"One company, Optibrand Ltd., further tightens the process with retinal scans of cattle to confirm their identity. Optibrand's scans are performed with readers that have global-positioning chips to record the animal's location."
Okay...tin foil time...what a great way to test technology that can be used to track humans. You force/induce/manipulate farmers into participating with this "chipping" scanning system which allows researchers to optimize data and refine the process for use in humans. Research costs are low because the company doesn't have to maintain large herds of millions of cattle, the farmers fund the research/developments costs by simply caring for their live-stock. Plus you watch and catalogue side effects and redesign accordingly.
The GPS tracking is the final piece of the puzzle, optimize that and the technology becomes available for the tracking of all humans!