You have mated your cow with an injection and it has been 282 days still it has not given birth to a calf what should you do?

If by "injection" you are referring to artificial insemination (which is not considered an injection when breeding cows), and it has been only 282 days since she conceived then you are being too impatient. The normal gestation length for a cow (on average) is 285 or 286 days long. Gestation, however, ranges depending on the cow's breed. She can give birth at any time between 275 days to 300 days of gestation. So I suggest you be patient and let Nature take its course. Your cow will let you know when it is time that the calf should arrive.