Why Is My Puppy Not Growing? Causes and Next Steps

By Dr Duncan Houston

A puppy that stays smaller than its littermates can worry any owner. Some size differences are normal, but a flat weight trend, weight loss or poor condition deserves a closer look.

The goal is healthy development for that puppy, not catching up with the largest dog in a photograph.

Quick Answer

Poor growth can result from inadequate intake, an unsuitable diet, parasites, digestive disease or congenital and hormonal problems. Normal growth also slows as a puppy approaches maturity, with timing varying by expected adult size. Arrange a veterinary assessment for unexpected plateauing, weight loss or other symptoms, and do not add calcium or growth supplements without a diagnosis.

Confirm what has changed

Use the same reliable scale under similar conditions and record dates and weights. Bring earlier veterinary or breeder records if available. A single measurement, especially from different scales, may be misleading; the trend is more informative.

Weight is only part of the picture. Your vet will consider muscle, body fat, height, appetite, activity and expected adult size. Mixed-breed puppies may not match a single breed chart. You cannot tell that growth plates have closed by feeling the legs at home; imaging is used when there is a clinical reason to assess the skeleton.

Check the feeding details first

Write down the exact food, measured amount, treats, supplements and what the puppy actually eats. Another pet may take part of a shared meal, or a measuring cup may deliver a different amount than expected. Difficulty chewing, swallowing or retaining food can also reduce intake.

A puppy needs a complete diet suitable for growth, including large-breed growth when applicable. AAFCO’s label guidance explains nutritional adequacy statements. Adult maintenance food, meat alone or an improvised homemade recipe may not meet growth needs.

Do not try to accelerate growth with extra calories, calcium, bone meal or vitamin mixtures. Overfeeding can produce excess body fat, and mineral imbalance can harm development. A nutrition plan should support steady growth and appropriate body condition.

Parasites and digestive problems

Intestinal worms can contribute to poor condition, diarrhoea and anaemia, particularly in young puppies. Cornell’s hookworm guidance highlights the greater risk of clinical illness in puppies. Parasites are one possibility, not a diagnosis established by a pot belly or small size.

Your vet may recommend faecal testing and an appropriate treatment programme. Report every previous dewormer, dose date and the puppy’s weight at treatment. One treatment does not rule out all parasites, and persistent signs may require reassessment rather than repeatedly giving the same product.

Chronic diarrhoea, vomiting, regurgitation or poor nutrient absorption can also affect growth. The pattern helps guide investigation. A puppy eating eagerly but losing condition needs assessment rather than simply a larger food bowl.

Congenital and hormonal causes

Some puppies are born with conditions that affect nutrient use or overall health. A portosystemic shunt allows blood to bypass normal liver processing. The American College of Veterinary Surgeons describes possible digestive, neurological and urinary signs, which may occur alongside poor development.

Rare hormonal disorders can also cause abnormal growth. The Merck Veterinary Manual describes pituitary dwarfism as an inherited disorder that may affect growth and coat development. A small puppy alone does not establish this diagnosis, and hormone treatment requires careful veterinary supervision.

Heart defects, ongoing infection and other systemic illnesses may reduce a puppy’s ability to thrive. A painful or injured growth plate can affect an individual limb; this differs from general failure to gain weight. Report limping, limb angulation or reluctance to move.

What the assessment may involve

The vet will review the growth and diet history, examine the puppy and select tests according to the findings. These may include faecal, blood and urine tests, liver-function assessment, imaging or specialist referral. Not every small puppy needs every test.

Bring food packaging, medication records and photographs showing changes over time. After treatment begins, agree a weight-check schedule and the signs that require earlier review. Catch-up growth and long-term size depend on the cause; a rapid recovery cannot be promised.

When to seek emergency care

Collapse, severe weakness, tremors, seizures, breathing difficulty, pale gums, repeated vomiting or bloody diarrhoea needs urgent assessment. Very young or tiny puppies can deteriorate quickly when they stop eating. A cold, poorly feeding newborn is an emergency and needs a different care approach from an otherwise bright weaned puppy.

Frequently Asked Questions

Is the smallest puppy always unhealthy?

No. Individual variation exists, but growth trend and clinical condition should be checked.

Will deworming solve the problem?

Only if relevant parasites are contributing, and treatment must match the problem. Other causes may coexist.

Should I add calcium?

Not to a complete growth diet unless your vet identifies a specific need.

When should growth stop?

Timing varies with size, genetics and the aspect of development being measured. Your vet can interpret the trend for your puppy.

Measure progress, review what your puppy actually eats and investigate unexpected changes early. Healthy growth is a pattern to support, not a race to a target weight.

ASK A VET™ can help you organise feeding and growth records before an in-person veterinary assessment.