I have methanol extract of feeds which contains Oxytetracycline and fatty acids and carotenoids. The color of the extract is brownish yellow. By using SPE how can I remove those fatty acids and carotenoids.

You can use a reversed-phase SPE sorbent (such as Oasis HLB) and then extract oxytetracycline with a mixture of water/methanol, while the fatty acids and the carotenoids stay behind. You need to experiment a bit, how much methanol you need to extract the oxytetracycline completely, while leaving the other stuff behind.