The Border Collie diet should include animal proteins, healthy carbs, vitamins, minerals, and omega fatty acids--nutrients every dog needs to maintain its health in the long term. This means the best dog food for Border Collies is premium dry kibble, as it has balanced portions of the above-listed ingredients. If consistently fed a premium brand like Royal Canin, Border Collie dogs will be much healthier and longer-living.
And how much should a Border Collie eat? Border Collie dog food portions for adults, depending on their age, size, and activity level, is about 2½ cups of dry food per day, divided into two meals. Border Collie puppy food portions are a bit less: again depending on age, about 1¾ cups per day, divided into three meals (not two) until six months of age.
For more info on how much to feed a Border Collie from puppyhood through maturity, see this Border Collie feeding guide:
Dog AgeDog WeightFood TypeAmountFrequency2 Months7 lbsDry (Puppy formula)0.25 cups3x/day3 Months12 lbsDry0.33 cups3x/day6 Months25 lbsDry0.6 cups3x/day9 Months33 lbsDry* (Puppy/Adult)1 cup2x/day12 Months+40 lbsDry (Adult formula)1.25 cups2x/day*--Around this time, transition to adult food by mixing in adult formula with the puppy formula, in slowly increasing amounts with each meal, for one week.
Try if possible to stick to the above-listed portions. Though not especially prone to obesity, if these dogs are constantly overfed (and under-exercised) they certainly can become overweight--and fat Border Collies will have numerous health problems and potentially shortened lifespans. You can help control your BC's weight by having consistent feeding and exercise schedules, by not feeding the dog table scraps, and by not leaving food in the dog's bowl all the time.
If you're worried your Border Collie is overweight, try this simple test: run a hand along the dog's side, and if you can't feel any ribs, it's diet time--which means less food and more exercise!