel that bypasses the liver
When some blood bypasses the liver it cannot clean the body properly. A puppy may grow poorly and behave oddly, especially after eating.
About the condition: Liver shunt (portosystemic shunt) -
Underdeveloped kidneys
If the kidneys did not develop fully, a puppy may drink and urinate more, be thin and be smaller than its littermates.
About the condition: Renal dysplasia -
A disorder of bone metabolism
When bones do not mineralise properly a puppy may grow poorly and the bones may be weaker or painful.
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An inherited storage disease
Some inherited disorders cause substances to build up inside cells. A puppy may grow more slowly and show signs from the nervous system.
About the condition: Storage disease (lysosomal storage disease) -
An inherited immune system disorder
Puppies of some breeds are born with an immune system problem that leaves them often ill and growing poorly.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- The puppy's weight and weigh-in dates compared with its littermates
- Whether it eats eagerly or turns food down
- Whether it tires sooner or plays less than the others
- Whether it breathes fast or coughs
- Whether it drinks and urinates more than usual
- Whether it vomits, has diarrhoea or often falls ill
When to book a routine visit
If a puppy falls clearly behind the others, gains very little or seems duller, book a visit rather than waiting for it to catch up. Bring your weight notes and describe how the puppy behaves.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Hypophosphatasia Bones and joints Hypophosphatasia is an inherited metabolic disease in which the body lacks enough of an enzyme that helps bones and teeth mineralise properly. As a result, bones stay softer and more fragile, and teeth may be poorly anchored. Its signs can show while the puppy is still growing, and it can seriously affect growth and mobility.
- Patent ductus arteriosus (PDA) Heart Before birth, blood bypasses the lungs through a small vessel called the ductus arteriosus, which should close shortly after birth. If it stays open, some of the blood flows where it shouldn't, so the heart has to work harder and is gradually worn down. It is a congenital heart defect that a vet may hear as a distinctive heart murmur when examining a puppy.
- Renal dysplasia Kidneys and bladder Renal dysplasia is an inborn disorder in which the kidney tissue forms abnormally as the puppy grows and stays immature. Such kidneys filter the blood less well, so waste products build up in the body and a young dog can develop kidney failure. The disorder ranges from mild to severe, so how much it has affected the kidneys is for a vet to assess.
- Storage disease (lysosomal storage disease) Hormones and metabolism This is a group of inherited diseases in which cells lack an enzyme needed to break down certain substances, so these build up inside the cells and gradually damage them. Depending on which substance builds up and in which organs, the signs vary widely: the disease can affect the brain, nerves, eyes, liver or bones. Because there are many forms, which one is affecting a dog is for a vet to establish.
- Trapped neutrophil syndrome Blood and immunity This is an inherited immune disorder in which the bone marrow produces neutrophils, the white blood cells that fight infection, but they cannot get out into the bloodstream. As a result the puppy is left nearly defenceless against bacteria, and infections keep coming one after another. A genetic test exists for the disease, so breeders can screen their breeding dogs.
- Liver shunt (portosystemic shunt) Digestion and liver A liver shunt is an abnormal blood vessel that carries blood from the intestines around the liver instead of through it. As a result, the liver cannot clear the toxic substances coming from the gut, and they enter the general circulation, affecting the brain and the whole body. A shunt can be present from birth or develop later because of other liver disease.
Body systems: Bones and joints Heart Kidneys and bladder Hormones and metabolism Blood and immunity Digestion and liver