Sometimes calves are born with contracted flexor tendons that result in the calf walking on the front of the toes. Most often this resolves with a week or so without any special care. Sometimes a cast is used to help stretch the tendon and, rarely, it is necessary to surgically correct the problem. Administration of high doses of tetracycline has been reported to help contracted tendons in horses and this is probably the basis of the recommendation given to you. However, there is no evidence that this treatment is effective in calves. Further, high doses of tetracycline cause kidney failure in young calves. A 15 cc dose of LA200 is the label dose for a 600 pound animal.
Finally, remember that it is unlawful to use an animal drug except as it is labeled unless the recommendation comes from a veterinarian. Veterinarians may prescribe medications in an extra-label fashion under certain circumstances.
Give the calf a few more days to stretch the tendons on its own. Have a veterinarian examine the calf and make recommendations on casting or surgery if this is unsuccessful.