Why Is My Border Collie So Small? 3 Reasons

Border Collies have a “normal” range of height and weight as a medium-sized breed, but some dogs are much smaller than average. If you notice that your Border Collie is so small, you may wonder why. Does being small mean there is something wrong with the dog?

Your Border Collie may be small due to its genetic makeup. Border Collie puppies usually grow until 18 months old, and some can grow bigger or smaller than others. If your puppy is healthy but smaller than average, it’s worth checking if it has underlying health issues that need to be addressed.

Read on to learn more about the “typical” size for Border Collies, why your pup may be smaller than you expected, and how to determine whether there’s anything to worry about.

Reasons Your Border Collie May Be Small

Dogs come in a broader range of shapes and sizes than any other mammal. Even within breeds, the differences in size, color, and other physical characteristics can be remarkable. According to the American Kennel Club, Border Collies have 17 standard colors, and 4 acknowledged non-standard colors. 

The typical size range is a bit more limited but still leaves some room for variation. 

An adult male Border Collie typically stands between 19 and 22 inches (48.3–55.9 cm) high at the shoulder and weighs between 40 and 55 pounds (18.1–24.9 kg). Meanwhile, a female Border Collie is 18–21 inches (45.7–53.3 cm) tall and weighs 30–45 pounds (13.6–20.4 kg). 

However, those numbers are only typical ranges. Some male and female Border Collies fall well outside the so-called “normal” size for their breed. If your dog is on the petite side, you may wonder why, as well as worry if it means something is wrong. 

Here are 3 possible reasons for your dog’s small size:

1. Your Border Collie May Inherit Small Genes

Dogs inherit multiple physical traits from their parents, and size is top of the list. Small parents make small puppies. If you got your Border Collie from a reputable breeder, they should be able to tell you how big your dog will be at a certain age, based on the size of its parents.

Even experienced breeders, however, know that such a projection is an educated guess. There are countless stories of predictions gone awry when a dog winds up much larger or smaller than anticipated. 

The good news is that there’s nothing inherently problematic about having a smaller-than-average dog. Even if your pup was the runt of the litter, as long as it came from a quality breeder and passed their basic health checks before coming to live with you, it could be as healthy and happy as any other dog.

2. Your Dog Is Probably Still Growing

Most Border Collie puppies weigh between 7 and 14 oz (.19–.39 kg) at birth. They grow rapidly until they’re around 3 months old, at which time their growth levels off, staying at roughly a pound (.45 kg) a week until they reach six months.

Because their initial size varies from puppy to puppy, their weight at each stage will also vary. As long as they gain enough weight to stay on their growth curve, they are growing appropriately. Overall weight is less important than the percentage gain over time.

There is one important thing to note, however. Growth during this stage can be erratic, coming in spurts and stalls. Your pup’s appetite will likely be erratic during this period as well. There will be days when your dog needs to eat more than the recommended quantity of food. During these phases, it’s fine to feed your dog according to their appetite, not what’s on printed guidelines.

Border Collies generally reach their full height sometime between 12 and 15 months of age. Reaching full adult weight, however, usually takes a bit longer—up to 18 months. By this point, you’ll have a firmer idea of how big a dog you’re going to have. 

Even at their full height and weight, however, your dog may still act like a puppy. Female border collies are considered adults at 2 years. Males take even longer, not reaching adulthood until 36 months.

3. Your Dog May Have an Undiagnosed Health Problem

Small doesn’t mean unhealthy. There are plenty of smaller-than-average dogs in every breed in perfect health. In an adult dog, being smaller than the breed standard does not predict health problems. 

In fact, smaller dogs have several advantages over larger dogs. They may experience fewer joint problems and have less tendency to put on excess weight.

In puppies, however, persistently slow or absent growth can be a sign of something wrong. 

The most common cause of stunted growth in puppies is infection by intestinal worms. There are many kinds of parasites your pup can pick up that can, if untreated, become significant enough to siphon off the nutrition your dog needs to grow. 

Fortunately, worms are easily treated by medication. If you suspect your dog has worms, call your vet. You can have your dock back on track within days.

A more serious, though thankfully much rarer, the concern is a liver abnormality called a portosystemic shunt. It’s a congenital abnormality usually detected in young dogs, though some dogs don’t show symptoms until later in life. 

Depending on the severity of the problem, it can be managed with medication or corrected through surgery. In severe cases, however, euthanasia is a common outcome.

Final Thoughts

If your adult Border Collie is smaller than average, there’s no need to worry, especially if there are no other signs of health problems. In puppies, size can correlate to health, but that doesn’t necessarily mean they are unhealthy. Some Border Collies are smaller than average due to their genetic makeup.

If your dog is eating, growing, and behaving normally, your dog may likely remain petite in its lifetime. It will help to contact your dog’s breeder for information regarding the dog’s history, to be sure. You may also seek advice from your local vet.


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