because most Labs will more than pig out when given free choice- mine did. A pure Yellow Lab's weight range is 60-70 lbs with females on the low end, and males on the high end. Haven't checked it but probably a Chocolate Lab may be slightly higher, and a Black Lab slightly lower. If your Lab is too heavy then taking the weight off is the best thing you can do to counter any arthritis.

Giving both dogs glucosamine is probably a good idea. Also you should start supplementing their diet with fish oil. Try 2000 mg twice a day. Fish oil has many desirable properties as a supplement.