I wonder if it may be useful to be aware of the availability of audit reports on the Food Standards Agency's website. These are documents of the FSA regulating local authorities regarding their feed and food law enforcement activities.
In a nutshell .... part of the audit covers visiting a local feed business and samples being taken by an agricultural analyst which is in turn analysed by a laboratory.
With this in mind, I'd be inclined to approach a local authority and ask to speak to their appointed "Agricultural Analyst" who might be willing to offer further guidance to help with progress. [May also mention which laboratories are used and (one hopes
) at a reasonable cost].
Another idea to explore involves approaching other feed businesses in the local area as to whether it may be agreeable to send several (batches) together, as I'm wondering if laboratories may offer bulk testing at reduced rates.