Presently, RFID based ID for animals are available in 3 forms:
                                            1. External Ear Tag
                                            2. Injectable Tag for subcutaneous applications
                                            3. Ruminal Bolus

Injectable RFID tags are injected to remain under the skin of the animal. Delivery is through a special syringe. The advantage is that they are less painful, also there is no outside identification mark for a malicious person to know where the tag is embedded in order to remove it or modify it. The RFID chip inside the tag is generally ‘Read-Only” so that data once recorded cannot be modified.
Injectable RFID tagging system is being used for cattle today. Your cattle can easily be injected by this kind of syringe which embeds an RFID tag under its skin. The tags have no side effects and have an estimated life of 25 years. The size of the cattle is not a consideration, since the tag itself is very small, about the size of a rice grain. Hence these tags can be injected into any cattle, big or small, a ship or a Cow. Since it is injected under the skin, there is no possibility of the tag getting dirty, damaged or lost.

How will it work?

A RFID tag is coupled to the ear lobe of the animal. This can be done once any time during the life of the animal. There is no other procedure required throughout its lifetime, other than scanning by a remote reader. The number of the RFID tag is unique and cannot be altered. There are about a trillion numbers available, so there is no risk of duplication.When an animal is to be scanned, it is either brought near a fixed RFID reader or scanner, or simply a portable wand/Handhold reader (having a small reader inside) is used to sweep in the space near the animal and the tag is read.
The reader is connected (by means of wired or wireless connections) to a remote database which correlates the unique RFID tag number on the animal with other data on the animal. These other data fields may contain information about

Date of birth
Last vaccination done
Any medical history
Owner details
Bank/Insurance details

Of course these fields can be many more than the four described above. The data can vary but the principle remains the same.