Known as a medium-sized breed, the border collie weighs between 30 and 45 pounds full-grown. As they're born weighing less than a pound, border collies undergo a near-miraculous transformation of height and weight. Growth-rate is dramatic during the newborn and puppyhood stages and plateaus around late adolescence.
Newborn
Newborn border collies are tiny, compact packages of organs, skin and bones. With a birthweight of 7 to 14 ounces, border collies are smack in the middle of the birthweight range for medium-sized breeds. Every puppy gains weight at a different rate, but each puppy should gain weight steadily. While a puppy may lose water weight the first 24 hours, a healthy puppy immediately begins putting on weight after that point. Within the first week, border collie puppies double their birthweight and for every week after that until 6 weeks of age, they gain 1/2 to 1 1/2 ounces a day.
Puppy
At 6 weeks of age, your 3- to 6-pound border collie has more than quadrupled his birthweight already. During puppyhood, your highly active critter will gain about 2 to 4 pounds a week until roughly 14 weeks of age. Around that point, the extremely rapid weight gain levels off and your pooch will gain about a pound a week until he's 6 months old. Remember, though, that every puppy is an individual and gains weight at a slightly different rate.
Adolescence
When entering adolescence, most border collies have achieved their adult height of 18 to 22 inches tall at the shoulder and they weigh 21 to 35 pounds. This border collie stage is known for gangly, tall, rangy pups that haven't quite filled out yet. Most teenaged borders eat ravenously to support their extremely high energy levels and metabolism. While your border collie will continue to gain weight throughout adolescence, it'll be a far slower, gradual process than it was in puppyhood. Expect a struggle to keep weight on a juvenile border collie; they're notorious for being hyper-metabolic. Keep your growing pooch on a high-quality, calorie-dense food to support his never-ending activity and movement.
Adult
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Possessing a thick, glossy coat, intelligent, intuitive eyes and an athletic, lithe body, the adult border collie that has finally moved passed the awkward teenaged stage and gained enough weight to fill out is truly a sight to behold. Adult borders weigh 30 to 45 pounds at maturity and typically don't struggle to maintain a healthy weight. While senior borders may need to be watched for weights that slowly creeps upward, adult border collies are active enough to keep a paunch at bay.
References
Writer Bio
Since 2001, Kea Grace has published in "Dog Fancy," "Clean Run," "Front and Finish" and an international Czechoslovakian agility enthusiast magazine. Grace is the head trainer for Gimme Grace Dog Training and holds her CPDT-KA and CTDI certifications. She is a member of the APDT and is a recognized CLASS instructor. She's seeking German certification from the Goethe Institut.