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If you are hoping for a small or medium size of dog and end up with one of Mongo proportions, that miscalculation may be significant. Alternatively, if you want a huge dog and wind up with a powder puff pooch you may be unhappy for that reason.
It is really important to know what you are getting into when you get a pup, in terms of its eventual size, exercise and grooming requirements, likely temperament, personality, and energy level – to name but a few important considerations. And size does matter! Big dogs need more space at home and in the car, may need special fencing, cost more to feed and medicate, and require more physical strength to control.
Estimating a pup’s eventual size is not too tricky when the dog is purebred. You may get a pretty good idea by looking at the puppy’s parent or by looking up breed standards in a book such as the American Kennel Club’s Complete Dog Book. Breed standards will tell you a typical weight range for each breed as well as height at the shoulder, length of the muzzle, and much more! Sure, there are the occasional runts but these can be picked out by eyeballing the litter and assessing if they’re all about the same size.
It’s mixed breed pups that are harder to assess when it comes to growth potential. This is especially true in a situation where neither information about the breed or size of the puppy’s parents nor the exact age of the puppy is known. This is not an uncommon situation in humane societies or shelters where puppies just show up.
The younger the pup is, the harder it is to predict what size it will eventually be. Some estimate can be made if the puppy’s age is known or if there is known information about the parents. Of course, the mom will sometimes be around to see, but it may be impossible to know information about the sire.
Here are some considerations to give you a handle on a puppy’s growth potential:
- Breed and size of both parents: Two 20-pound terriers will not spawn pups that will eventually stand 27″ at the shoulder and weigh 99 pounds. Likewise, 2 retriever-sized dogs will not give birth to pups that achieve a maximum weight of only 20 pounds. It just doesn’t happen. Difficulties arise in assessment of future size potential when one parent is big and the other small, though in such cases, the bitch’s size counts for more than the sire’s.
- Paw size: As with people, big feet indicate greater height (and therefore weight) potential. You can’t have a 100-pound dog doing a pas de deux on ballerina-sized paws. Again, it just doesn’t happen. Neither can you have a little Munchkin of a dog parading around on paws the size of large pizzas. Nature doesn’t design this way.
- Loose skin: The looser a puppy’s skin the more room he has to grow into his “new suit” and the larger he is likely to become.
- Growth curve: A relatively undocumented but nevertheless valid method of assessing a pup’s eventual size is to plot its growth curve. The really rapid phase of growth occurs from birth to 6-months of age. Thereafter growth slows to an eventual halt at 8-14 months of age (say, 12 months on average) depending on parental breed contributions. Either height at the shoulder or weight can be plotted on a chart to be assessed at intervals. For a dog that is properly fed, weight gain should be fairly steady throughout the growth phase. For example, a dog slated to weigh ~ 100 pounds should gain around 2.5 pounds per week after about 4-weeks of age. A dog slated to weigh half this size will gain weight correspondingly slower. For a 4-6 pound adult, the following weight gain applies: 10 weeks, 1 lb. 9 oz. – 2 lb. 6 oz., 12 weeks, 1 lb. 14 oz. – 2 lb. 13 oz., 14 weeks, 2 lb. 2 oz. – 3 lb. 3 oz., 16 weeks, 2 lb. 7 oz. – 3 lb. 11 oz. And a growth curve really is a curve: It will reach a “knee” when about 65% of the dog’s eventual weight is reached and plateau after 95% of eventual body weight is achieved.
- The “double-it” formula: Some say that whatever the puppy weighs at 14 weeks double it to get the adult weight.
- Height increase versus weight gain: There comes a point of a pup’s life at which growth plates of the long bones becomes fused and bone length no longer increases. In humans, growth plate closure of long bones occurs between 17-21 years of age though muscle mass continues to increase until full physical maturity at around 25 years of age. An equivalent thing happens in dogs. Though growth plates close between 8 – 11 months of age, body weight continues to increase until full adult maturity is reached maybe months later in larger breeds. A simple estimation for predicting adult height is that a pup will be 75% of its adult height at around 6 months of age.
If all of the above factors are considered, it should be possible to make a reasonable assessment of a pup’s estimated size and weight at maturity. And at least there will be no BIG surprises though admittedly even the best estimations are far from 100 % accurate.